Identification of histidylleucine and other histidyl peptides as normal constituents of human urine

Abstract

In order to examine the possibility that the urinary excretion of histidylleucine might reflect the in vivo biogenesis of angiotensin, a technique has been devised for the detection of histidyl peptides in normal human urine. The peptides are isolated by displacement procedures on ion-exchange resins and further analyzed by paper and ion-exchange column chromatography. Histidyl peptides have been quantitated by fluorescence analysis after reaction with o-phthalaldehyde. Histidylleucine, in quantities of about 5–25 μg, has been shown to be present in 24-hour collections of human urine. The peptide isolated from urine has been found to be identical with synthetic material in comparisons using high resolution ion-exchange chromatography, paper chromatography in four solvent systems, acid hydrolysis followed by amino acid analysis, and fluorescence spectrum. A histidyl peptide which was regularly present, usually in somewhat larger quantities, was a tripeptide with sequence His-Leu-Gly or His-Gly-Leu. Numerous other histidyl peptides were present in smaller amounts but did not correspond to any of several other simple histidyl dipeptides examined and were not further identified.