Carnitine
<p><b>Carnitine</b> is a <a href="http://en.wikipedia.org/wiki/Quaternary_ammonium_cation" title="Quaternary ammonium cation">quaternary ammonium compound</a> biosynthesized from the <a href="http://en.wikipedia.org/wiki/Amino_acids" title="Amino acids" class="mw-redirect">amino acids</a> <a href="http://en.wikipedia.org/wiki/Lysine" title="Lysine">lysine</a> and <a href="http://en.wikipedia.org/wiki/Methionine" title="Methionine">methionine</a>.<sup id="cite_ref-1" class="reference"><a href="http://en.wikipedia.org/wiki/L-carnitine#cite_note-1">[1]</a></sup> In living cells, it is required for the transport of <a href="http://en.wikipedia.org/wiki/Fatty_acid" title="Fatty acid">fatty acids</a> from the <a href="http://en.wikipedia.org/wiki/Cytosol" title="Cytosol">cytosol</a> into the <a href="http://en.wikipedia.org/wiki/Mitochondria" title="Mitochondria" class="mw-redirect">mitochondria</a> during the breakdown of <a href="http://en.wikipedia.org/wiki/Lipid" title="Lipid">lipids</a> (fats) for the generation of metabolic energy. It is widely available as a <a href="http://en.wikipedia.org/wiki/Nutritional_supplement" title="Nutritional supplement" class="mw-redirect">nutritional supplement</a>. Carnitine was originally found as a <a href="http://en.wikipedia.org/wiki/Growth_factor" title="Growth factor">growth factor</a> for <a href="http://en.wikipedia.org/wiki/Mealworms" title="Mealworms" class="mw-redirect">mealworms</a> and labeled <a href="http://en.wikipedia.org/wiki/Vitamin" title="Vitamin">vitamin</a> B<sub>T</sub>,<sup id="cite_ref-2" class="reference"><a href="http://en.wikipedia.org/wiki/L-carnitine#cite_note-2">[2]</a></sup> although carnitine is not a proper <a href="http://en.wikipedia.org/wiki/Vitamin" title="Vitamin">vitamin</a>.<sup id="cite_ref-3" class="reference"><a href="http://en.wikipedia.org/wiki/L-carnitine#cite_note-3">[3]</a></sup> Carnitine exists in two <a href="http://en.wikipedia.org/wiki/Stereoisomer" title="Stereoisomer" class="mw-redirect">stereoisomers</a>: Its biologically active form is <small>L</small>-carnitine, whereas its <a href="http://en.wikipedia.org/wiki/Enantiomer" title="Enantiomer">enantiomer</a>, <small>D</small>-carnitine, is biologically inactive.<sup id="cite_ref-4" class="reference"><a href="http://en.wikipedia.org/wiki/L-carnitine#cite_note-4">[4]</a></sup></p>