As L-Carnitine Tartrate. Important Cofactor for Energy Production from Fats. 250 mg. L-Carnitine is an amino acid found in high concentrations in heart and liver tissues where inside the cells (mitochondria) L-Carnitine helps transform fats into energy. L-Carnitine also facilitates the metabolism of carbohydrates and enhances ATP (i.e. energy) production. . L-Carnitine works synergistically with Co-Q10 an antioxidant and energy co-factor found in the inner membrane of the mitochondria.