Carnitine palmitoyltransferase II

Carnitine palmitoyltransferase II (CPT II) is a mitochondrial enzyme involved in the metabolism of long-chain fatty acids. It plays a crucial role in the transport of long-chain fatty acids from the cytoplasm into the mitochondria for beta-oxidation, a process by which fatty acids are broken down to generate ATP, the primary energy currency of the cell. CPT II, together with Carnitine palmitoyltransferase I (CPT I), forms part of the carnitine shuttle system, which is essential for the fatty acid oxidation pathway.

Function

CPT II is located on the inner mitochondrial membrane and is responsible for the reconversion of acyl-carnitine back to acyl-CoA and free carnitine, inside the mitochondria. This step is critical for the continuation of the beta-oxidation cycle. The enzyme thus facilitates the utilization of fatty acids as an energy source, especially during periods of fasting, exercise, or other conditions when carbohydrates are not readily available.

Genetics

The gene encoding CPT II is located on chromosome 1p32. It is expressed in many tissues, including liver, kidney, and muscle. Mutations in the CPT II gene can lead to Carnitine palmitoyltransferase II deficiency, a metabolic disorder that affects the body's ability to oxidize long-chain fatty acids. This deficiency can present in several forms, ranging from a severe neonatal onset with multi-organ failure to a milder adult-onset myopathic form characterized by muscle weakness and pain.

Clinical Significance

Carnitine palmitoyltransferase II deficiency is one of the most common causes of hereditary myopathy and recurrent rhabdomyolysis. The condition can be triggered by prolonged exercise, fasting, or other stressors that increase the demand for fatty acid oxidation. Diagnosis is typically made through a combination of clinical presentation, biochemical tests showing elevated muscle enzymes in the blood, and genetic testing. Treatment focuses on dietary management to avoid long-chain fat intake, supplementation with medium-chain triglycerides (MCTs), and avoidance of fasting and other triggering factors.

Research Directions

Research into CPT II and its associated disorders continues to evolve. Studies are exploring the molecular mechanisms underlying the enzyme's function, the pathophysiology of CPT II deficiency, and potential therapeutic strategies, including gene therapy and novel pharmacological approaches to enhance fatty acid oxidation or compensate for the enzyme's deficiency.

See Also

• Fatty acid metabolism
• Mitochondrion
• Beta-oxidation
• Carnitine palmitoyltransferase I deficiency