Bone cell phosphotyrosine phosphatase: characterization and regulation by calcitropic hormones.

Isolated bone cells in culture contain an enzyme capable of hydrolyzing the phosphate ester of phosphotyrosine. This enzyme, which we have termed phosphotyrosine phosphatase, has not previously been reported in bone. Some of its characteristics include: 1) maximum activity near physiological pH, 2) a Km for substrate of 52 microM, 3) marked inhibition by the phosphate analog vanadate ion, 4) activity correlation with bone cell alkaline phosphatase, and 5) regulation by bone target hormones. Data obtained with vanadate ion support the contention that this enzyme may play a role in the regulation of bone cell growth.