The influence of dietary calcium deficiency and parathyroidectomy on bone collagen structure

Abstract

Bone collagen synthesized in chicks fed a calcium-deficient diet had the same chain composition as that normally synthesized, but differed in that in both α1- and α2-chains there was an increased conversion of lysine to hydroxylysine, of about 50–70%, equivalent approximately to an extra five residues of hydroxylysine in the α1- and an extra six to seven residues in the α2-chain. This effect was not due to the hyperparathyroidism accompanying the calcium deficiency since increased hydroxylation was also observed when calcium levels were reduced following parathyroidectomy. It is suggested the effect may be directly attributable to reduced calcium levels and that the increased hydroxylation of bone collagen lysine occurring in rickets may also be attributable to the reduced level of calcium existing in vitamin D deficiency. Examination of skin collagen indicated a slight increase in hydroxylation, equivalent only to an extra one to two residues of hydroxylysine, in the α1-chains. A similar slight increase in the α2-chains was not unequivocably demonstrated. The results suggest lysine hydroxylation in bone collagen to be much the more sensitive to changes in calcium level and the possible significance of this, particularly in relation to mineralization, is considered.