Determination of Oxalate in Urine Using Oxalate Oxidase: Comparison with Oxalate Decarboxylase

Abstract

The oxalate content of urine is determined by means of oxalate oxidase and simple pH measurement. The enzyme specifically decarboxylates oxalate, producing two moles CO 2 per mole oxalate. The CO 2 diffuses into an alkaline buffer solution (Hallson, P. C. & Rose, G. A. (1974), Clin. Chim. Acta 55, 29-39) in the closed reaction vessel, and reduces the pH value, which is measured with an electrode. Only 125 native urine is required to measure oxalate concentrations in the range of 80 / to 1.6 mmol/1 (corresponding to 7 to 144 mg anhydrous oxalic acid per liter). The limit of detection is 10 nmol oxalate, and the accuracy is 101% with a coefficient of variation of 6%.The method described is insensitive to various interfering factors, such as reducing and oxidizing substances, cloudy or colored samples. It is therefore also suitable for oxalate determination in food technology and plant breeding. Bestimmung von Oxalat in Urin mit OxalafrOxidase: Vergleich mit Oxalat-DecarboxylaseZusammenfassung: Der Oxalatgehalt von Urin wird mittels Oxalat-Qxidase durch einfache pH-Messung bestimmt. Das Enzym decarboxyltert spezifisch Oxalat, wobei je Mol Oxalat zwei Mol CO 2 entstehen. Durch Diffusion des CO 2 in eine alkalische Pufferlösung (Hallson, P. C. & Rose, G. A. (1974), Clin. Chim. Acta 55, 29-39) in geschlossenen Reaktionsgefäßen erniedrigt sich der pH-Wert, der mit einer Elektrode gemessen wird. Dabei genügen 125 Nativ-Urin, um Oxalatkonzentrationen im Meßbereich von 80 / bis 1,6 mmol/1 (entsprechend 7 mg bis 144 mg wasserfreie Oxalsäure je 1) zu erfassen. Die Nachweisgrenze liegt bei 10 nmol Oxalat, die Richtigkeit beträgt 101% bei einem Variationskoeffizienten von 6%. Die beschriebene Methode zeichnet sich durch geringe Störanfälligkeit gegenüber verschiedenartigen Analysenproben aus. Reduzierende und oxidierende Substanzen, trübes und gefärbtes Untersuchungsmaterial stören nicht. Sie ist deshalb auch für Oxalatbestimmungen in der Lebensmitteltechnologie und Pflanzenzüchtung geeignet.

Determination of plasma oxalate with oxalate oxidase

“…Bovine liver catalase (EC 1.11.1.6, 65000 U/mg) was obtained from Serva GmbH (Heidelberg, FRG), diluted 1 : 9 (130000 U/ml), and stored in portions at -20°C. Oxalate oxidase (EC 1.2.3.4) was purified from barley seedlings by the method of Kohfbecker et al [19] and Chiriboga [20]. The final purification was done on a 2.6 x 40 cm DEAE-Sepharose CL&B column (Pharmacia, Uppsala, Sweden), and enzyme activity in the fractions was assessed with guajacol and peroxidase (EC 1.11.1.7) [21].…”

Dietary Influence on Serum and Urinary Oxalate in Healthy Subjects and Oxalate Stone Formers

“…Analytical Procedures. Oxalate was analyzed by a new enzymatic method recently described (17,18). Ascorbate was determined with a modified method according to Zannoni et al (25).…”

Direct Spectrophotometric Determination of Serum and Urinary Oxalate with Oxalate Oxidase

“…Using modified reaction vessels and substituting decarboxylase by oxidase, we achieved higher sensitivity and accuracy for the method (11). However, oxalate can only be measured after an incubation time of at least 16 hours.…”

“…If CO 2 is measured, the assay is twice as sensitive as that based on the decarboxylation (11). However, there are difficulties in the determination of oxalate in serum, especially with regard to the high endogeneous concentration of CO 2 .…”