Biosynthesis of the vacuolar yeast glycoprotein carboxypeptidase Y. Conversion of precursor into the enzyme

Hasilik, A.; Tanner, W.

European Journal of Biochemistry 85(2): 599-608

1978


ISSN/ISBN: 0014-2956
PMID: 348476
DOI: 10.1111/j.1432-1033.1978.tb12275.x
Accession: 068526748

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Abstract
The vacuolar glycoprotein carboxypeptidase Y is redistributed from the sedimenting fraction into the soluble one as the precursor is converted to the enzyme. The precursor protein is not identical with the enzyme-inhibitor complex described previously by Hayashi et al. The incorporation of radioactive mannose into the precursor indicates that the glycosylation takes place before or immediately after the completion of the syntheses of the polypeptide chain. The precursor is converted by trypsin in vitro to a protein identical in size to carboxypeptidase Y. The extra piece released by trypsin probably contains 4 phenylalanine and at least 10 leucine residues. Of 3 yeast proteinases tested in vitro only the proteinase B catalyzed conversion of the precursor to a protein identical in size to carboxypeptidase Y. The conversion in vivo, which presumably is an example of intracellular-limited proteolysis, proceeds with a half-life of about 6 min. It is assumed that the precursor is an inactive pro-enzyme, procarboxypeptidase Y, rather than a pre-enzyme and that, as inactive hydrolase, it exists only during the time required for the intracellular transport to the vacuole, where the pro-enzyme is activated.