Activation of prolyl hydroxylase in L-929 fibroblasts by ascorbic acid

The addition of ascorbate to the culture medium of early log-phase mouse fibroblasts (L-929 cells) resulted in a 5-fold increase of prolyl hydroxylase activity. Maximal activity was reached within 2 hr after addition of 5 muM ascorbate. The total amount of enzyme-related antigen did not change on treatment with ascorbate and the activation was shown to be independent of RNA and protein synthesis. The increase in activity caused by ascorbate is therefore due to the activation of a preformed precursor. Enzyme (molecular weight 260,000-300,000) and putative precursor (molecular weight 85,000-105,000) were separated by chromatography on DEAE-Sephadex. Treatment of intact cells with dithiothreitol resulted in an almost quantitative conversion of the enzyme to the smaller inactive protein. When these cells were treated with ascorbate or incubated overnight in fresh medium the enzyme reappeared and precursor concentrations decreased proportionately. Ascorbate may act by bringing about aggregation of enzymatically inactive subunits.