title: Identification of N-beta-L-aspartyl-L-phenylalanine as a normal constituent of human plasma and urine.
abstract: A new beta-aspartyl dipeptide, N-beta-L-aspartyl-L-phenylalanine (beta-AP), has been isolated and identified in urine and plasma from normal human volunteers. beta-AP was isolated from urine samples by high performance liquid chromatography (HPLC). Its identity and stereochemistry were demonstrated by HPLC and gas chromatography/mass spectrometry (GC-MS). The mean urinary beta-AP concentration in the subjects was 0.63 +/- 0.14 microgram/mg creatinine when averaged over two consecutive days of urine collection. Daily beta-AP excretion, determined from two 24-h urine samples collected from five individuals, was 801 +/- 117 micrograms/d (2.7 mumol/d). No diurnal rhythm was evident within the 24-h collection periods. beta-AP was also isolated from human plasma by HPLC and identified by GC-MS. Plasma from subjects contained approximately 5 ng beta-AP/ml. Furthermore, beta-AP was formed when asparagine and phenylalanine were incubated with an enzyme extract from human kidney. Thus, at least some of the beta-AP present in humans, and presumably other beta-aspartyl dipeptides as well, appears to be synthesized endogenously.
authors.affiliation: Department of Drug Metabolism, G. D. Searle & Co., Skokie, IL 60077.
authors.forename: E G
authors.initials: EG
authors.lastname: Burton
authors.forename: G L
authors.initials: GL
authors.lastname: Schoenhard
authors.forename: J A
authors.initials: JA
authors.lastname: Hill
authors.forename: R E
authors.initials: RE
authors.lastname: Schmidt
authors.forename: J D
authors.initials: JD
authors.lastname: Hribar
authors.forename: F N
authors.initials: FN
authors.lastname: Kotsonis
authors.forename: J A
authors.initials: JA
authors.lastname: Oppermann
mesh_terms: D001224:Aspartic Acid / Q000378:metabolism / Q000652:urine; D002851:Chromatography, High Pressure Liquid; D002940:Circadian Rhythm; D004151:Dipeptides / Q000096:biosynthesis / Q000097:blood / Q000652:urine*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism; D013058:Mass Spectrometry; D009994:Osmolar Concentration; D010649:Phenylalanine / Q000378:metabolism / Q000652:urine; D012016:Reference Values
chemical_list: D004151:Dipeptides; C045207:aspartyl-phenylalanine; D001224:Aspartic Acid; D010649:Phenylalanine