Summary
Carnitine is a quaternary ammonium compound involved in metabolism in most mammals, plants, and some bacteria. In support of energy metabolism, carnitine transports long-chain fatty acids from the cytosol into mitochondria to be oxidized for free energy production, and also participates in removing products of metabolism from cells. Given its key metabolic roles, carnitine is concentrated in tissues like skeletal and cardiac muscle that metabolize fatty acids as an energy source. Generally individuals, including strict vegetarians, synthesize enough L-carnitine in vivo. Carnitine exists as one of two stereoisomers (the two enantiomers -carnitine (S-(+)-) and -carnitine (R-(−)-)). Both are biologically active, but only -carnitine naturally occurs in animals, and -carnitine is toxic as it inhibits the activity of the -form. At room temperature, pure carnitine is a whiteish powder, and a water-soluble zwitterion with relatively low toxicity. Derived from amino acids, carnitine was first extracted from meat extracts in 1905, leading to its name from Latin, "caro/carnis" or flesh. Some individuals with genetic or medical disorders (such as preterm infants) cannot make enough carnitine, requiring dietary supplementation. Despite common carnitine supplement consumption among athletes for improved exercise performance or recovery, there is insufficient high-quality clinical evidence to indicate it provides any benefit. carnitine biosynthesis Many eukaryotes have the ability to synthesize carnitine, including humans. Humans synthesize carnitine from the substrate TML (6-N-trimethyllysine), which is in turn derived from the methylation of the amino acid lysine. TML is then hydroxylated into hydroxytrimethyllysine (HTML) by trimethyllysine dioxygenase (TMLD), requiring the presence of ascorbic acid and iron. HTML is then cleaved by HTML aldolase (HTMLA, a pyridoxal phosphate requiring enzyme), yielding 4-trimethylaminobutyraldehyde (TMABA) and glycine. TMABA is then dehydrogenated into gamma-butyrobetaine in an NAD+-dependent reaction, catalyzed by TMABA dehydrogenase.
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Related publications (6)

Nicotinamide riboside supplementation alters body composition and skeletal muscle acetylcarnitine concentrations in healthy obese humans

Johan Auwerx, Richardus Houtkooper

Background: Nicotinamide riboside (NR) is an NAD(+) precursor that boosts cellular NAD(+) concentrations. Preclinical studies have shown profound metabolic health effects after NR supplementation. Objectives: We aimed to investigate the effects of 6 wk NR ...
OXFORD UNIV PRESS2020

Inkjet Printed Carbon Nanotube Electrodes for Measuring Pyocyaninand Uric Acid in a Wound Fluid Simulant and Culture Media

Hubert Girault, Andreas Stephan Lesch, Milica Jovic

Polyacrylamide-coated, carbon nanotube (PA/CNT)electrodes were prepared by an ink-jet printing process and used to measure pyocyanin and uric acid in a wound fluid simulant at 37 oC.These two moleculesare potential indicators of infection and therefore the ...
2019
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