Revisiting the Role of Carnitine in Heart Disease Through the Lens of the Gut Microbiota 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 What is the role of carnitine (L carnitine) in the management of heart failure? Blood carnitine as a biomarker for acute myocardial infarction.