Which of the following is NOT a component of ketone bodies?

Ketone bodies are metabolic products that arise primarily in the liver during periods of fasting, carbohydrate-restricted diets, or prolonged exercise. They include three main compounds: acetoacetate, β-hydroxybutyrate (often referred to as D-β-hydroxybutyrate), and acetone. These compounds are utilized by various tissues, including the brain and muscle, as an alternative energy source when glucose is in short supply.

Acetoacetate is the first ketone body synthesized from fatty acids, and it can be converted into the other two forms. D-β-hydroxybutyrate is derived from acetoacetate through the action of an enzyme that reduces acetoacetate, while acetone is a product of the non-enzymatic decarboxylation of acetoacetate, which occurs to some extent but is less metabolically significant.

Propionyl-CoA, however, is not considered a ketone body. It is a metabolic intermediate involved in the metabolism of certain fatty acids and amino acids, particularly those containing odd carbon chains. It can enter the citric acid cycle after being converted to succinyl-CoA but is not produced from the ketogenesis pathway.

Thus, the