Fat metabolism in higher plants. Beta-hydroxylation of fatty acids by a soluble preparation from maturing avocado mesocarp.

1. An avocado supernatant fraction converted fatty acids of medium chain length (C(8)-C(12)) into a polar product. 2. The product was identified as the beta-hydroxy derivative of the substrate by g.l.c. and t.l.c. analysis. 3. For hydroxylation of the fatty acids, CoA, ATP and molecular oxygen were required. Acyl carrier protein gave some stimulation. The reaction took place with oxygen alone if acyl-CoA was the substrate. 4. Hydroxylation was maximal with decanoic acid but dodecanoic acid and octanoic acid were also very active. Acids of shorter or longer chain lengths were not hydroxylated. 5. NAD(+) concentration caused complete inhibition at 0.5mm and may be an important control mechanism for the reaction in vivo. 6. The reaction was inhibited by iodoacetamide and by bipyridyl and carbon monoxide, indicating involvement of thiol and heavy metal groups.