Isolation of glycine betaine and proline betaine from human urine. Assessment of their role as osmoprotective agents for bacteria and the kidney.

Human urine is osmoprotective for enteric bacteria, permitting E. coli to grow with high concentrations of NaCl and other salts and even higher concentrations of sucrose and mannitol but not urea. The active material in urine is soluble in methanol and is precipitated by ammonium reineckate at acid pH. Using gel filtration and high-pressure liquid chromatography, we have identified two major osmoprotective compounds in urine. One is glycine betaine; the other is proline betaine as demonstrated by nuclear magnetic resonance, mass spectrum scanning, and chemical synthesis. Proline betaine has not been described previously to our knowledge in vertebrate tissues. It is known to be a cell volume-regulating agent for marine red algae and the euryhaline mollusk Elysia chloritica. We suggest that the presence of glycine and proline betaines in human urine may reflect an osmoprotective role for the kidney and that they protect bacteria in the urine only fortuitously.