L-citrulline is the L-enantiomer of citrulline. It has a role as a micronutrient, a protective agent, a nutraceutical, an EC 1.14.13.39 (nitric oxide synthase) inhibitor, a mouse metabolite, a Saccharomyces cerevisiae metabolite, an Escherichia coli metabolite and a human metabolite. It is an enantiomer of a D-citrulline. It is a tautomer of a L-citrulline zwitterion.