Title: Substituted cyclodextrin as a model for a squid enzyme that hydrolyzes the nerve gas soman Hoskin FC, Steeves DM, Walker JE Ref: Biological Bulletin, 197:284, 1999 : PubMed
Title: Organophosphorus acid anhydrolase in slime mold, duckweed and mung bean: a continuing search for a physiological role and a natural substrate Hoskin FC, Walker JE, Mello CM Ref: Chemico-Biological Interactions, 119-120:399, 1999 : PubMed
Recently, and for the first time, a diisopropylphosphorofluoridate (DFP)-hydrolyzing enzyme, i.e. an organophosphorus acid anhydrolase (OPAA), has been reported in a plant-source. Based on this and other suggestive evidence, the ability of three plant sources and a protist to hydrolyze DFP and 1,2,2-trimethylpropyl methylphosphonofluoridate (Soman) were tested, and the effects of Mn2+ and ethylenediamine tetraacetate (EDTA) on this activity. The plants are duckweed (Lemna minor), giant duckweed (Spirodela oligorhiza), and germinated mung bean (Vigna radiata); the protist is a slime mold (Dictyostelium discoidium). The tests are based on a crude classification of OPAAs as 'squid type' (DFP hydrolyzed more rapidly than Soman) and all of the others termed by us, with questionable justification, as 'Mazur type' (Soman hydrolyzed more rapidly than DFP). Of the two duckweeds, Spirodela oligorhiza hydrolyzes Soman but not DFP, and Lemna minor does not hydrolyze either substrate. In contrast to the report of Yu and Sakurai, mung bean does not hydrolyze DFP and hydrolyzes Soman with a 5-fold stimulation by Mn2+ and a marked inhibition by EDTA. The slime mold hydrolyzes Soman more rapidly than DFP (but does hydrolyze DFP) and the hydrolysis is Mn2+ stimulated. The failure of these plant sources to hydrolyze DFP is similar to the behavior of OPAA from Bacillus stearothermophilus.
Title: Degradation of nerve gases by CLECS and cells: kinetics of heterogenous systems Hoskin FC, Walker JE, Stote R Ref: Chemico-Biological Interactions, 119-120:439, 1999 : PubMed
We have reported the enzymatic hydrolysis of phosphoro- and phosphonofluoridates and phosphoro- and phosphonothiolates and -thionates by an organophosphorus hydrolase (OPH) from Pseudomonas diminuta. In screening for other microbial sources of nerve gas hydrolyzing enzymes, it would be convenient, indeed essential, to be able to determine such hydrolyses on intact cells. As a preliminary step to such screening we have measured the hydrolysis of O,O-diisopropyl S-(2-diisopropylaminoethyl) phosphorothiolate (Tetriso) and O,O-diethyl S-(2-ethylthioethyl) phosphorothiolate (Demeton-S; formerly Isosystox) by intact cells and sonicates. The purified OPH has also been cross-linked to itself (CLEC = cross-linked enzyme crystals) and this has also been tested for its ability to hydrolyze Tetriso and Demeton-S. The testing of such heterogenous systems by a spectrophotometric assay (Ellman) has required novel modifications. Our findings are that both Tetriso and Demeton-S are subject to intact-cell assay, that both are readily hydrolyzed by the CLEC-ed OPH without marked change in kinetics, but that at any given substrate concentration Tetriso is hydrolyzed much more rapidly. However, since Demeton-S is commercially available, this appears to be the substrate most suitable for screening for our final goal in a search for sources of enzymes to detoxify O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX).
Title: A closer look at the natural substrate for a nerve-gas hydrolyzing enzyme in squid nerve Hoskin FC, Walker JE Ref: Biological Bulletin, 195:197, 1998 : PubMed
Title: Malathion as a model for the enzymatic hydrolysis of the neurotoxic agent, VX Hoskin FC, Walker JE Ref: Bulletin of Environmental Contamination & Toxicology, 59:9, 1997 : PubMed
Title: Hydrolysis of tetriso by an enzyme derived from Pseudomonas diminuta as a model for the detoxication of O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) Hoskin FC, Walker JE, Dettbarn WD, Wild JR Ref: Biochemical Pharmacology, 49:711, 1995 : PubMed
An enzyme termed organophosphorus hydrolase (OPH), derived from Pseudomonas diminuta, had been found previously to hydrolyze the powerful acetylcholinesterase (AChE) inhibitor O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX). This enzyme has now been shown to be correlated with the loss of AChE inhibitory potency (detoxication). OPH also hydrolyzed and detoxified the VX analogue, O,O-diisopropyl S-(2-diisopropylaminoethyl) phosphorothiolate (Tetriso), also a potent AChE inhibitor, about five times faster than VX. The Km for the hydrolysis of the P-S bond of Tetriso was 6.7 x 10(-3) M. OPH also hydrolyzed diisopropylphosphorofluoridate (DFP) 50-60 times faster than Tetriso, and 1,2,2-trimethylpropyl methylphosphonofluoridate (Soman) about seven times faster than Tetriso. DFP was a non-competitive inhibitor of Tetriso hydrolysis, Ki = 8.7 x 10(-4) M. The DFP hydrolysis product, diisopropyl phosphate, was a competitive inhibitor, Ki = 2.3 x 10(-4) M. The rate of detoxication of Tetriso compared with the rate of hydrolysis suggests that OPH may not be totally specific for P-S bond cleavage. OPH was inhibited completely by 1.5 x 10(-4) M 8-hydroxyquinoline-5-sulfonate or 1,10-phenanthroline, both transition element chelators, but inhibited only partially by EDTA, a much more potent chelator.
Title: Enzymatic hydrolysis of tetriso as a model for the detoxication of the neurotoxic agent VX Hoskin FC, Walker JE Ref: Biological Bulletin, 187:249, 1994 : PubMed
When a nerve gas hydrolyzing enzyme [organophosphorus acid anhydrolase (OPAA), formerly DFPase] purified from squid hepatopancreas was injected into rabbits, the resulting sera (RAS) inhibited OPAA purified from either squid hepatopancreas or squid optic ganglia. The inhibition was non-competitive, with 50% inhibition at a 1:1,000 serum dilution, and with the limit of inhibition (in effect, a "titer") at approximately 1:10,000. This RAS did not inhibit the distinctly different OPAAs from a mammalian and two bacterial sources. The hepatopancreas-generated RAS also reacted positively to the appropriate enzyme-linked immunosorbent assay (ELISA) at a titer of 1:100,000. In marked contrast, when OPAA purified from squid optic ganglion was injected into rabbits, the resulting sera did not inhibit squid OPAA, and did not give a positive ELISA. Control sera taken from the same rabbits prior to any injection (RS) did not inhibit the OPAAs. These results show another major difference between squid type OPAAs and the OPAAs from other sources, sometimes termed "Mazur type" OPAAs.
Title: Stereoselectivity of soman detoxication by organophosphorus acid anhydrases from Escherichia coli Hoskin FC, Gallo BJ, Steeves DM, Walker JE Ref: Chemico-Biological Interactions, 87:269, 1993 : PubMed
Three organophosphorus acid anhydrases have been isolated from E. coli by gel filtration and ion exchange column procedures, and further identified by gel electrophoresis. All three have molecular weights in the 120,000-140,000 range. Two of them hydrolyze racemic 1,2,2-trimethylpropylmethylphosphonofluoridate (soman) to completion at a single rate and, in parallel with this, detoxify soman at a comparable rate. The third enzyme appears to show stereoselectivity with respect to the two pairs of isomers of soman in that it hydrolyzes the racemic mixture at a fast and a slow rate, the latter approaching the non-enzymatic rate, and detoxifies soman only at the slower rate. In the past, organophosphorus acid anhydrases from bacterial and mammalian sources have been assayed either as crude sonicates or homogenates, or as cold ethanol precipitated fractions. Major discrepancies among laboratories have probably been due either to the assay of mixtures of varying proportions of these three enzymes depending on the various organs or organisms used as the source, or to the purification of one of the enzymes at the expense of the others. For E. coli, a fourth organophosphorus acid anhydrase is also present but at a considerably lower activity.
Title: Biopolymer metal catalysts for the hydrolysis of nerve gases Hoskin FC, Rajan KS, Remy D, Walker JE Ref: Chemico-Biological Interactions, 87:109, 1993 : PubMed
Glucosamine oligomers--monomer through tetramer--form complexes with Cu2+ that catalyse the hydrolysis of the 'nerve gas' 1,2,2-trimethylpropyl- methylphosphonofluroidate (soman) by cleaving the P-F bond. A 1/1 glucosamine/Cu2+ ratio whether as glucosamine or glucosamine units, gives the highest hydrolytic rate over the 11.5/1 to 1/1 range. This trend also appears to hold for a glucosamine polymer, chitosan, which, when complexed with Cu2+ also hydrolyzes soman. The relatively low rate of hydrolysis by this polymer-Cu2+ complex, while not yet explainable, is consistent with an extrapolation of the monomer-through-tetramer series. The question may be raised as to whether these biopolymer metal complexes provide any clues to the involvement of Mn2+ in the functioning of one class of P-F cleaving enzymes.
Title: Genetic and biochemical evidence for the lack of significant hydrolysis of soman by a Flavobacterium parathion hydrolase Pogell BM, Rowland SS, Steinmann KE, Speedie MK, Hoskin FC Ref: Applied Environmental Microbiology, 57:610, 1991 : PubMed
Pure recombinant Flavobacterium parathion hydrolase (an organophosphorus acid anhydrase) from Streptomyces lividans was found to hydrolyze the toxic nerve agent soman at only 0.1% of the rate observed with parathion as substrate. Studies with wild-type and recombinant strains of S. lividans support the lack of significant soman breakdown by the hydrolase and also indicate the presence in S. lividans of other significant hydrolytic enzymatic activity towards soman.
An enzyme that hydrolyzes soman (1,2,2-trimethylpropyl methylphosphonofluoridate) and two other phosphonofluoridates, but does not hydrolyze DFP (diisopropylphosphorofluoridate), has been partially purified from a rod-shaped spore-forming gram-positive OT (obligate thermophilic) bacterium. The enzyme shows a marked Mn2+ stimulation, and in this and its substrate preference does not resemble the organophosphorus acid anhydrolase (sometimes termed DFPase) found in squid. Like the squid enzyme, it is not inhibited by mipafox (N,N'-diisopropylphosphordiamidofluoridate), is not inactivated by ammonium sulfate, and does hydrolyze the acetylcholinesterase-inhibitory pair of diastereoisomers of soman as well as the relatively noninhibitory pair, thus detoxifying soman. In these three properties the OT enzyme does not resemble the ubiquitous organophosphorus acid anhydrolase often purified from mammalian and bacterial sources by cold ethanol fractionation. Thus this phosphono-specific OT enzyme may have a natural substrate and a physiological role distinct from other organophosphorus acid anhydrolases.
Title: The new format Hoskin FC Ref: Science, 231:536, 1986 : PubMed
Title: Inhibition of a soman- and diisopropyl phosphorofluoridate (DFP)-detoxifying enzyme by Mipafox Hoskin FC Ref: Biochemical Pharmacology, 34:2069, 1985 : PubMed
Mipafox, N,N'-diisopropylphosphordiamidofluoridate, has been found to be a reversible competitive inhibitor of a diisopropyl phosphorofluoridate hydrolyzing enzyme (DFPase) isolated from hog kidney and Escherichia coli. Heretofore, this DFPase was characterized by its more rapid hydrolysis of Soman (1,2,2-trimethylpropyl methylphosphonofluoridate), its stimulation by Mn2+, and its wide distribution. In sharp contrast, Mipafox did not inhibit the DFPase found only in cephalopod nerve, hepatopancreas, and saliva, and further characterized by its more rapid hydrolysis of DFP than of Soman, and its indifference to Mn2+. Neither of these two DFPases hydrolyzed Mipafox.
Title: An organofluorophosphate-hydrolyzing activity in Tetrahymena thermophila Landis WG, Savage RE, Jr., Hoskin FC Ref: J Protozool, 32:517, 1985 : PubMed
An enzymatic activity that hydrolyzes O,O-diisoproplyphosphofluoridate (DFP) and O-1,2,2-trimethylpropylmethylphosphonofluoridate (Soman) was discovered in the ciliate protozoan Tetrahymena thermophila. The enzymatic activity classifies the protein as Mazur-type similar to that found in hog kidney and Escherichia coli. The rate of hydrolysis of Soman by the Tetrahymena-extract is the highest, on a per gram of extract basis, of any eucaryote. The molecular weight is approximately 75,400 as determined by Sephacryl column chromatography. A maximum fifteen-fold purification has been achieved. Potential exists for the detoxification and one-step detection of common organofluorophosphate pollutants. Additionally, Tetrahymena should prove an easier subject for manipulation than mammalian or squid sources. Protozoa may be a potentially important source of detoxification and degradation enzymes for other environmental contaminants.
Title: Two enzymes for the detoxication of organophosphorus compounds--sources, similarities, and significance Hoskin FC, Kirkish MA, Steinmann KE Ref: Fundamental & Applied Toxicology, 4:S165, 1984 : PubMed
An enzyme in E. coli that hydrolyzes diisopropylphosphorofluoridate (DFP) has now been found to hydrolyze the nerve gas 1,2,2- trimethylpropylmethylphosphonofluoridate (soman) many times faster. With either substrate the E. coli enzyme is stimulated manyfold by 10(-3) M Mn2+. These criteria are combined and applied to this, and to a superficially similar but distinctly different, enzyme found in squid nerve. The results suggest that while several tissues of the squid contain only this second kind of DFP hydrolyzing enzyme, termed squid type DFPase , many other sources including E. coli contain a mixture of squid type DFPase (the name not strictly indicative of source) and the other DFP hydrolyzing enzyme, now termed Mazur type DFPase . Procedures for the purification of Mazur type DFPase from hog kidney, while increasing the specific activity for DFP hydrolysis may actually have been enriching the purified material in the squid type DFPase . Because E. coli has the highest soman hydrolyzing capacity of any source so far examined, this organism is a promising source for the development of new purification procedures for Mazur type DFPase .
Title: Characterization of a DFP-hydrolyzing enzyme in squid posterior salivary gland by use of Soman, DFP and manganous ion Hoskin FC, Prusch RD Ref: Comparative Biochemistry & Physiology C Pharmacol Toxicol, 75:17, 1983 : PubMed
1. A phosphorus-fluorine splitting enzyme (DFPase) from squid nerve hydrolyzes DFP 5-10 times faster than it hydrolyzes another P-F compound, Soman, whereas a superficially similar enzyme from rat kidney hydrolyzes Soman 20-40 times faster than it hydrolyzes DFP, all under comparable conditions. 2. The DFPase from rat kidney is stimulated 2- to 3-fold by 4 X 10(-4) M Mn2+, whereas the DFPase from squid nerve is unaffected or slightly inhibited by 4 X 10(-4) M Mn2+. 3. These observations form the basis for distinguishing between a squid type DFPase and a mammalian DFPase, the names not being rigorously indicative of enzyme source or substrate. 4. When these criteria are applied to a P-F splitting enzyme found in squid saliva, the enzyme is identifiable as squid type DFPase. There is a significantly higher level of this enzyme in whole saliva from female squids than in whole saliva from male squids. This squid type DFPase is different from the proteinous toxin also found in squid saliva.
Title: Hydrolysis of nerve gas by squid-type diisopropyl phosphorofluoridate hydrolyzing enzyme on agarose resin Hoskin FC, Roush AH Ref: Science, 215:1255, 1982 : PubMed
An enzyme purified from squid nerve that hydrolyzes the cholinesterase inhibitor diisopropyl phosphorofluoridate (DFP) has now been coupled to agarose beads. A column of this agarose-DFPase hydrolyzes the nerve gas 1,2,2-trimethylpropyl methylphosphonofluoridate (Soman). Although the more inhibitory of the four diastereoisomers of Soman are hydrolyzed least rapidly, a column of sufficient length will accomplish 95 percent hydrolysis whether measured by fluoride release or loss of cholinesterase-inhibiting power. The results suggest a means for detoxifying unwanted chemical warfare agents.
Title: Penetration of VX into nerve cells, and effects on electrical function Farquharson DA, Hoskin FC, Hubbard K, Prusch RD Ref: Bulletin of Environmental Contamination & Toxicology, 24:719, 1980 : PubMed
Title: Stereospecificity and active site requirements in a diisopropylphosphorofluoridate-hydrolyzing enzyme Gay DD, Hoskin FC Ref: Biochemical Pharmacology, 28:1259, 1979 : PubMed
Title: Soman and receptor-ligand interaction in Electrophorus electroplaques Bullock JO, Farquharson DA, Hoskin FC Ref: Biochemical Pharmacology, 26:337, 1977 : PubMed
Title: Hydrogen sulfide as a precursor for the synthesis of isethionate in the squid giant axon Hoskin FC, Kordik ER Ref: Archives of Biochemistry & Biophysics, 180:583, 1977 : PubMed
Title: Distribution of diisopropylphosphorofluoridate-hydrolyzing enzyme between sheath and axoplasm of squid giant axon Hoskin FC Ref: Journal of Neurochemistry, 26:1043, 1976 : PubMed
Title: Toxicity of DFP and related compounds to squids in relation to cholinesterase inhibition and detoxifying enzyme levels Dettbarn WD, Hoskin FC Ref: Bulletin of Environmental Contamination & Toxicology, 13:133, 1975 : PubMed
Title: Comparison of DFP-hydrolyzing enzyme purified from head ganglion and hepatopancreas of squid (Loligo pealei) by means of isoelectric focusing Garden JM, Hause SK, Hoskin FC, Roush AH Ref: Comparative Biochemistry & Physiology C Pharmacol Toxicol, 52:95, 1975 : PubMed
Title: An improved method for the measurement of 14CO2 applied to a problem of cysteine metabolism in squid nerve Hoskin FC, Pollock ML, Prusch RD Ref: Journal of Neurochemistry, 25:445, 1975 : PubMed
Title: An improved sulphur assay applied to a problem of isethionate metabolism in squid axon and other nerves Hoskin FC, Brande M Ref: Journal of Neurochemistry, 20:1317, 1973 : PubMed
Title: The effects of pH on penetration and action of procaine 14C, atropine 3H, n-butanol 14C and halothane 14C in single giant axons of the squid Dettbarn WD, Heilbronn E, Hoskin FC, Kitz RJ Ref: Neuropharmacology, 11:727, 1972 : PubMed
Title: Purification of a DFP-hydrolyzing enzyme from squid head ganglion Hoskin FC, Long RJ Ref: Archives of Biochemistry & Biophysics, 150:548, 1972 : PubMed
Squid nerve contains an enzyme that hydrolyzes the nerve gas Tabun at about one-tenth the rate it hydrolyzes diisopropylphosphorofluoridate (DFP), and at about one-third to one-fourth the rate it hydrolyzes Sarin and Soman. Tabun is a more potent inhibitor of acetylcholinesterase than is DFP, is both lipid-and water-soluble, and penetrates readily into the squid giant axon in its inhibitory form. The failure of Tabun to block or markedly decrease the conducted action potential in the squid axon makes it likely that the blocking of conduction caused by DFP is probably not due to inhibition of acetylcholinesterase. Sub-strate specificity with regard to organophosphate metabolism by squid enzyme has possible implications for the disposal and detoxication of nerve gases in the ocean.
Title: Spontaneous reactivation of organophosphorus-inhibited electroplax cholinesterase in relation to acetylcholine-induced depolarization Dettbarn WD, Bartels E, Hoskin FC, Welsch F Ref: Biochemical Pharmacology, 19:2949, 1970 : PubMed
Title: Effects of some cholinesterase inhibitors on the squid giant axon. Their permeability, detoxication and effects on conduction and acetylcholinesterase activity Hoskin FC, Kremzner LT, Rosenberg P Ref: Biochemical Pharmacology, 18:1727, 1969 : PubMed
Title: The effects of cyclopropane and diethyl ether on tissue oxygen consumption and anaerobic glycolysis of brain in vitro Matteo RS, Hoech GP, Jr., Hoskin FC Ref: Anesthesiology, 30:156, 1969 : PubMed
Title: Metabolism of specifically labelled glucose by explants of newborn mouse cerebellum Hoskin FC, Allerand CD Ref: Journal of Neurochemistry, 15:427, 1968 : PubMed
Title: Penetration of an organophosphorus compound into squid axon and its effects on metabolism and function Hoskin FC, Rosenberg P Ref: Science, 156:966, 1967 : PubMed
The tertiary analogute of phospholine, namely, (C(2)H(5)O)(2)P(O)SCH(2)CH(2)N(CH(3))(2), is a potent, irreversible inhibitor of cholinesterase which, when externally applied to the sqluid giant axon, readily penetrates in its inhibitory form into the axoplasm. However, even a 10(-2) molar solution of this compound does not block axonal conduction unless the axon is first treated with a low concentration of venom from the cottonmouth moccasin. The question of the activity of acetylcholinesterase in these axons is considered, and the possibility of subcellular permeability barriers for indivisual components of the excitable membrane is discussed.
Title: Anaerobic glycolysis in parts of the giant axon of squid Hoskin FC Ref: Nature, 210:856, 1966 : PubMed
Title: Re-examination of the effect of DFP on electrical and cholinesterase activity of squid giant axon Hoskin FC, Rosenberg P, Brzin M Ref: Proc Natl Acad Sci U S A, 55:1231, 1966 : PubMed
Title: Penetration of sugars, steroids, amino acids, and other organic compounds into the interior of the squid giant axon Hoskin FC, Rosenberg P Ref: Journal of General Physiology, 49:47, 1965 : PubMed
Squid axons were exposed to solutions of C(14)-labeled compounds. After 60 minutes the axoplasm was extruded and assayed for radioactivity. The following compounds penetrated to about 3 per cent of what would have been expected had there been no barrier to free diffusion and the subsequent attainment of equivalent distribution: mannitol, sucrose, glutamate, glutamine, aspartate, 3,4-dihydroxyphenylalanine, 3,4-dihydroxyphenylethylamine, lambda-aminobutyrate, serotonin, and dehydroepiandrosterone sulfate. All these compounds are water-soluble; in addition, some are ionized over the entire pH range. Partially ionized indoleacetate, acetylsalicylate, and 5,5-diphenylhydantoin penetrated about 40 per cent and unionized, water-insoluble cortisol and dieldrin, 100 per cent. A striking exception to this grouping was glucose, which penetrated about 20 per cent. Studies with specifically labeled glucose indicate participation of the pentose phosphate pathway as a metabolic route in axonal membrane and associated cell wall material, and partial or complete absence of the oxidative system in the axoplasm. Except for glucose, penetration of the substances studied appears to depend largely on the extent of the non-polar, lipophilic character of the compound. Penetration can be markedly increased by pretreatment of the axons with cottonmouth moccasin venom.
Title: Penetration of acetylcholine into squid giant axons Rosenberg P, Hoskin FC Ref: Biochemical Pharmacology, 14:1765, 1965 : PubMed
Title: Stimulation of respiration and inhibition of glycolysis in lobster axons by menadione and some naphthoquinones Hoskin FC Ref: Archives of Biochemistry & Biophysics, 108:506, 1964 : PubMed
Title: ALTERATION OF ACETYLCHOLINE PENETRATION INTO, AND EFFECTS ON, VENOM-TREATED SQUID AXONS BY PHYSOSTIGMINE AND RELATED COMPOUNDS Hoskin FC, Rosenberg P Ref: Journal of General Physiology, 47:1117, 1964 : PubMed
Choline and neostigmine markedly antagonize the effect of acetylcholine (ACh) on the action potential of the venom-treated squid axon, although they themselves have no effect on conduction. Physostigmine also antagonizes the blocking action of ACh at a concentration well below that which has any effect on conduction. In contrast, d-tubocurarine (curare) increases the effect of ACh on the action potential. Choline, neostigmine, and physostigmine markedly decrease the penetration of C(14)-labeled ACh into the axoplasm of the squid axon. Curare, in contrast, increases the penetration of ACh, whereas dimethylcurare gives variable results. The results provide an explanation why physostigmine and neostigmine do not influence the action of ACh on axonal conduction in a way similar to that observed at the junction. The additive effect of curare and ACh on the action potential may be due either to the greater rate of penetration of ACh or to an additive effect of the two compounds on the receptor, or to a combination of both factors.
Title: Stereospecificity in the reactions of acetylcholinesterase Hoskin FC Ref: Proceedings of the Society for Experimental Biology & Medicine, 113:320, 1963 : PubMed
Title: Demonstration of increased permeability as a factor in the effect of acetylcholine on the electrical activty of venom-treated axons Rosenberg P, Hoskin FC Ref: Journal of General Physiology, 46:1065, 1963 : PubMed
D-Tubocurarine (curare) and acetylcholine (ACh) had been found to block electrical activity after treatment of squid giant axons with cottonmouth moccasin venom at a concentration which had no effect on conduction. It has now been demonstrated that this effect is attributable to reduction of permeability barriers. The penetration of externally applied C(14)-labeled dimethylcurare, ACh, choline, and trimethylamine into the axoplasm of the squid giant axon was determined in axons treated with either cottonmouth, rattlesnake, or bee venom, and in untreated control axons. The lipid-soluble tertiary nitrogen compound trimethylamine readily penetrated into the axoplasm of untreated axons. In contrast, after exposure of the axons to the lipid-insoluble quaternary nitrogen compounds for 1 hour their presence in the axoplasm was hardly detectable (less than 1 per cent). However, following 15microg/ml cottonmouth venom 1 to 5 per cent of their external concentration is found within the axoplasm while following 50microg/ml venom 10 to 50 per cent enters. The penetration of dimethylcurare is also increased by 10 microg/ml bee venom but not by 1 microg/ml bee venom nor 1000 microg/ml rattlesnake venom. The experiments show that when ACh and curare, following venom treatment, affect electrical activity, they also penetrate into the axon. Treatments which do not increase penetration are also ineffective in rendering the compounds active.
Title: Electrical and esterase activity in axons Dettbarn WD, Hoskin FC Ref: Biochimica & Biophysica Acta, 62:566, 1962 : PubMed
Title: Specificity of the stimulation by quinones of direct oxidation of glucose by brain slices Hoskin FC Ref: Biochimica & Biophysica Acta, 62:11, 1962 : PubMed
Title: Effect of inhibitors on the metabolism of specifically labelled glucose by brain Hoskin FC Ref: Biochimica & Biophysica Acta, 40:309, 1960 : PubMed
Title: A source of error in the use of radioactive substrates for metabolic studies Hoskin FC Ref: Archives of Biochemistry & Biophysics, 87:151, 1960 : PubMed
Title: Intermediate metabolism of electric tissue in relation to function. II. Comparison of glycolysis rates in organs of Electrophorus electricus Hoskin FC Ref: Archives of Biochemistry & Biophysics, 81:330, 1959 : PubMed
Title: Intermediate metabolism of electric tissue in relation to function. III. Oxidation of substances by tissues of Electrophorus electricus as compared to other vertebrates Hoskin FC Ref: Archives of Biochemistry & Biophysics, 85:141, 1959 : PubMed
Title: Kinetics of the enzymatic hydrolyses of sarin Adie PA, Hoskin FC, Trick GS Ref: Canadian Journal of Biochemistry & Physiology, 34:80, 1956 : PubMed
Title: Some observations concerning the biochemical inertness of methylphosphonic and isopropyl methylphosphonic acids Hoskin FC Ref: Canadian Journal of Biochemistry & Physiology, 34:743, 1956 : PubMed
Title: Stereospecificity in the enzymatic hydrolyses of tabun and acetyl-methylcholine chloride Hoskin FC, Trick GS Ref: Canadian Journal of Biochemistry & Physiology, 33:963, 1955 : PubMed
Title: Stereospecificity in the enzymatic hydrolyses of tabun and acetyl-beta-methylcholine chloride Hoskin FC, Trick GS Ref: Canadian Journal of Biochemistry, 34:75, 1955 : PubMed
