Isolation and Identification of Urinary β-Aspartyl Dipeptides and Their Concentrations in Human Urine

Abstract

beta-Aspartyl-methionine, -aspartic acid and -glutamic acid and gamma-glutamyl-threonine and -glycine were isolated and identified in human urine by ion-exchange chromatography, high-voltage paper electrophoresis, acid hydrolysis and determination of N-terminal amino acids of the isolated compounds, and comparison of their behaviors in paper electrophoresis and chromatography with those of the authentic compounds. The concentrations of acidic beta-aspartyl dipeptides in human urine were determined using an amino acid analyzer. Their concentrations were as follows: beta-aspartyl-glycine, male, 44.4 +/- 8.5, female, 61.4 +/- 18.9, child, 83.7 +/- 27.1; -alanine, male, 11.0 +/- 4.9, female, 20.7 +/- 12.0, child, 25.3 +/- 9.1; -glutamic acid, male, 10.0 +/- 3.7, female, 23.0 +/- 8.5, child, 20.4 +/- 7.5; -serine, male, 9.9 +/- 2.8, female, 13.6 +/- 3.8, child, 14.9 +/- 4.7; -aspartic acid, male, 4.3 +/- 1.0, female, 9.1 +/- 2.2, child, 18.4 +/- 6.5; -threonine, male 3.9 +/- 0.9, female, 5.8 +/- 1.1, child, 13.2 +/- 4.9 mumol/g creatinine (mean +/- S.D.). The order of the sum of their concentrations tended to be child greater than female greater than male. Patients receiving intravenous hyperalimentation also excreted acidic beta-aspartyl dipeptides into urine in amounts similar to those in females and in a pattern similar to that observed in healthy persons. This finding indicates that urinary beta-aspartyl dipeptides were probably of endogenous origin because oral nutrition was stringently excluded in these patients.

Limited Accumulation of Damaged Proteins inl-Isoaspartyl (d-Aspartyl)O-Methyltransferase-deficient Mice

“…Few peptidases cleave isoaspartyl bonds, but proteolysis of the surrounding residues creates isoaspartyl-containing dipeptides and tripeptides that can be excreted in the urine (33)(34)(35)(36). Thus, if mice lacking endogenous PCMT1 do not have another repair pathway, they might excrete the damaged residues that are normally repaired in the cells of wild-type mice.…”

Identification of an Acidic Dipeptide, β‐Aspartylglycine, in the CNS of Aplysia

“…It is not known whether the aspartic acid in the acidic peptides isolated from calf brain synaptic vesicles (Lahdesmaki et al, 1977;Marnela and Lahdesmaki, 1983) are in the a-or P-configuration. On the other hand, P-DG and various other p-aspartylpeptides have been identified previously in human urine and in rat cecal contents (Buchanan et al, 1962;Lou, 1975;Tanaka and Nakajima, 1978;Welling, 1982), but have not been found in more than trace amounts in tissues. In rats the amount of cecal P-DG decreased when animals were maintained under germ-free conditions, and its formation was directly associated with intestinal flora (Welling and Groen, 1978).…”

The protein carboxymethyltransferase–dependent aspartate salvage pathway plays a crucial role in the intricate metabolic network of Escherichia coli

“…Urine contains a low concentration of aspartate, primarily in peptides ( 50 ). IsoAsp-containing peptides have also been detected in urine ( 51 ). Moreover, it was reported that the pcm gene is induced in UPEC CFT073 strain during infection of mouse urinary tract ( 52 ).…”

“…This is especially significant in environments where the primary source of aspartate is the catabolism of environmental peptides, some of which contain IsoAsp. These conditions are observed when E. coli grows in complex media, such as LB, and in natural environments such as the host urinary tract (50,51,(60)(61)(62). For instance, in human urine, the Pcmmediated aspartate salvaged from IsoAsp would increase the amount of aspartate available for cellular functioning by up to 40% (51,62).…”

“…These conditions are observed when E. coli grows in complex media, such as LB, and in natural environments such as the host urinary tract (50,51,(60)(61)(62). For instance, in human urine, the Pcmmediated aspartate salvaged from IsoAsp would increase the amount of aspartate available for cellular functioning by up to 40% (51,62). The evolutionary conservation of the Pcm enzyme raises the intriguing possibility that eukaryotic cells may also harbor a Pcmdependent aspartate-salvaging pathway, which could contribute to cellular functioning.…”