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J Biol Chem. 1993 Jul 5;268(19):14294-300.

Phosphorylation of connexin-32 by protein kinase C prevents its proteolysis by mu-calpain and m-calpain.

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  • 1Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Cientificas, Madrid, Spain.

Abstract

Isolated connexin-32s from rat and mouse liver are proteolyzed in vitro by the intracellular Ca(2+)-dependent neutral proteases, mu-calpain and m-calpain, producing a major fragment of 26 kDa. Connexin-26 is not proteolyzed by calpain. Calpain cleaves connexin-32 at its C-terminal end as shown by 125I-calmodulin binding experiments. Connexin-32, but not connexin-26, is phosphorylated by both protein kinase A and protein kinase C in serine residues and the sites of phosphorylation by both kinases remain in the major 26-kDa fragment resulting from calpain proteolysis. Phosphorylation of connexin-32 by protein kinase C, but not by protein kinase A, prevents the proteolytic attack of mu-calpain and m-calpain. Phosphorylation of connexin-32 by protein kinase A and protein kinase C does not prevent its proteolysis by papain, alpha-chymotrypsin, proteinase K, and trypsin.

PMID:
8390988
[PubMed - indexed for MEDLINE]
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