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 L Carnitine 500 mg with Vitamin B 6 Medicine Center Pharmacy N Acetyl Cysteine Vs Acetyl L Carnitine? (N Acetyl Cysteine) High resolution metabolomics study revealing l homocysteine sulfinic acid, cysteic acid, and carnitine as novel biomarkers for high acute myocardial infarction risk ScienceDirect