Processing of NH sub(2)- and COOH-terminal peptides of rat osteocalcin by cathepsin B and cathepsin L

• Published in: Journal of bone and mineral metabolism 1998-01, Vol.16 (2), p.72-80
• Main Authors: Kobayashi, Y, Sakai, H, Ikeda, S, Kobayashi, K, Kato, Y, Mataki, S
• Format: Article
• Language: English
• ISSN: 0914-8779
• DOI: 10.1007/s007740050029

Rat osteocalcin was subjected to proteolysis by cathepsins B and L at acid pH in vitro. Short fragments of fewer than 8 amino acids were liberated from both the NH sub(2)- and COOH-termini of the molecule, but the midportion, composed of antiparallel alpha -helical domains, was resistant to proteolysis. Intact rat osteocalcin bound 10 Ca super(2+)/mol protein at pH 7.5 and the binding decreased to half that amount at pH 5.0, while the midportion fragment (Ala super(8)-Lys super(43)) bound 4-5 Ca super(2+)/mol protein at both pH 5.0 and 7.5. When COOH-terminal-truncated rat osteocalcin (Tyr super(1)-Lys super(43)) was prepared with lysyl-endopeptidase, it showed nearly the same Ca super(2+) binding as that of the intact molecule. Our results suggest that proteolytic processing of the terminal sequence of osteocalcin alters its intrinsic Ca super(2+)-binding capacity and that its NH sub(2)-terminal sequence is probably involved.