L-Carnitine is a small quaternary ammonium compound, 3-hydroxy-4-trimethylammoniobutanoate, and the obligatory carrier for moving long chain fatty acids across the inner mitochondrial membrane. At 161 g/mol it is the smallest compound in the research range and the only one that is an endogenous metabolite instead of a synthetic peptide. NuVion supplies L-Carnitine as a laboratory chemical for in vitro research use only.
Key facts
| Type | Quaternary ammonium compound, endogenous metabolite |
| IUPAC name | (R)-3-hydroxy-4-(trimethylammonio)butanoate |
| Molecular formula | C7H15NO3 |
| Molecular weight | 161.2 g/mol |
| Stereochemistry | R configuration, the biologically active enantiomer |
| CAS number | 541-15-1 |
| Synonyms | Levocarnitine, vitamin BT, L-3-hydroxy-4-N-trimethylaminobutyrate |
| Supplied form | Aqueous solution, 500 mg per mL in a 20 mL vial |
L-Carnitine
$99 AUD
View productResearch use only. Not for human or veterinary use.
Structure and chemistry
L-Carnitine is a zwitterion at physiological pH. The permanently charged trimethylammonium group carries a fixed positive charge with no pKa, and the carboxylate carries a negative charge above pH 4, so the molecule has no neutral form under any biologically relevant condition. That gives it very high water solubility, effectively no membrane permeability by passive diffusion, and an absolute requirement for transporters to cross membranes. The hydroxyl at carbon three is the esterification point where fatty acyl groups attach.
Stereochemistry is central. Only the R enantiomer, levocarnitine, is a substrate for the carnitine acyltransferases. The S enantiomer is not merely inactive but competes at the transferases and at the transporter, so a racemic preparation behaves differently from an enantiopure one and enantiomeric purity is a meaningful specification for this compound. Chiral chromatography or optical rotation is the analytical method that distinguishes them, since ordinary reversed-phase HPLC and mass spectrometry cannot.
Analytically the compound is awkward for the same reasons that make it biologically distinctive. It has no chromophore, so ultraviolet detection is unavailable and quantification uses LC-MS/MS, evaporative light scattering or an enzymatic assay coupled to acetyl-CoA. Its polarity means it is poorly retained on standard C18 columns, and HILIC or ion-pairing conditions are commonly used instead. The molecule is chemically stable across a wide pH range and is not light-sensitive or oxidation-prone.
Mechanism of action
The carnitine shuttle is the mechanism. Long chain fatty acids are activated to acyl-CoA esters in the cytosol, but acyl-CoA cannot cross the inner mitochondrial membrane. Carnitine palmitoyltransferase 1, on the outer membrane, transfers the acyl group from coenzyme A to the hydroxyl of carnitine, forming acylcarnitine. The carnitine-acylcarnitine translocase then exchanges acylcarnitine inward for free carnitine outward, and carnitine palmitoyltransferase 2 on the inner membrane transfers the acyl group back to mitochondrial coenzyme A. The regenerated acyl-CoA enters beta-oxidation and the free carnitine returns to the cytosol. Carnitine palmitoyltransferase 1 is the rate-limiting step and is allosterically inhibited by malonyl-CoA, which is what links the shuttle to the cell’s lipogenic state.
A second function is buffering of the acyl-CoA pool. Because coenzyme A is present in limited quantity, accumulation of acyl groups on CoA would stall reactions that require free CoA, including pyruvate dehydrogenase and the tricarboxylic acid cycle. Transferring acyl groups onto carnitine frees CoA and exports the acyl species, so the ratio of acylcarnitine to free carnitine reports on the balance between acyl group production and oxidative capacity. That ratio is the basis for acylcarnitine profiling by tandem mass spectrometry, which is used to characterise fatty acid oxidation flux in cell models. Cellular uptake is mediated by the organic cation transporter OCTN2, a sodium-dependent carrier, and uptake can be competed with other OCTN2 substrates.
Research applications
- Fatty acid oxidation flux assays in myotube, hepatocyte or cardiomyocyte culture using radiolabelled or stable isotope labelled palmitate.
- Acylcarnitine profiling by tandem mass spectrometry to characterise the acyl-CoA to free CoA balance in cell models.
- Carnitine palmitoyltransferase 1 and 2 enzyme assays, including malonyl-CoA inhibition curves.
- Extracellular flux analysis of oxygen consumption rate with and without carnitine supplementation of the medium.
- OCTN2 transporter uptake and competition studies in transfected or native expressing cell lines.
- Reference standard for LC-MS/MS and HILIC method development on highly polar zwitterionic analytes.
L-Carnitine sits in NuVion’s Metabolism category alongside the other compounds used in energy metabolism research.
Handling in the laboratory
L-Carnitine is supplied as an aqueous solution at 500 mg per mL, so no reconstitution step is needed and the reconstitution calculator does not apply. Working dilutions are made directly into culture medium or assay buffer. The stock is concentrated and hyperosmotic, so dilution into a small assay volume is done with attention to final osmolarity, and a vehicle control matched for volume is run in parallel. Because standard culture media already contain a low background of carnitine from serum, that background is measured when absolute flux numbers matter.
Vials are kept sealed and stored as stated on the product documentation. The compound is hygroscopic in solid form and the solution is stable across a broad pH range, so the main handling considerations are aseptic withdrawal and avoiding contamination of a multi-use vial. Aliquoting at first opening avoids repeated entry. Unlike the peptides in the range, there is no oxidation or proteolysis pathway to design around, and no light protection is required.
Testing and supply from NuVion
NuVion’s L-Carnitine is manufactured at a GMP-audited facility and independently tested by Janoshik Analytical, with purity and identity confirmed by the methods appropriate to a small polar molecule. The Certificate of Analysis for a tested batch is published on the product page and in the COA library. It is supplied as a solution in sealed vials and dispatched from within Australia.
Related compounds
Other compounds used in mitochondrial and metabolic research include MOTS-c, a mitochondrial-derived peptide studied in AMPK signalling, SS-31, which associates with cardiolipin, and NAD+.
Frequently asked questions
What is L-Carnitine used for in research?
It is used in fatty acid oxidation flux work, in acylcarnitine profiling by tandem mass spectrometry, in carnitine palmitoyltransferase enzyme assays, and in transporter studies at OCTN2. It also serves as a reference standard for analytical methods on highly polar zwitterionic compounds.
Why does the L form matter?
Only the R enantiomer, levocarnitine, is a substrate for the carnitine acyltransferases. The S enantiomer competes at both the transferases and the transporter, so enantiomeric purity changes the behaviour of the preparation in an assay and cannot be assessed by ordinary reversed-phase HPLC or mass spectrometry.
Is L-Carnitine a therapeutic good in Australia?
No. NuVion’s L-Carnitine is a laboratory chemical for in vitro research. It is not included in the Australian Register of Therapeutic Goods, has not been assessed by the Therapeutic Goods Administration, and is not for human or veterinary use.
How should L-Carnitine be stored?
Vials are kept sealed and stored per the product documentation. The solution is chemically stable and needs no light protection, so the practical considerations are aseptic withdrawal and aliquoting at first opening to avoid repeated entry into a multi-use vial.
Research use only. This product is a laboratory chemical supplied for in vitro research. It is not included in the Australian Register of Therapeutic Goods and has not been assessed by the Therapeutic Goods Administration for quality, safety or efficacy. It is not for human or veterinary use, and nothing on this page is a representation about therapeutic use.
