Non-Competitive Inhibition of Flyhead Acetylcholinesterase by Oxime Carbamates. Kinetic Evidence for Non-productive Binding to the Catalytic Site

Reversible inhibition of flyhead acetylcholinesterase (E. C. 3.1.1.7) by two oxime carbamates possessing large N-substituents (isopropyl and allyl) was found to follow competitive kinetics of a biphasic nature with acetylcholine as the substrate. The derived values for the substrate dissociation constants of high and low affinity were in approximate agreement with the Michaelis and the non-competitive substrate inhibition constant for acetylcholine respectively. Data for the dependence of carbamoylation rates of the enzyme upon substrate concentration did not agree with a model derived from reversible inhibition kinetics. Reversible inhibition studies indicated low active site competitive inhibition constants, showing good binding to the active site. Studies upon the carbamoylation rates indicated (i) a non competitive interaction, (ii) very low concentrations of a reversibly-formed enzyme/carbamate complex prior to carbamoylation of the active site. A possible explanation for the discrepancy is discussed whereby a reversible Ki determined from inhibition rate saturation by a »Main plot« measures the concentration of carbamate aligned in the active site following an induced shift of enzyme conformation, whereas competitive inhibition constants (Ki) determined from reversible inhibition experiments determine all binding modes at the active site which interfere with substrate attachment. Carbamates with large N-substituents show this effect more because overlap of the carbamoyl moiety with the catalytic site is less likely due to steric hinderance

Mitochondrial complex I and cell death: a semi-automatic shotgun model

Mitochondrial dysfunction often leads to cell death and disease. We can now draw correlations between the dysfunction of one of the most important mitochondrial enzymes, NADH:ubiquinone reductase or complex I, and its structural organization thanks to the recent advances in the X-ray structure of its bacterial homologs. The new structural information on bacterial complex I provide essential clues to finally understand how complex I may work. However, the same information remains difficult to interpret for many scientists working on mitochondrial complex I from different angles, especially in the field of cell death. Here, we present a novel way of interpreting the bacterial structural information in accessible terms. On the basis of the analogy to semi-automatic shotguns, we propose a novel functional model that incorporates recent structural information with previous evidence derived from studies on mitochondrial diseases, as well as functional bioenergetics

Antigastra catalaunalis (Duponchel) in north Kent

Volume: 89Start Page: 10End Page: 1