Hydrogen transfer by NADPH-dependent reductases in elongation of very-long-chain saturated and polyunsaturated fatty-acyl-CoA in swine cerebral microsomes.

The hydrogen transfer from NADPH was studied in the elongation of arachidoyl-CoA (20:0-CoA) and arachidonoyl-CoA (20:4-CoA) in swine cerebral microsomes. Previously, we showed that four deuterium atoms (2H) were transferred stereospecifically from (4S)-[4-2H1]NADPH in the elongation of 20:0-CoA to 24:0 (Yoshida, S., Takeshita, M. and Kawaguchi, A. (1984) Biochem. Biophys. Res. Commun. 124, 322-328), and that three deuterium atoms were transferred from 2H2O in the elongation of 20:4-CoA to 22:4. The deuteride transfer from (4S)-[4-2H1]NADPH was observed in the elongation of 20:4-CoA to 24:4, by the technique of mass fragmentography using the chemical ionization method, and, in this case, two 2H were transferred to 24:4. No deuteride was transferred from (4R)-[4-2H1]NADPH in the elongation of 20:0-CoA and 20:4-CoA. Moreover, the condensation product (3-keto-fatty-acyl-CoA) which was formed in the elongation without NADPH could be reduced by the addition of NADPH and sodium hydrosulfite, for the elongation of 16:0-CoA and 20:4-CoA, while the condensation product from 20:0-CoA could be reduced only by NADPH, but not by hydrosulfite. The hydrosulfite did not produce the final elongation products from 20:0-CoA, 16:0-CoA or 20:4-CoA. These results suggested that the hydride was transferred from NADPH stereospecifically only in the elongation of 20:0-CoA in the step of 3-ketoacyl-CoA reduction by the reductase which might be different from that for the elongation of 16:0-CoA and 20:4-CoA in which the proton exchange might occur via a water proton in the reduction of 3-ketoacyl-CoA. Accordingly, the hydride transfer might occur from NADPH in the step of 2,3-enoyl reduction in the elongation of 20:0-, 16:0- and 20:4-CoA.