Glyceryl-ether monooxygenase [EC 1.14.16.5]. Part 9. Stereospecificity of the oxygenase reaction

(2RS,1′R)-[1′-3H1 ]- and (2RS, 1′S)-[1′-3H1]-Hexade cyloxypropane-1,2-diols (chimyl alcohols) have been prepared and their stereochemistry has been confirmed by synthesizing the [2H1]-analogues using similar procedures. When they were used as substrates for glyceryl-ether monooxygenase from rat liver in the presence of oxygen and (RS)-6-methyl-5,6,7,8-tetrahydropterin as co-factor, the 1′S-isomer released 37% of its tritium into the aqueous buffer after 20 mins, whereas the 1′R-isomer released only 6.5% showing that the reaction was stereospecific for the pro-HS hydrogen atom of the glyceryl ether substrate. This was in agreement with the kinetic parameters of unlabelled-(2RS)-3-, (2RS, 1′R)-3-[1′-2H1]-, (2RS, 1′S)-3-[1′-2H1]- and (2RS)-3-[1′,1′-2H2]- hexadecyloxypropane-1,2-diols where the apparent Km values were about the same (49.4, 53.7, 49.3 and 54.0 µM respectively) but the apparent maximum velocities (Vmax in nmol min-1 mg-1 protein) of the first two substrates (37.5 and 37.5) were faster than for the latter two substrates (22.5 and 23.6), consistent with the pro-HS hydrogen atom being replaced by the hydroxy group and a primary deuterium isotope effect of ≈1.6.