PEROXISOMAL METABOLISM OF ADRENIC ACID - NO DELTA-4 DESATURASE DETECTED IN RAT-LIVER PEROXISOMES

The existence of a peroxisomal Delta 4 desaturation of 22:4n-6 and 22: 5n-3 to yield, respectively, 22:5n-6 and 22:6n-3 has been questioned. An alternative pathway has been formulated to include microsomal chain elongation and Delta 6 desaturation and peroxisomal chain shortening. We incubated [1-C-14]adrenic acid (22:4n-6) in a system for desaturat ion (i.e., in the presence of NADH) with purified rat liver peroxisome s. The fatty acids were separated as methyl derivatives by high-perfor mance liquid chromatography. Four ultraviolet-absorbing product peaks appeared, three of which contained radioactivity, which we investigate d as methyl, trimethylsilyl, and oxazoline derivatives on gas chromato graphy-mass spectrometry. In addition to adrenic and arachidonic acids , the product peaks were trans-enoyl, hydroxy, and keto derivatives of adrenic acid: the three first steps of beta-oxidation cycle. This ind icated that the NAD-dependent dehydrogenase step in the peroxisomal be ta-oxidation cycle of adrenic acid was inhibited due to a high concent ration of added NADH. Incubation in the presence of NAD instead of NAD H reduced radioactivity in the peaks that corresponded to intermediate s, while radioactivity in the acid-soluble fraction increased consider ably, consistent with a complete beta-oxidation cycle of adrenic to ar achidonic acid. There were no indications of Delta 4 desaturation in p urified peroxisomes incubated in a standard desaturation system. Inste ad, adrenic acid as substrate underwent beta-oxidation.