Carnitine plays a crucial role in transporting long-chain fatty acids into the mitochondria for β-oxidation. Fatty acids cannot cross the mitochondrial membrane freely; they require conversion to acyl-carnitine by carnitine palmitoyltransferase I (CPT I). This complex is shuttled across the inner mitochondrial membrane, where carnitine palmitoyltransferase II (CPT II) regenerates acyl-CoA for energy production. Without carnitine, fatty acid breakdown and subsequent ATP generation are severely impaired, affecting energy homeostasis especially during fasting or increased energy demand. This function is essential for sustaining muscle and hepatic metabolism.

Reference: Principles of Biochemistry, Lehninger, 7th Edition.