Photosuicide inactivation of acetylcholinesterase by nitrosamine derivatives

Protein ligand interactions. Part 5: Isoquinoline alkaloids as inhibitors of acetylcholinesterase from Electrophorus electricus

Kinetic analysis has shown that papaverine, berberine and isoquinoline alkaloids acts as reversible competitive inhibitors of acetylcholinesterase with respect to the substrate, acetylthiocholine chloride. The inhibitor constants (Ki) vary from 3.5 microM to 88 microM. With time they act as irreversible covalent inhibitors with papaverine producing 85% inactivation after 40 min. Pseudo first-order kinetics are observed with the rate constant being proportional to the concentration of the ligand and the order of reaction being equal to one. Spectrophotometry was used to study the binding of the ligands with acetylcholinesterase and Scatchard analysis used to calculate the respective dissociation constants and the number of binding sites.

Interaction and inhibition of acetylcholinesterase from Electrophorus electricus by nitrosamines

Kinetic analysis has shown that dimethylnitrosamine, dipropylnitrosamine, dibutylnitrosamine, and diphenylnitrosamine initially act as reversible competitive inhibitors with respect to the substrate, acetylthiocholine chloride. The inhibitor constants Ki vary from 21-30 microM for the aliphatic nitrosamines to 8.2 microM for the aromatic diphenylnitrosamine. With time they act as irreversible covalent inhibitors with dimethylnitrosamine producing 82% inactivation after 40 min. Pseudo-first-order kinetics are observed with the rate constant being proportional to the concentration of the nitrosamine and the order of reaction being equal to one. Fluorometry, gel chromatography, and equilibrium dialysis have been used to study the binding of the nitrosamines with acetylcholinesterase. Scatchard analysis indicates that dimethyl-, dipropyl-, and dibutylnitrosamine have a weaker affinity for the enzyme (Kd 5.6-8.08 microM) compared to diphenylnitrosamine (Kd 2.32 microM). In all cases the number of binding sites was four.

Protein-ligand interactions: interaction of nitrosamines with nicotinic acetylcholine receptor

Fluorimetry and spectrophotometry have been used to study the binding of dimethyl, dipropyl, dibutyl and diphenylnitrosamine to nicotinic acetylcholine receptor isolated, and purified, from Torpedo fuscomaculata. Scatchard analysis indicates that all four ligands are true agonists of the receptor exhibiting positive cooperative binding with the existence of more than one class of binding site. The number of binding sites for the nitrosamines approximates 2. Diphenylnitrosamine binds to the receptor more tightly at low concentrations (Kd1 = 1.3 microM) than the aliphatic nitrosamine (Kd1 = 8-12 microM). Yet at high concentrations all nitrosamines behaved with similar Kd values (27-38 microM).

Recent developments in inhibiting cysteine and serine proteases

Some 20 years ago, affinity labelling was introduced to help gather information on active-site catalytic groups and the mechanisms of proteolytic enzymes. Now this knowledge is used to produce specific and selective inhibitors for these enzymes. The concept of "biospecific drug design" has stimulated progress in turning the inhibitors into therapeutically applicable agents. For instance, sales of antihypertensive drugs based on inhibitors of the angiotensin converting enzyme are expected to be over 2 billion US-$ in 1992. This partly illustrates the efforts made by many researchers to introduce strategies in potease inhibition for medicinal purposes. This review discusses some of the concepts.

Biochemical effects and monitoring of exposure of rats to 4-methylcyclohexyl-1,6-dicarboxylic acid anhydride vapour

Male Wistar rats exposed to 5, 10 or 20 p.p.m. 4-methylcyclohexyl-1,6-dicarboxylic acid anhydride vapour for 2-11 weeks showed dose-dependent blood anhydride concentrations. The maximum concentrations were found after two weeks. At five exposure weeks, they were smaller but they did not decrease further thereafter. The change was coincident with increased epoxide hydrase activity in liver. The excretion of 4-methylcyclohexyl-1,6-dicarboxylic acid was detected in the urine. The excretion was linearly related to the exposure in specimens collected during the 10th and 11th week. Brain acetylcholinesterase activity was transiently inhibited by the exposure at the two higher doses while decreased enzyme activity in the isolated spinal cord axons was only found after 11 weeks. This change was simultaneous with increased creatine kinase activity in the cerebellar homogenate. In the occupational setting, acetylcholinesterase activity might only be significantly inhibited in lungs because of the low exposure levels.

Influence of the carboxylesterase inhibitor bis-p-nitrophenylphosphate on the rates of hydrolysis of various alpha-esters of 1-(N-methyl-N-nitrosamino)-methanol in vitro and in vivo and on the acute toxicity and carcinogenicity of 1-(N-methyl-N-nitrosamino)-methylacetate

The effect of an in vivo treatment with the carboxylesterase inhibitor bis-p-nitrophenylphosphate (BNPP) on the hydrolysis of 1-(N-methyl-N-nitrosamino)-methylacetate (NNMA), 1-(N-methyl-N-nitrosamino)-methylbutyrate (NNMB), 1-(N-methyl-N-nitrosamino)-methylbenzoate (NNMBz) and 1-(N-methyl-N-nitrosamino)-methylpivaloate (NMMP) in rat tissue homogenates was studied. The rates of hydrolysis were specific for each compound and different in every organ tested; the extent of inhibition of the hydrolysis by BNPP was also substrate and organ specific. In some cases no inhibition at all was observed. The rate of elimination of NNMA, NNMB, and NNMP from blood was not influenced by BNPP pretreatment. The LD50 of NNMA after i.v. application showed a rise of 85% with a BNPP pretreatment. BNPP also influenced the carcinogenicity of NNMA, whereby the total carcinogenic potency was not altered, but the organotropism had changed slightly.