Tyrosylprotein kinase and phosphatase activities in membrane vesicles from normal and Rous sarcoma virus-transformed rat cells.

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Abstract
Membrane vesicles, isolated from normal and Rous sarcoma virus-transformed rat cells, have an associated cAMP independent kinase that phosphorylates a MW 37,000 protein in vesicles from normal cells and proteins of MW 37,000, 50,000 and 67,000 in vesicles from transformed cells. Proteins in vesicles from normal and transformed cells contain 9% and 77%, respectively, of their labeled phospho amino acids as phosphotyrosine. Thus, isolation of vesicles and subsequent incubation with [.gamma.-32P]ATP enriches the proportion of labeled phosphotyrosine in proteins (relative to other phospho amino acids) by 2 orders of magnitude over that found in intact cells. The in vitro phosphorylation of each of these proteins is enhanced in the presence of 10 .mu.M Zn2+, a phosphotyrosylprotein phosphatase inhibitor. Membrane vesicles may be a valuable system for examination of transformation-specific phosphorylation of proteins.