Phytanic acid alpha-oxidation in rat liver. Requirement of cytosolic factor

The alpha-oxidation of [1-14C]phytanic acid of high specific activity was studied in postnuclear and various subcellular fractions from rat liver. alpha-Oxidation in the postnuclear fraction required ATP, Mg2+, nicotinamide, and molecular oxygen for activity. alpha-Oxidation was inhibited by iron-specific chelating agents and respiratory chain inhibitors. Partial inhibition by carbon monoxide indicated a possible involvement of cytochrome P-450. However, phenobarbital-treated rat liver postnuclear fraction did not stimulate phytanic acid alpha-oxidation above that of control. Subcellular fractionation indicated that in addition to the mitochondrial fraction, cytosol was required for activity. The cytosolic factor appeared to be dialyzable; it was inactivated by heat treatment, but not affected by trypsin digestion. NAD, CoA, ascorbic acid, and catalase did not replace cytosolic activity nor did the recently characterized heat-stable factors in brain hydroxylation, namely, adenosine nucleotides and glutamate.