Abstract
Fatty acids can be synthesized in mitochondrial membranes of rat liver either by elongation or by synthesis de novo. The outer membranes incorporate greater amounts of substrate into fatty acids than do the inner membranes. Outer membranes synthesize 6- and 8-carbon fatty acids completely de novo, while smaller amounts of 10-carbon acids are produced by the mechanism de novo. The reactions de novo utilize acetyl coenzyme A more effectively than malonyl coenzyme A, and synthesis de novo occurs in the absence of exogenous ATP. Elongation, which produces fatty acids 14 carbon atoms long and longer, depends on added ATP, and acetyl-CoA and malonyl-CoA are incorporated about equally. Synthesis de novo of shorter chain fatty acids by outer membranes continues in the presence of ATP and the concomitant elongation reactions. Inner membranes synthesize only longer fatty acids by elongation. If synthesis de novo of fatty acids occurs in the inner membranes, these acids might be removed by oxidation. The ATP concentrations in these experiments were compared with the levels of ATP produced by actively respiring liver mitochondria. During metabolically adverse conditions within the cell, the capacity for manufacturing fatty acids by elongation may fluctuate with the ATP levels whereas synthesis de novo continues.
Highlights
The outer membranes incorporate greater amounts of substrate into fatty acids than do the inner membranes
Characterization of Mitochondrial Membranes-Electron micrographs showed that the outer membranes were of the same general appearance and size as the vesicular structures pictured by Parsons et al [21]
With the isolation procedure used, there was no visible contamination of the outer by the inner membrane, and only a very few (
Summary
Fatty acid biosynthesis occurs by different mechanisms in different parts of the cell. Complete synthesis de no00 in the cytoplasm utilizes malonyl coenzyme A formed from acetyl COenzyme A (l-3). Malonyl-CoA is the substrate for fatty acid elongation by the microsomes [4, 5]. Mitochondria carry out elongation [2] with either acetyl coenzyme A or malonyl. Research Center, supported in part by Grant FR-00163 of the National Institutes of Health. Grant HE-09744 from the National Institutes of Health, United. States Public Health Service to Dr 0.
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