Impaired Conversion of Procollagen to Collagen by Fibroblasts and Bone Treated with Tunicamycin, an Inhibitor of Protein Glycosylation

Tunicamycin, an inhibitor of lipid carrier-dependent protein glycosylation, was used in studies of procollagen synthesis, secretion, and proteolytic modification by chick cranial bones in organ culture and by chick tendon fibroblasts in tissue culture. Tunicamycin inhibited the incorporation of D-[2-3H]mannose into procollagen by greater than 90% whereas general protein synthesis and collagen synthesis were decreased by only 10 to 20%. The procollagen synthesized in the presence of tunicamycin was secreted normally and its immunological characteristics, as detected by an antiserum to the intact protein, were unchanged. However, tunicamycin caused an accumulation of biosynthetic intermediates containing disulfide-bonded COOH-terminal extensions in both cell and bone culture. Cleavage of NH2-terminal extensions was not detectably impaired. These findings provide additional support for the involvement of more than one enzyme in the limited proteolytic conversion of procollagen to collagen.