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PMID:3954986

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Citation

Bazelyansky, M, Robey, E and Kirsch, JF (1986) Fractional diffusion-limited component of reactions catalyzed by acetylcholinesterase. Biochemistry 25:125-30

Abstract

The values of kcat/Km for the reactions of four substrates, p-nitrophenyl acetate (PNPA), propionyl-beta-methylthiocholine (PrMSCh), 3,3-dimethylbutyl thioacetate (DBTA), and acetylthiocholine (AcSCh), with acetylcholinesterase were determined as a function of increasing viscosity (eta rel) in sucrose-containing and in glycerol-containing buffers. Glycerol, or possibly some contaminant of it, was found to be a nonspecific inhibitor and sucrose a nonspecific activator of the enzyme as reflected in the dependence of kcat/Km values measured for PNPA and PrMSCh upon the concentration of these reagents. The rates of reactions of these two substrates, the first neutral and the second cationic, are chemically limited rather than diffusion limited, and they thus serve as quantitative controls or internal standards to monitor the effects of the viscosogens on the enzyme, which are not related to diffusion. The additional effect on kcat/Km over the controls observed for the rapidly reacting substrates AcSCh (cationic) and DBTA (neutral) serves as a measure of the extent to which these values of kcat/Km measure diffusion-controlled processes. The reaction rate of DBTA with the enzyme is 24% diffusion controlled as measured in glycerol-containing buffers and 16-20% as determined in sucrose-containing buffers, while that for AcSCh is 100% (in glycerol) and 24-40% (in sucrose) diffusion controlled.

Links

PubMed

Keywords

Acetylcholinesterase/metabolism; Animals; Buffers; Diffusion; Electrophorus; Enzyme Activation; Kinetics; Mathematics; Substrate Specificity; Viscosity

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

HUMAN:ACES

enables

GO:0017171: serine hydrolase activity

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete


See also

References

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