Acetylcholinesterase Substrates: β-Methylcholine Esters

Steinberg, George M.; Mednick, Morton L.; Rice, Robert E.; Maddox, Jan P.

doi:10.1002/jps.2600590809

Cited by 5 publications

(2 citation statements)

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“…1 order of magnitude greater than those for comparable uncharged species (Eigen, 1964); therefore, a more slowly reacting positively charged substrate for the enzyme was sought as a control for the cationic AcSCh. The low value of kCM/Km reported by Steinberg et al (1970) of 6 X 106 M"1 s-1 for propionyl-/3-methylcholine, which is a factor of ca. 10 less than that reported by them for AcCh, suggested the former as a likely candidate for the desired chemically controlled substrate.…”

Section: Resultsmentioning

confidence: 78%

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Fractional diffusion-limited component of reactions catalyzed by acetylcholinesterase

Bazelyansky¹,

Robey²,

Kirsch³

1986

Biochemistry

143

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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.

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Section: Resultsmentioning

confidence: 78%

“…It was dissolved in 0.1 M NaCl-0.05 M sodium phosphate buffer, pH 7.5, and stored in the freezer at -10 °C. The values of kQ;it/Km typically obtained with commercial enzyme preparations (Steinberg et al, 1970;Hasan et al, 1980;Naveh et al, 1981) are ca. one-fifth that measured with fresh preparations (Rosenberry, 1975).…”

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confidence: 99%