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. 1966 May;99(2):275–282. doi: 10.1042/bj0990275

The α-chymotryptic hydrolysis of glycine esters

D W Ingles 1, J R Knowles 1
PMCID: PMC1264994  PMID: 5944238

Abstract

1. The α-chymotrypsin-catalysed hydrolysis of N-acetylglycine ethyl and thiolethyl esters was investigated at pH7·90 and 25° over a wide range of substrate concentrations. 2. The Lineweaver–Burk plots for these substrates are markedly curved, and it is shown that the curvature is due solely to the `enzyme-blank' reaction. The rate of this reaction is proportional to free enzyme concentration in the range 10–100μm, with a pseudo-first-order rate constant of approx. 1×10−3sec.−1. Correction for this reaction by the procedure described leads to linear plots. It is shown that the significance of the enzyme-blank reaction depends on the value of k0/Km for the substrate under investigation. 3. Interpretation of the curvature in the Lineweaver–Burk plots by previous workers in terms of activation by excess of substrate is shown to be erroneous. 4. Values of Km 387mm and k0 0·039sec.−1, and Km 41mm and k0 0·23sec.−1, were obtained for the ethyl and thiolethyl esters of N-acetylglycine respectively. The literature values for the methyl esters of N-acetyl- and N-propionyl-glycine have been corrected by the procedure described. The new values agree much better with current theories of α-chymotrypsin mechanism and specificity. 5. The kinetic parameters for the ethyl and thiolethyl esters indicate the absence of an electrophilic component in the catalytic mechanism of α-chymotrypsin, and the importance of the ester function in substrate binding.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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