2 reference(s) found. Listing paper details in reverse chronological order. We are grateful to Keith Bradnam for improvment of this script
Title: Degradation by rat tissues in vitro of organophosphorus esters which inhibit cholinesterase Pla A, Johnson MK Ref: Biochemical Pharmacology, 38:1527, 1989 : PubMed
Hydrolytic "A"-esterase activities of various tissues of rat (plasma, liver, kidney, brain and intestinal mucosa) against selected OP esters of diverse structure as potential substrates (paraoxon, di-n-propyl paraoxon, di-n-butyl paraoxon, chlorpyrifos oxon, di-(4-phenyl butyl) phosphorofluoridate and the chiral isomers of ethyl 4-nitrophenyl phenylphosphonate) were studied. We have developed a sensitive and widely applicable assay depending on measuring decline in residual inhibitory power of any chosen OP against horse serum cholinesterase: for seven compounds examined so far I50s against BCHE ranged from 0.07 to 70 nM, and it is easy to monitor loss of OP starting from an initial 25 microM concentration. Progressive destruction rates were always highest in liver and plasma with activity sometimes detectable in kidney, brain but not in intestinal mucosa, but the ratios of activity between tissues differed for different substrates. At 25 microM/37 degrees/pH 7.2 hydrolysis rates ranged from 8500 nmol/min/g liver for di-(4-phenylbutyl) phosphorofluoridate down to 0.8 nmol/min for the butyl analogue of paraoxon; the rate for L(-) isomer of EPN oxon (23 nmol/min/g liver) was greater than 2x that for the D(+) isomer and for paraoxon. From our data we conclude that several OP hydrolases exist whose identity may be further characterised by use of selective substrates
Title: Enhancement of the binding of O-ethyl O-p-nitrophenyl phenylphosphonate (EPNoxon) to microsomal carboxylesterase by NAD in vitro Sugiyama S, Hosokawa M, Igarashi T, Ueno K, Satoh T, Kitagawa H Ref: Japanese Journal of Pharmacology, 37:39, 1985 : PubMed
Inhibition of rat liver microsomal carboxylesterase (CEase) by O-ethyl O-p-nitrophenyl phenylphosphonothioate (EPN) and binding of EPN oxygen analog to microsomal CEase were enhanced by addition of NAD or NADP. This was more prominent in addition of NAD than NADP. No potentiation of anti-CEase action of EPN by NAD was seen when pure esterase (E.C. 3.1.1.1) instead of liver microsomes was used as an enzyme source. This effect of NAD in microsomal CEase was significantly decreased when N-ethylmaleimide or p-chloromercuribenzoic acid was added. From these findings, it is strongly suggested that NAD-mediated potentiation of the anti-CEase action of EPN might be attributed to the increase in formation of NADH from NAD by microsomal dehydrogenase(s) containing a sulfhydryl group, leading to a subsequent increase in formation of the EPN oxygen analog from EPN, and in turn, CEase inhibition was enhanced.
