Dependence of an alkyl glycol-ether monooxygenase activity upon tetrahydropterins

Abstract

Glyceryl-ether monooxygenase (1-alkyl-sn-glycerol,tetrahydropteridine:oxygen oxidoreductase, EC 1.14.16.5) catalyzes the oxidative cleavage of 1-O-alkyl glycerol or glycol derivatives to a long-chain aldehyde and the glycerol or glycol derivative. The specificity for tetrahydropterins of a similar, perhaps identical, enzyme that cleaves O-hexadecyl ethylene glycol in rat liver microsomes was examined with the use of an assay based on [1-3H]ethylene glycol formation from 2-hexadecyloxy[1-3H]ethan-1-ol. Several tetrahydropterin derivatives are effective electron donors for this reaction, and 2,4,5-triamino-6-hydroxypyrimidine is somewhat effective, but NADH, NADPH, ascorbate, reduced dichlorophenolindophenol and glutathione are inactive. Tetrahydropterin derivatives differ from each other in apparent Km and apparent Vmax. The order of increasing apparent Km values is tetrahydropterin [approximate] 6-methyltetrahydropterine [approximate] tetrahydrobiopterin Vmax values is tetrahydrofolate [approximate] tetrahydropterin P-450-dependent hydroxylases, this alkyl glycol-ether monooxogenase is not inhibited by carbon monoxide. 1-O-hexadecyl-rac-glycerol (chimyl alcohol) competitively inhibits the oxidation of the glycol ether indicating that the same enzyme probably catalyzes the oxidation of both O-alkyl glycol and 1-O-alkyl glycerol.