Developmental Changes in Enzymes Involved in Dolichyl Phosphate Metabolism in Cultured Embryonic Rat Brain Cells

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The rates of synthesis of dolichol‐linked oligosaccharide intermediates and protein N ‐glycosylation increased substantially during a developmental period corresponding to glial differentiation in primary cultures of embryonic rat brain. In this study developmental changes in three enzymes involved in dolichyl phosphate (Dol‐P) metabolism have been examined by in vitro assays and correlated with the induction pattern for lipid intermediate synthesis and protein N ‐glycosylation. Dolichyl pyrophosphate (Dol‐P‐P) phosphatase activity was relatively low during the first 9 days in culture, but it increased significantly between days 9 and 25. Dol‐P‐P phosphatase did not change appreciably between days 22 and 30 in culture. A kinetic analysis of the developmental change in Dol‐P‐P phosphatase activity revealed that the V max increased 10‐fold between days 4 and 22, and there was also a significant change in the apparent K m for Dol‐P‐P. Dolichol kinase activity increased during the period (9–15 days) when there was a significant induction in oligosaccharide‐lipid synthesis and protein N ‐glycosylation, and then declined in parallel with lipid intermediate synthesis and protein N ‐glycosylation. Dol‐P phosphatase activity was present at relatively low levels for the first 9 days in culture, but it increased steadily between days 9 and 30. A kinetic comparison of the activity in membrane fractions from brain cells cultured for 9 and 25 days indicated that there was a 10‐fold increase in enzyme protein with unaltered affinity for Dol‐P. The results suggest that elevated dolichol kinase activity enhances the rate of lipid intermediate synthesis, and subsequent reciprocal changes in dolichol phosphorylation‐dephosphorylation are a regulatory factor in the deactivation of oligosaccharide‐lipid synthesis, and consequently of protein N ‐glycosylation, during the period following glial differentiation in primary cultures of embryonic rat brain cells.