A process that occurs after the glycerides are hydrolyzed to glycerol and fatty acids. This oxidation is called p oxidation and occurs in the mitochondria. It is preceded by the transport of the fatty acid into the mitochondria via the acyl carnitine transport system. While most of the fatty acids that enter the p oxidation pathway are completely oxidized via the citric acid cycle and respiratory chain to CO2 and HOH, some of the acetyl CoA is converted to the ketones, acetoacetate, and P hydroxybutyrate. The condensation of two molecules of acetyl CoA to acetoacetyl CoA occurs in the mitochondria via the enzyme β-ketothiolase. Acetoacetyl CoA then condenses with another acetyl CoA to form HMG CoA. At last, the HMG CoA is cleaved into acetoacetic acid and acetyl CoA. The acetoacetic acid is reduced to p hydroxybutyrate, and this reduction is dependent on the ratio of NAD+ to NADH+H+^. The enzyme for this reduction, β hydroxybutyrate dehydrogenase, is tightly bound to the inner aspect of the mitochondrial membrane. Because of its high activity, the product (P hydroxybutyrate) and substrate (acetoacetate) are in equilibrium.