[The action of calcium on the step of collagen metabolism, catalyzed by procollagen-proline hydroxylase].

Calcium effects on procollagen-proline-hydroxylase activity of chick embryo tibias was studied. Serial preincubation of the natural substrate, the enzymatic preparation or the mixture of both with and without calcium showed that calcium decreased procollagen-prolin-hydroxylase affinity for procollagen, decreased the maximum velocity of the reaction by binding to the substrate and by increasing the thermosensitivity of the enzyme -- substrate complex. Calcium could also increase the maximum velocity by dissociation of an enzyme -- inhibitor ligand complex. The resulting decrease of the overall reaction rate has been discussed in the context of the relationship between collagen metabolism and calcium fixation during calcification.