L Carnitine in Mitochondria Encyclopedia MDPI L carnitine is primarily synthesized in the liver from the amino acids lysine and methionine through a series of four enzymatic reactions, with the liver and kidneys converting the precursor butyrobetaine into active Carnitine: Genetic Variants Affecting Mitochondrial Energy and Health Carnitine is a friend in HFpEF and foe in HFrEF ScienceDirect Revisiting the Role of Carnitine in Heart Disease Through the Lens of the Gut Microbiota