These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Evidence that the active centre of chymopapain A is different from the active centres of some other cysteine proteinases and that the Brønsted coefficient (beta nuc.) for the reactions of thiolate anions with 2,2'-dipyridyl disulphide may be decreased by reagent protonation.
    Author: Brocklehurst K, Baines BS, Mushiri MS.
    Journal: Biochem J; 1980 Jul 01; 189(1):189-29. PubMed ID: 7006597.
    Abstract:
    The active centres 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 disulphide and 5,5'-dithiobis-(2-nitrobenzoic acid) as thiol-specific reactivity probes. Whereas the first active-centre pKa values for chymopapain B and papaya peptidase A are less than 5, is as 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 approx. 6.5 with 2.2'-dipyridyl disulphide are essentially pH-independent in the pH range around the thiol pKa is delineated. The value of the Brønsted coefficient (beta nuc.) for the reactions of thiolate ions with the 2,2'-dipyridyl disulphide monocation appears to be smaller than its value for the corresponding reactions with the neutral disulphide.
    [Abstract] [Full Text] [Related] [New Search]