Metabolism of osteocalcin

After intravenous injection, labeled bovine osteocalcin was rapidly removed from rat plasma and taken up mainly by kidney, liver, and bone. The rate of disappearance was slowed by nephrectomy but not as much by ureteric ligation, suggesting renal destruction of osteocalcin rather than renal excretion. Both liver and kidney tissue rapidly degraded osteocalcin, both in vivo and in vitro. The enzyme activity was found in microsomal, mitochondrial, and supernatant fractions. EDTA was the most potent inhibitor, suggesting that metalloenzymes are involved. Comparison of three methods of analysis--trichloroacetic acid precipitation, gel filtration on Sephadex G-50, and SDS polyacrylamide gel electrophoresis--showed that the last gave a much faster rate of degradation of osteocalcin and suggests that osteocalcin and/or fragments bind to larger proteins in the tissue homogenates.