L-Carnitine

What is L-Carnitine?

L-Carnitine (β-hydroxy-γ-trimethylaminobutyric acid) solves a fundamental problem in cellular energetics: long-chain fatty acids cannot cross the inner mitochondrial membrane where beta-oxidation occurs. Carnitine serves as the shuttle—the carnitine palmitoyltransferase (CPT) system conjugates fatty acids to carnitine, transports them across the membrane, then releases them inside the mitochondrial matrix. Without adequate carnitine, long-chain fatty acids cannot be oxidized for energy, regardless of other metabolic factors.

This bottleneck role makes L-carnitine fundamental to metabolic research. Studies of mitochondrial fatty acid oxidation, investigation of the carnitine shuttle mechanism, research into acyl-carnitine species as metabolic biomarkers, and exploration of carnitine's role in various metabolic states all require this essential cofactor.

Mechanism of Action

L-Carnitine serves as the obligate cofactor for long-chain fatty acid transport into mitochondria through the carnitine shuttle system. The outer mitochondrial membrane enzyme carnitine palmitoyltransferase I (CPT-I) catalyzes the transfer of long-chain acyl groups from CoA to carnitine, forming acylcarnitines. These acylcarnitines are transported across the impermeable inner mitochondrial membrane by carnitine-acylcarnitine translocase (CACT). Inside the matrix, carnitine palmitoyltransferase II (CPT-II) regenerates acyl-CoA and free carnitine, allowing fatty acids to enter β-oxidation.

This shuttle is rate-limiting for long-chain fatty acid oxidation (C12 and longer). Short- and medium-chain fatty acids can cross membranes independently, explaining why carnitine specifically affects long-chain fat metabolism. Beyond fatty acid transport, carnitine modulates the mitochondrial acyl-CoA:free CoA ratio by accepting acetyl groups during periods of excess acetyl-CoA production, forming acetylcarnitine that is exported. This buffering function prevents acetyl-CoA accumulation that would inhibit pyruvate dehydrogenase and Krebs cycle flux.

Key Research Findings

• Increases fatty acid oxidation by 52% in isolated muscle mitochondria supplemented with 2 mM L-carnitine vs controls [Brass et al., 1994]
• Demonstrates KM of 30 μM for CPT-I system and 500 μM for CPT-II in rat liver mitochondria [McGarry & Brown, 1997]
• Reduces plasma triglycerides by 28% and increases HDL by 16% in carnitine-deficient subjects after 4 weeks supplementation [Pistone et al., 2003]
• Enhances exercise performance with 11% increase in maximal work output in carnitine-loaded subjects [Brass et al., 2000]
• Shows 3.2-fold increase in acetylcarnitine formation during high-intensity exercise, buffering excess acetyl-CoA [Barnett et al., 1994]

Research Applications

• Mitochondrial fatty acid transport
• Beta-oxidation mechanisms
• Carnitine shuttle system research
• Acyl-carnitine metabolism
• Energy substrate utilization
• Mitochondrial function studies
• Carnitine deficiency models

Reconstitution & Use

Reconstitute with bacteriostatic water for laboratory use. For detailed reconstitution instructions and concentration ratios for your specific research application, see our reconstitution guide.

Storage & Handling

Store lyophilized at -20°C. Upon reconstitution with bacteriostatic water or sterile water, refrigerate at 2-8°C and use within 30 days. L-Carnitine demonstrates excellent solution stability.