Improved determination of D-glucaric acid in urine.

Using a simplex optimization procedure, we have elaborated a sensitive and reliable micromethod for determining D-glucaric acid, based on inhibition of glucuronidase activity by 1,4-D-glucarolactone, produced from D-glucaric acid by heating. The maximum attainable difference between glucuronidase activity in the reaction mixture with and without D-glucaric acid was used as an optimization criterion. From the optimization scheme, 1 mmol/L 4-nitrophenyl-beta-D-glucuronide and pH 5.0 were found to be optimal conditions for determination of D-glucaric acid with this test. In contrast to other similar methods, in which a logarithmic calibration curve is used, we calculate D-glucaric acid with a linear calibration curve by using the Dixon (Biochem. J. 55: 170, 1953) plot. The coefficient of variation for the method (within-run and between-day precision) was from 3.1 to 5.8%. Men excrete more D-glucaric acid than do women per 24 hours, but we saw no sex-related differences in excretion of D-glucaric acid when it was expressed in terms of urinary creatinine.