Dolichyl phosphate-mannosyltransferase and dolichyl phosphate-N-acetylglucosaminyltransferase activities in liver preparations from normal controls and patients with cystic fibrosis and diabetes mellitus.

Optimal assay conditions have been determined in human liver preparations for the catalytic transfer of mannose and N-acetylglucosamine from GDP-mannose and UDP-N-acetylglucosamine, respectively, to dolichyl phosphate. Both enzymatic reactions have an absolute requirement for divalent cation (5 mmol/l Mn2+ optimal), detergent (Triton X-100 or Nonidet P-40) and dolichyl phosphate (as acceptor substrate) and both reactions have optimal activity at a pH value of 7.8. Preliminary characterization of the glycolipid products for both enzymatic reactions indicates that phosphorylated dolichol is the major acceptor substrate for radiolabeled mannose and N-acetylglucosamine. The activity levels and specific activities of dolichyl phosphate-mannosyltransferase are comparable in liver homogenates from normal controls and patients with cystic fibrosis and diabetes mellitus. The activity levels and specific activities of dolichyl phosphate-N-acetylglucosaminyltransferase are comparable in liver homogenates from normal controls and patients with cystic fibrosis and diabetes mellitus but considerably lower than the activity levels of dolichyl phosphate-mannosyltransferase. It appears that two of the initial steps of the lipid-mediated glycosylation pathway are normal in livers from patients with cystic fibrosis and diabetes mellitus.