Formation of alpha-1,2- and alpha-1,3-linked mannose disaccharides from mannosyl retinyl phosphate by rat liver membrane enzymes.

Mannosyl retinyl phosphate (MRP) was an active substrate for the transfer of mannose to methyl-alpha-D-mannose (CH3-alpha-man), p-nitrophenyl-alpha-D-mannose, and free mannose. The products formed during MRP incubation with CH3-alpha-man or with mannose were alpha-linked. The disaccharides formed by incubation of MRP with mannose were identified by paper chromatography and electrophoresis as mannose-alpha-1,2-mannose and mannose-alpha-1,3-mannose. Triton X-100 greatly inhibited mannose-alpha-1,3-mannose synthesis. In the absence of detergent, MnCl2, NiCl2, and ZnCl2 inhibited synthesis of both products. Formation of mannose-alpha-1,3-mannose was more sensitive to preincubation of the enzyme at 40 degrees C then was synthesis of mannose-alpha-1,2-mannose. No differences in membrane mannosyltransferase activity with MRP, compared to DMP, could be demonstrated.