Fat Metabolism in Higher Plants. VII. β-Oxidation of Fatty Acids by Peanut Mitochondria.

Abstract

The concept of /^-oxidation of fatty acids has been well documented in animal tissues. In 1943 Munoz and Leloir (12) prepared cell-free systems from rat liver that oxidized butyric acid to C02 and water. Kennedy and Lehninger (10) later showed that the site of fatty acid oxidation is the mitochondrion. Green and his co-workers (15) and Lynen (11) prepared soluble enzymes from acetone powders of liver mitochondria and demonstrated the individual steps involved in ?-oxidation of short and long chain saturated fatty acids. Until recently, little information was available to support the concept of ^-oxidation in plants. A large number of plant mitochondrial preparations have been tested for fatty acid oxidation with little if any success. However, support for the concept of the C2 fragment as the basic unit in fatty acid breakdown or synthesis in plants is now becoming apparent. Thus in 1953, Newcomb and Stumpf (13) showed that slices of cotyledons from both the developing and the germinating peanut readily oxidized acetate1-C14, butyrate-1-C14, and other radioactively labeled substrates to respiratory C1402, and that acetate was the most effective substrate of several tested for the synthesis of long chain saturated fatty acids. Gibble and Kurtz (5) have demonstrated that, in the utilization of acetate-1-C14 for the synthesis of long chain acids by immature flax fruit, the odd numbered carbon atoms of the fatty acid were highly radioactive whereas the even numbered carbon atoms were of low activity. In in vivo experiments with flax seedlings Fawcett et al (4) showed that when ?-phenoxyacids were supplied to the seedlings through their roots, only the acids with an even number of side chain m?thyl?ne groups gave rise to appreciable amounts of phenol, whereas those with an odd number of m?thyl?ne groups gave rise only to traces of phenol. The results were fully consistent with the idea that the side chains were degraded by ^-oxidation. Wain and Wightman (15) have extended this work to show that only those chloro derivatives of phenoxyaliphatic carboxylic acids which have side chains with an even number of carbon atoms (butyric, caproic, etc.) have herbicidal properties in plants like nettle, whereas those compounds with either propionic or valeric side chains are inert. These observations strongly suggest a ^-oxidation of the side chains of the phenoxy acids. This paper presents evidence that mitochondria obtained from cotyledons of germinating peanuts participate in the ?-oxidation of a large number of saturated fatty acids. In sharp contrast to liver mitochondria which require only ATP, Mg, a TCA cycle acid, and cytochrome c, the peanut mitochondria require ATP, CoA, DPN, TPN, Mn, a TCA cycle acid, and GSH for maximum activity.