Cell density-dependent increase in prolyl hydroxylase activity in cultured L-929 cells requires de novo protein synthesis.

Prolyl hydroxylase activity in cultured L-929 cells was found to increase when cells grew from log phase to stationary phase and when cells were harvested at the mid-log phase and replated at higher cell densities. Cycloheximide and actinomycin D inhibited the cell density-dependent increase in prolyl hydroxylase activity indicating that the increase in prolyl hydroxylase activity required de novo synthesis of protein and RNA. Prolyl hydroxylase was purified from cultured L-929 cells and antibodies against the protein were raised in rabbits. The antibodies were used to demonstrate that L-929 cells contained two forms of prolyl hydroxylase: an enzymatically active, tetrameric form consisting of two alpha and two beta polypeptide chains and an enzymatically inactive form containing immunologically cross-reacting protein. The polypeptide chains alpha, beta and cross-reacting protein were obtained by immunoadsorption. Peptide map analysis indicated that cross-reacting protein was similar if not identical to beta in primary structure, and alpha was different from both beta and cross-reacting protein. The results suggested that the prolyl hydroxylase levels in cells or tissues may be regulated by new protein and/or RNA synthesis.