SEPARATION OF BRAIN DOLICHOL KINASE FROM ENDOGENOUS ACTIVATING FACTORS - EVIDENCE THAT PHOSPHOLIPID ENHANCES THE INTERACTION BETWEEN ENZYME AND DOLICHOL

Abstract: Porcine brain dolichol kinase activity is effectively solubilized by extracting salt‐washed microsomes with 1% 3‐[(3‐cholamidopropyl)dimethylammonio]‐1‐propanesulfonate (CHAPS). When the detergent‐solubilized activity is chromatographed on Sepharose CL‐6B, a low amount of dolichol kinase activity is recovered in the void volume, and a dolichol kinase activator (DKA) is eluted (Ve/Vo= 1.9‐2.2) with the bulk of the membrane phospholipids. Although only ˜20% of the activity applied to the Sepharose CL‐6B column is detected in the column fractions, virtually all of the original activity is restored when the Vo fraction is recombined with DKA. Endogenous DKA, isolated from brain microsomes, is heat‐stable, is extractable with CHCl3/CH3OH (2:1), and has the chemical and chromatographic properties of phosphatidylethanolamine (PE) and phosphatidylcholine (PC). Moreover, ˜50% of the stimulatory activity is lost when the PC present in the DKA fraction is degraded by purified phospholipase C from Clostridium perfringens. Also consistent with a phospholipid co‐factor requirement, the dolichol kinase activity recovered in the partially phospholipid‐depleted fraction (Vo) is markedly stimulated by various molecular species of exogenous purified PC or PE, but not by phosphatidylinositol, phosphatidic acid, phosphatidylserine, phosphatidylglycerol, or sphingomyelin. A comparison of defined molecular species shows that PCs containing oleoyl or linoleoyl groups in the 1 and 2 positions are the most stimulatory, suggesting that the fatty acyl moieties are involved in the enzyme‐phospholipid interaction. Kinetic analyses indicate that PC enhances the interaction between dolichol kinase and dolichol, the lipophilic substrate, but does not alter the apparent Km for CTP. These results demonstrate that brain dolichol kinase has a strict phospholipid co‐factor requirement, raising the possibility that the phospholipid composition of the rough endoplasmic reticulum plays a role in the regulation of dolichol phosphorylation in nervous tissue. Copyright © 1990, Wiley Blackwell. All rights reserved