The citric acid or tricarboxylic acid cycle is a central element of higher-plant carbon metabolism which provides, among other things, electrons for oxidative phosphorylation in the inner mitochondrial membrane, intermediates for aminoacid biosynthesis, and oxaloacetate for gluconeogenesis from succinate derived from fatty acids via the glyoxylate cycle in glyoxysomes. The tricarboxylic acid cycle is a typical mitochondrial pathway and is widespread among a-proteobacteria, the group of eubacteria as de®ned under rRNA systematics from which mitochondria arose. .
