Long chain fatty acid activation, entry into mitochondria and metabolism via fatty acid oxidation.

Entry of long chain fatty acids into mitochondria requires activation by acyl-CoA synthetase enzymes which catalyze the transfer of CoA from CoA-SH to form fatty acyl-CoA. Activated fatty acids enter mitochondria via enzymatic transfer of CoA for carnitine which is catalyzed by carnitine palmitoyl transferase I (CPTI). Fatty acyl-carnitine enters the mitochondrial matrix via carnitine acylcarnitine translocase where carnitine palmitoyl transferase II (CPTII) replaces carnitine with CoA. This is known as the carnitine shuttle. Fatty acyl-CoA then enters the fatty acid oxidation spiral which has 4 steps catalyzed by 1) fatty acyl CoA dehydrogenase, 2) enoyl CoA hydratase, 3) hydroxyacyl CoA dehydrogenase and 4) acetyl-CoA transferase (also known as ketoacyl-CoA thiolase) and yields an acetyl-CoA molecule for each cycle. Acetyl-CoA is able to enter the tricarboxylic acid (TCA) cycle which with fatty acid oxidation generates electrons forming NADH and FADH₂ which donate electrons to the electron transport chain (ETC) required for ATP synthesis Genes involved in fatty acid oxidation were measured in cumulus oocyte complexes during in vivo maturation in response to hCG. A summary of their expression pattern is depicted with blue, red and black coloured genes representing significantly up-regulated, down-regulated and unchanged respectively, as demonstrated in Figure 2.