Studies on Microsomal Phospholipids That Inhibit Gulonolactone Oxidase

Fractions of rat liver microsomal phospholipid that inhibit gulonolactone oxidase are described. The inhibition was shown to be complete and occurs rapidly after the reaction has proceeded at the control rate for 20 to 30 min. It could be totally reversed by the addition of tocopherol, Mn++, Co++, or ethylenediaminetetraacetate. The inhibitory activity of the phospholipid was lost by enzymic cleavage of the β-acyl fatty acid moiety or by hydrolysis of the bases associated with the phosphatidyl group. Diglycerides derived from the lipid retained significant inhibitory properties. The inhibition is apparently accompanied by alterations of unsaturated fatty acids resulting in formation of chromogenic substances that react with thiobarbituric acid. When the degree of unsaturation of the inhibitor phospholipid is reduced, both the inhibitory properties and formation of chromogens are proportionally decreased.