Evidence that the active centre of chymopapain A is different from the active centres of some other cysteine proteinases and that the Brønsted coefficient (βnuc.) for the reactions of thiolate anions with 2,2′-dipyridyl disulphide may be decreased by reagent protonation
- 1 July 1980
- journal article
- research article
- Published by Portland Press Ltd. in Biochemical Journal
- Vol. 189 (1) , 189-192
- https://doi.org/10.1042/bj1890189
Abstract
The active centers of chymopapains A and B (jointly designated EC 3.4.22.6) and papaya (Carica papaya L.) peptidase A were investigated by using 2,2''-dipyridyl disulfide and 5,5''-dithiobis-(2-nitrobenzoic acid) as thiol-specific reactivity probes. Whereas the first active-center pKa values for chymopapain B and papaya peptidase A are less than 5, as is the case for papain (EC 3.4.22.2) and ficin (EC 3.4.22.3), that for chymopapain A is about 6.8. The reason why the reactions of thiols of pKa approximately 6.5 with 2.2''-dipyridyl disulfide are essentially pH-independent in the pH range around the thiol pKa is delineated. The value of the Bronsted coefficient (.beta.nuc.) for the reactions of thiolate ions with the 2,2''-dipyridyl disulfide monocation appears to be smaller than its value for the corresponding reactions with the neutral disulfide.This publication has 9 references indexed in Scilit:
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