Immunological evidence for an inactive precursor of collagen proline hydroxylase in cultured fibroblasts.

A specific antibody to rat collagen proline hydroxylase has been used to measure the amount of "enzyme" protein in cultured mouse fibroblasts (L-929 cells) during normal growth, and under other conditions that cause an increase in enzyme activity. Collagen proline hydroxylase activity per mg of cell protein increased 24-fold as the cells progressed through the logarithmic to the stationary phase of growth, while the cellular concentration of immunologically reactive protein changed only slightly. Similar results were obtained with cells in early log phase in which enzyme activity was stimulated severalfold by cell concentration or lactate treatment without a corresponding change in cellular antigen. It has also been shown that the enzymatically inactive antigen in these fibroblasts competes effectively for antibody-binding sites with partially purified enzyme. It is concluded that early-log-phase fibroblasts contain an inactive form of collagen proline hydroxylase which may be a precursor of the functional enzyme.