Arginine & Citrulline 500 mg/250 mg, 240 Veg Capsules, NOW FoodsNow Foods Arginine & Citrulline Supports Protein Metabolism. Helps Maintain Muscle Tissue. Dietary Supplement. Arginine and Citrulline are two amino acids that are integral to protein metabolism and utilization, as well as to the maintenance of muscle tissue. Both are key intermediates in the urea cycle, where they participate in the detoxification of ammonia via the production of urea. In addition, any arginine not converted to urea enters general