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Dolichyl-phosphate phosphatase and dolichyl-diphosphate phosphatase activities of a liver-cell microsomal preparation were solubilized by treatment with Triton X-100. The I00000 x g supernatant was then passed through a column of Sepharose-4B -concanavalin A. Both enzyme activities were found in the percolate. This treatment eliminated inhibition by ATP and glucose 6-phosphate in both phosphatase activities. In each case the activities were inhibited by higher concentrations of enzyme preparation due to the presence of phospholipids. The inhibitory effects of either phosphatidylcholine or phosphatidylethanolamine were due to competition for detergent. On the other hand, the effect produced by phosphatidic acid appeared to be different, since it did not change the optimal concentration of Triton X-100 for the two enzymes. Dolichyl-phosphate phosphatase was strongly inhibited by both Pi and PPi, whereas dolichyl-diphosphate phosphatase was only slightly inhibited by Pi and not at all by PPi. Dolichyl-diphosphate phosphatase was more inhibited by divalent cations than dolichyl-phosphate phosphatase. The apparent K,,, of dolichyl-phosphate phosphatase for dolichyl phosphate was 0.15 mM. Dolichol also inhibited dolichyl-phosphate phosphatase, but it produced a stronger inhibition on dolichyl-diphosphate phosphatase. The inhibitory effect of dolichol was not entirely due to detergent competition.The enzymatic system involved in the biosynthesis of asparagine-linked glycoproteins is located in the endoplasmic reticulum. In this biosynthetic process the formation of the peptide linkage precedes the formation of the covalent bond between oligosaccharide and amino acid. During the last decade experimental evidence has shown that, at least in the case of asparagine-type glycoproteins, the oligosaccharide moiety is built up linked to dolichol diphosphate. The Dol-P-P moiety is released when to oligosaccharide moiety is transferred to the peptide chain [1,2]. Since the biosynthesis of the oligosaccharide lipid is initiated with dolichyl monophosphate as an acceptor of the first glycosyl groups, it seems reasonable to assume the existence of a conversion step from Dol-P-P to Dol-P, which would complete the cycle.Some suggestions [3] and further experimental evidence [4-71 indicate that an increased concentration of dolichyl phosphate would in turn increase the rate of glycoprotein synthesis. The Dol-P concentration would be determined by the activity of the following three enzymes.a) The enzyme that forms Dol-P from dolichol, dolichol phosphokinase [8-111, which catalyzes the reaction Dolichol + CTP -+ Dol-P + CDP .b) The enzyme that forms Dol-P by a cleavage of the pyrophosphate bond of Dol-P-P, Dol-P-P phosphatase [I2 -141. The reaction is Dol-P-P + Dol-P + Pi.c) The enzyme that lowers Dol-P concentration through a transformation of the latter into dolichol, Dol-P phosphatase [12,13,15,16].Abbreviations. Dol-P-P, dolichyl diphosphate; Dol-P, dolichyl phosphate.In the studies reported below we have focused on the characteri...

Phosphoglucomutase for β‐glucose 1‐phosphate, an enzyme present in cell‐free extracts of Euglena gracilis var. bacillaris, catalyzes the reversible conversion of β‐glucose 1‐phosphate to glucose 6‐phosphate. It was purified 460‐fold by treatment with protamine sulphate, gel filtration in Sephadex G‐100 and chromatography on a DEAE‐cellulose column. The optimum pH of the reaction was 7.0 and the equilibrium constant β‐glucose 1‐phosphate/glucose 6‐phosphate was 0.035. The enzyme has an absolute requirement for β‐glucose 1,6‐bisphosphate as well as a bivalent cation such as Mg2+, Co2+ or Mn2+. Measurements in Sephadex G‐100 gave an apparent molecular weight of about 27000. This enzyme together with a trehalose phosphorylase found in the same Euglena extracts would constitute a new catabolic pathway for trehalose. The functions of α‐ and β‐glucose 1,6‐bisphosphate as regulation factors in the energy furnisher system in Euglenais discussed.

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