Abstract
Dolichyl D-[14C]mannosyl phosphate formed in calf pancreas microsomes was compared to dolichyl alpha-D-[14C]mannopyranosyl phosphate, a chemical synthesis of which is described. Jack bean alpha-mannosidase, which converted citronellyl alpha-D-mannopyranosyl phosphate, but not its beta anomer, to citronellyl phosphate and D-mannose, was effective in releasing D-[14C]mannose from dolichyl alpha-D-[14C]manopyranosyl phosphate in the presence of detergent. In contrast, alpha-mannosidase did not cause any significant release from the pancreatic dolichyl D-[14C]mannosyl phosphate. Alkali treatment (0.1 M NaOH in propanol at 65 and 90 degrees) degraded both dolichyl D-[14C]mannosyl phosphates with the formation of water-soluble 14C-labeled products. The pattern of 14C-labeled breakdown products formed from the synthetic dolichyl alpha-D-[14C]mannopyranosyl phosphate differed from that obtained from the pancreatic dolichyl D-[14C]mannosyl phosphate. Dolichyl alpha-D-[14C]mannopyranosyl phosphate yielded several 14C-labeled products, including a trace of D-[14C]mannosyl phosphate, and an acidic fraction which appeared to result from degradation of D-[14C]mannose. The pancreatic dolichyl D-[14C]mannosyl phosphate gave various products, depending on the temperature of the reaction: at 90 degrees, 20 to 30% of the radioactivity was found in D-[14C]mannosyl phosphate and the rest in acidic breakdown products; at 65 degrees, about two-thirds of the radioactivity was recovered in a compound which behaved as D-MANNOSE 2-PHOSPHATE, A Product characteristic of a beta-linked D-mannosyl residue. It is concluded that the pancreatic compound is dolichyl beta-D-[14C]mannosyl phosphate.
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