SYNTHESIS OF HUMAN OSTEOCALCINS - GAMMA-CARBOXYGLUTAMIC ACID AT POSITION-17 IS ESSENTIAL FOR A CALCIUM-DEPENDENT CONFORMATIONAL TRANSITION

Human osteocalcins having two (positions 21 and 24) or three (position s 17, 21 and 24) gamma-carboxyglutamic acids (Gla) were synthesized in solution employing both the Boc strategy and the HF procedure for the final deprotection. During synthesis, the gamma,gamma-dicarboxyl, fun ctional groups of the Gla residues were protected by the cyclohexyl gr oup. The identity of the synthetic peptides was confirmed by amino aci d analysis, mass spectrometric measurement and peptide mapping. Circul ar dichroism measurement showed that the conformation of osteocalcin c ontaining three Gla residues dramatically changed on addition of calci um ions, whereas the peptide containing glutamic acid at position 17 d id not. These findings clearly show that the Gla residue at position 1 7 is essential for a calcium-dependent conformational transition of os teocalcin.