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Further studies on subunit III of bovine procarboxypeptidase A
Author(s) -
Wicker Catherine,
Puigserver Antoine
Publication year - 1981
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(81)81067-8
Subject(s) - citation , art , protein subunit , humanities , chemistry , microbiology and biotechnology , philosophy , library science , biology , computer science , biochemistry , gene
The activation of pancreatic zymogens results from the tryptic cleavage of the first basic bond in the N-terminal part of the molecules [ 11. As indicated by crystallographic data [2,3], the major event induced by this cleavage is the appearance at the newly formed N-terminus of the chain of a positively charged hydrophobic residue (Ile 16 in bovine chymotrypsinogen A) which moves into the interior of the molecule and forms an ion pair with the buried carboxylate of Asp 194. The concomitant repositioning of other residues, has been proposed to improve the structure of the primary substrate binding site and that of the oxyanion hole [4]. However, the charge relay system between Asp 102, His 57 and Ser 195 which plays a key role in catalysis is largely if not fully developed in the zymogens. The resulting latent active sites are able to react at a measurable rate with titrants and substrates ]51. Bovine procarboxypeptidase A is composed of 2 or 3 subunits [6,7] which can be dissociated under nondenaturing conditions after dimethylmaleylation of the complex [8]. Subunit I is the immediate precursor of carboxypeptidase A whereas subunit 11 is a chymotrypsinogen of the C type [9]. In contrast, no activity has ever been found in subunit III prior to or following tryptic treatment. This subunit has been assumed to be a new type of a non-activatable zymogen for the following 2 reasons: