Phosphopeptides and γ-carboxyglutamic acid-containing peptides in calcified turkey tendon: Their absence in uncalcified tendon

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Abstract
Uncalcified samples of turkey tendon obtained prior to calcification, and other samples from areas of tendon that never calcify, contain little or no 0-phosphoserine [Ser(P)], 0-phosphothreonine [Thr(P)] and γ-carboxyglutamic acid (Gla). Significant amounts of all three of these Ca2+-binding amino acids, which are found in EDTA-extractable, non-collagenous proteins, are detected coincident with the onset of mineralization of a tendon and increase in concentration as mineralization proceeds.