vitamin-k-semiquinone-radical and calcium-phosphate--dibasic--anhydrous

Osteocalcin is an abundant Ca2+-binding protein indigenous to the organic matrix of bone, dentin, and possibly other mineralized tissues. This protein contains 47-50 amino acid residues (molecular weight 5,200-5,900) depending on the species. Osteocalcin is distinguished by its content of three gamma-carboxyglutamic (Gla) residues. The vitamin-K-dependent biosynthesis of osteocalcin occurs in bone, and the protein is not homologous to the Gla-containing regions of known vitamin-K-dependent blood coagulation proteins. The two major structural features of osteocalcin which appear to control its function include: the 'Gla helix', a compact Ca2+-dependent alpha-helical conformation, in which the three Gla residues are aligned to facilitate adsorption to hydroxyapatite, and the 'COOH-terminal beta-sheet' which exhibits chemoattractant activity toward mononuclear leukocytes, specifically monocytes, the putative precursors of osteoclasts. While the biological function of osteocalcin is unknown, it appears to be a highly specific osteoblastic marker produced during bone formation, and is rapidly becoming a clinically important diagnostic parameter of bone pathology. This article reviews recent advances in the understanding of osteocalcin.

Topics: Amino Acid Sequence; Animals; Bone Matrix; Calcium; Calcium Phosphates; Calcium-Binding Proteins; Humans; Osteocalcin; Protein Conformation; Vitamin D; Vitamin K

The precipitation of insoluble salts containing divalent metal ions is inhibited by Gla-containing proteins of various origin. In this paper we demonstrate that: Gla-residues are required for the inhibitory activity; the inhibition is effected by a protein which in vivo is bound to calcified tissue (osteocalcin) as well as by proteins occurring in blood plasma (factor X) and urine (the urinary Gla-protein); The inhibitor concentration required for 50% precipitation-inhibition varied slightly from one salt to the other, but no marked differences were observed between the effects of the various Gla-containing proteins used; Precipitation-inhibition occurred in all phosphates (Be, Ca, Mn and Zn) and in all calcium salts (phosphate, oxalate and carbonate) tested.

Topics: 1-Carboxyglutamic Acid; Calcium Phosphates; Calcium-Binding Proteins; Cations, Divalent; Chemical Precipitation; Factor X; Osteocalcin; Phosphates; Salts; Solubility; Vitamin K