Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis 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 Metabolic therapy for cardiovascular diseases with propionyl L carnitine ScienceDirect Mitochondrial control of fuel switching via carnitine biosynthesis Science L Carnitine Supplement: Heart Concerns Advanced Molecular Labs