Glyceryl Ether Monooxygenase [EC 1.14.16.5]: Stoichiometry and Inhibition

Abstract

Glyceryl ether monooxygenase is a microsomal enzyme which hydroxylates the α-carbon atom of the fatty side-chain of glyceryl ethers of long-chain fatty alcohols. The reaction requires oxygen and a tetrahydropterin cofactor. It is a mixed-function oxidase and by analogy with phenylalanine hydroxylase the reaction shown in Scheme ¹ was postulated.1 We investigated aspects of the stoichiometry of the oxygenase because two earlier reports were not entirely satisfactory. Tietz, Lindberg and Kennedy1 had shown that the amount of fatty aldehyde produced, in a non regenerating system, was 40-50% of tetrahydropterin oxidised and attributed this to the fact that the pterin was a DL mixture. This statement is incorrect in view of later work² and because we have found that the monooxygenase activity with the two separate enantiomers S(-) and R(+) 6-methyl-5,6,7,8-tetrahydropterin as cofactors is the same. The second report was by Kötting, Unger and Eibl³ who determined the stoichiometry of the reaction in a coupled reaction with DHPR and NADH, and showed that the amount of NADH oxidised after one minute was equivalent to the total amount of fatty aldehyde, alcohol and acid produced.³ Since the fatty aldehyde, alcohol and acid are produced by several reactions following enzymic hydroxylation of the ether substrate the conclusion was dubious.