STUDIES ON ENZYMES OF COLLAGEN BIOSYNTHESIS AND THE SYNTHESIS OF HYDROXYPROLINE IN MACROPHAGES AND MAST-CELLS

The activities of 4 intracellular enzymes of collagen biosynthesis were assayed in freshly isolated rat peritoneal macrophages and mast cells and were compared with the same enzymes in freshly isolated chick-embryo tendon cells. The macrophages contained activities of all 4 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 [14C]proline, they synthesized a small but significant amount of nondiffusible hydroxy[14C]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[14C]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 4 enzyme activities, and in particular the 2 hydroxylysyl glycosyltransferase activities, seem to be present in macrophages in a large excess compared with the very low rate of synthesis of hydroxyproline-containing polypeptide chains. The mast cell extract inhibited all 4 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 2 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.