Homology between a prolyl hydroxylase subunit and a tissue protein that crossreacts immunologically with the enzyme

A protein, enzymatically inactive but immunologically related to prolyl hydroxylase (prolyl-glycyl-peptide, 2-oxoglutarate:oxygen oxidoreductase; EC 1.14.11.2) (cross-reacting protein), has been purified to near homogeneity from skin of newborn rats. The purified protein has a molecular weight of 60,000 on gel filtration and sodium dodecyl sulfate gel electrophoresis, corresponding to that of the smaller of the two dissimilar subunits of the enzyme. The two subunits of prolyl hydroxylase differ markedly from one another in their amino acid compositions, but crossreating protein and the smaller subunit are very similar in composition. On antibody-affinity chromatography both subunits reacted with the antibody developed against the intact enzyme. Neither crossreacting protein nor the 60,000 molecular weight subunit was adsorbed onto concanavalin A, which adsorbed the intact enzyme as well as the larger subunit. It would appear that crossreacting protein is identical to one of the subunits of prolyl hydroxylase or metabolically related to it.