A collagen:glucosyltransferase at the surface of malignant fibroblasts

3T12 fibroblasts possess glucosyltransferases that catalyze the transfer of glucose from UDP-Glucose to galactosylhydroxylysyl residues on collagenous acceptors. The presence of the enzyme activity at the cell surface is indicated by the following findings: a) suspensions of intact cells, as well as intact cell monolayers, glucosylate gelatinized collagen b) glucose transfer is not due to UDP-Glucose hydrolysis and subsequent intracellular utilization of the free glucose c) experiments using cell suspensions with known proportions of broken cells indicate that the glucosyltransferase activity is attributable to intact cells and not to contamination by intracellular enzymes from broken cells. The Km value for UDP-Glucose is about 20 microM. The enzyme has a pronounced requirement for manganese, and shows highest activity between 2 and 10 mM. The optimal Mn2+ concentration for the intracellular gelatin:glucosyltransferase activity is more restricted (5 to 10 mM). Glucosyltransferase activity is strongly inhibited by diamide and N-ethylmaleimide (5 mM), suggesting that intact sulfhydryl residues present in the enzyme are essential.