Studies on enzymes of collagen biosynthesis and the synthesis of hydroxyproline in macrophages and mast cells

The activities of four intracellular enzymes of collagen biosynthesis were assayed in freshly isolated rat peritoneal macrophages and mast cells and compared with the same enzymes in freshly isolated chick-embryo tendon cells. The macrophages were found to contain activities of all four enzymes, those of prolyl and lysyl hydroxylase being 7 and 12% respectively of those in the tendon cells when expressed per cell or 3 and 4% when expressed per unit of soluble cell protein. The corresponding values for hydroxylysyl galactosyltransferase and galactosylhydroxylysyl glucosyltransferase activities were about 82 and 68% or 32 and 24% respectively. When the macrophages were incubated in suspension with (14)C]proline, they synthesized a small but significant amount of non-diffusible hydroxy(14)C]proline. The synthesis per cell was only about 0.1% of that formed by the tendon cells, and its distribution between the cells and the medium also differed from that in the tendon cells. The hydroxy(14)C]proline synthesized by the macrophages may be present in the Clq subcomponent of the complement, but its amount was too small to allow any characterization of the protein. All four enzyme activities, and in particular the two hydroxylysyl glycosyltransferase activities, seem to be present in macrophages in a large excess compared with the very low rate of synthesis of hydroxy-proline-containing polypeptide chains. The mast cell extract was found to inhibit all four enzyme activities, but even when corrected for this inhibition, prolyl and lysyl hydroxylase activities in the mast cells were less than 0.08% and the two hydroxylysyl glycosyltransferase activities less than 1% of those in the tendon cells. The intracellular enzyme pattern of collagen biosynthesis in the mast cells is thus completely or virtually completely repressed.