LIPIDS OF SUBCELLULAR PARTICLES FROM BOVINE HEART MUSCLE: I. FATTY ACIDS OF NEUTRAL LIPIDS

Abstract

The fatty acid composition of various lipid classes obtained from subcellular fractions of bovine heart muscle by column chromatography on silicic acid has been examined by gas-liquid chromatography on diethyleneglycol succinate and Apiezon L columns. The nuclear and cytoplasmic fractions together constituted the major lipid compartments of the myocardial cell, the cytoplasmic subcellular organelles accounting for only about 4% of the total lipid. Among the total fatty acids of each subcellular fraction, there was a remarkable constancy in the relative amounts of monoethenoid fatty acids (about 23%). More than 90% of the total fatty acids had chain lengths between C18and C20. Approximately 3–4% of longer chain length fatty acids were present in the mitochondrial and cytoplasmic fractions. There was a predominance of monoenes (36%) and long chain fatty acids (> C20) in the cholesteryl esters associated with the "microsomal" preparation. Although the monoethenoid fatty acids of triglycerides were subject to considerable variation, the nuclear and cytoplasmic compartments consistently showed about 40% of this class of fatty acid. In sharp contrast to all other neutral lipid classes, polyethenoid fatty acids constituted a significant proportion of the total free fatty acids in all subcellular organelles. The heavy mitochondrial and cytoplasmic fractions showed relatively higher concentrations of polyethenoid free fatty acids. In view of the fact that free fatty acids constituted the main source of energy from fats for the myocardium, the hypothesis has been advanced that heart muscle mitochondria preferentially extract the readily oxidizable free polyunsaturated fatty acids from the cytoplasmic environment to fulfill the energy demands of the aerobic cell.