Measurement of Urinary Free γ-Carboxyglutamic Acid by High Performance Amino Acid Analysis

Abstract

The measurement of free γ-Carboxyglutamic acid (Gla) in urine was examined. After separation of Gla from whole urine by anion exchange chromatography, the eluent was concentrated by evaporation and subsequently physio-ogical fluid analysis was performed by Hitachi high performance amino acid analyzer (type835-50) using lithium citrate buffer (Li 0-15N, pH 2.3) as eluant. Gla peak was eluted at 18 minutes. The precision with 10 nmole /50μl of Gla by this method was 0.86-2-52%in CV. Recovery in the anion exchange concentration step 85.9-93.5% and recovery of Gla added to urine was 97.3%. The values obtained by this amino acid analysis correlated well with those by high performance liquid chromatography in 17patients with urolithiasis (r=0.95).
In 11 male calcium stone formers. urinary free Gla excretion ranged from 25-2 to 43.8μmole/24h (37.3±5.4, Mean±SD) and 19 normal male adults excreted from 35.6to62.4μmole Of Gla per day (46.9±7.4, Mean±SD). AS Urinary free Gla excretion is SignifiCantly decreased in calcium stone formers compared to normal adults, the urinary free Gla seems to be an inhibitory factor in calcium stone formation. However, further studies are needed to draw a definite conclusion.