NDLI: Mechanism of the reaction of papain with substrate-derived diazomethyl ketones. Implications for the difference in site specificity of halomethyl ketones for serine proteinases and cysteine proteinases and for stereoelectronic requirements in the papain catalytic mechanism.

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Mechanism of the reaction of papain with substrate-derived diazomethyl ketones. Implications for the difference in site specificity of halomethyl ketones for serine proteinases and cysteine proteinases and for stereoelectronic requirements in the papain catalytic mechanism.

Content Provider	Semantic Scholar
Author	Brocklehurst, Keith Malthouse, J. Paul G.
Copyright Year	1978
Abstract	The reactions of papain (EC 3.4.22.2) with substrate-derived diazomethyl ketones reported by Leary, Larsen, Watanabe & Shaw [Biochemistry (1977) 16, 5857--5861] are unusual in that (i) these reagents fail to react with low-molecular-weight thiols and (ii) the rate of reaction with the papain thiol group does not decrease to near-zero values across a pKa of 4 as the pH is decreased. Existing data are shown to suggest an interpretation involving neighbouring-group participation via transient thiohemiketal formation, rate-determining protonation by imidazolium ion and alkylation on sulphur via a three-membered cyclic transition state. Implications for (a) the difference in site-specificity exhibited by halomethyl ketones in their reactions with serine proteinases and cysteine proteinases and (b) stereoelectronic requirements in the mechanism of papain-catalysed hydrolysis are discussed. The possibility of two tetrahedral intermediates between adsorptive complex and acyl-enzyme is indicated.
File Format	PDF HTM / HTML
DOI	10.1042/bj1750761
PubMed reference number	743223
Journal	Medline
Volume Number	175
Issue Number	2
Alternate Webpage(s)	http://www.biochemj.org/content/ppbiochemj/175/2/761.full.pdf
Alternate Webpage(s)	https://doi.org/10.1042/bj1750761
Journal	The Biochemical journal
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article

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