Determination of Urinary Oxalate with Cl− and NO−3 Insensitive Oxalate Oxidase Purified from Sorghum Leaf

Abstract

Methods for determination of urinary oxalate, which use oxalate oxidase from mosses, barley, banana peel, and beet stems, may suffer interference from physiological concentrations of Cl− and NO−3, usually found in urine (1)(2)(3)(4)(5)(6). The usual daily excretion of Cl− and NO−3 are 10–15 g/day and 0.5 g/day, respectively. The potential interference of these anions is removed either by passing the urine through an ion-exchange column or by precipitation of oxalate from urine and its redissolution prior to oxalate assay (1)(7). This pretreatment complicates the procedure; consequently, the sensitivity and reproducibility of the determination often suffer. In our laboratory, we have purified an oxalate oxidase from leaves of 10-day-old seedling plants of grain sorghum (CSH-5), which is insensitive to physiological concentrations of Cl− and NO−3 (8). In the present report, we describe a new method of oxalate determination using grain sorghum leaf enzyme, which does not suffer from Cl− and NO−3 interference. The seeds of grain sorghum ( Sorghum vulgare var CSH-5) were a gift from M/s Nath Seeds Ltd. (Aurangabad, India). The 10-day-old seedling plants were raised from these seeds in the laboratory according to our method published previously (8). The leaves were collected and …