Transports long-chain fatty acyl groups across the inner mitochondrial membrane for β-oxidation. Outer membrane: CPT1 transfers the acyl group from CoA to carnitine, producing acyl-carnitine. Inner membrane: CACT (carnitine-acylcarnitine translocase) exchanges acyl-carnitine for free carnitine. Inner matrix: CPT2 transfers the acyl group back to CoA, regenerating intramitochondrial acyl-CoA for β-oxidation. CPT1 is the regulatory step — inhibited by malonyl-CoA (the link to fatty acid biosynthesis: high malonyl-CoA → FA synthesis ON + β-oxidation OFF). Carnitine deficiency (primary genetic or secondary to valproate/pivalate antibiotics/hemodialysis) presents as hypoketotic hypoglycemia + cardiomyopathy + skeletal myopathy. Levocarnitine supplementation is therapeutic.
Organ Systems
musculoskeletal
cardiovascular
endocrine
Pathway Steps
long-chain-acyl-coa → acyl-carnitine — via CPT1 (outer mitochondrial membrane) — REGULATORY; malonyl-CoA inhibits. CPT1 on the outer mitochondrial membrane is the rate-limiting gate of fatty-acid oxidation. It is inhibited by malonyl-CoA (the fatty-acid-synthesis intermediate), so in the fed state high malonyl-CoA shuts the import gate, preventing simultaneous synthesis and oxidation.
acyl-carnitine → mitochondrial-acyl-carnitine — via CACT (carnitine-acylcarnitine translocase, inner membrane). Carnitine-acylcarnitine translocase antiports acylcarnitine inward for free carnitine outward across the inner membrane; its deficiency blocks long-chain fat oxidation, causing hypoketotic hypoglycemia and cardiomyopathy on fasting.
mitochondrial-acyl-carnitine → mitochondrial-acyl-coa — via CPT2 (inner mitochondrial leaflet) — feeds β-oxidation. CPT2 on the inner leaflet regenerates acyl-CoA for β-oxidation. CPT2 deficiency is a common cause of exertion/fasting rhabdomyolysis; only long-chain fats need this shuttle, while medium/short-chain fats enter mitochondria directly.
propionyl l carnitine (substrate) — carnitine + propionyl-CoA donor. propionyl-LC; peripheral vascular + cardiac claims; complementary to ALCAR
l carnitine l tartrate (substrate) — L-carnitine (tartrate salt). LCLT; preferred sport-supplementation form
taurine bcaa (substrate) — taurine + BCAA combination. mixed; cellular energy + protein synthesis
l carnitine (substrate) — long-chain FA mitochondrial import (CPT1/CPT2). Parent l-carnitine; CPT1 conjugates it to long-chain fatty acyl-CoA for inner-mitochondrial transport. Endogenous + dietary (red meat); supplements for primary deficiency or athletic energy claims.