Decarboxylated bone Gla-protein as a substrate for hepatic vitamin K-dependent carboxylase

Bovine bone Gla-protein (B.G.P.) was prepared and decarboxylated into descarboxy-B.G.P. (d-B.G.P.). The latter was purified and identified as decarboxylated osteocalcin. Both crude and purified d-B.G.P. are good substrates for vitamin K-dependent carboxylase. Because the Km of this enzyme for d-B.G.P. is low, the latter is a better substrate than the frequently used pentapeptide FLEEL or exogenous protein substrates such as descarboxyprothrombin.