With a new enzymatic method, the dietary influence of oxalate, glycine, protein, and ascorbic acid on serum and urinary oxalate has been examined. Healthy and oxalate stone-forming subjects were compared. Two doses of sodium oxalate (130 and 400 mg daily) were administered. The high dose induced significant hyperoxaluria. No changes of serum oxalate were seen. Neither glycine (4.5 g daily) nor protein (50 g daily, 50% animal protein) had any effect on serum or urinary oxalate. Urinary oxalate excretion did not increase upon ingestion of large amounts of ascorbic acid (1–6 g daily), but serum oxalate levels were significantly elevated. The value of severe dietary restrictions concerning the compounds examined here seems to be questionable, as a significant increase of urinary oxalate excretion is lacking.

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.

A new enzymatic method for direct photometric determination of oxalate in serum and urine is described, using oxalate oxidase. The resulting H 2 0 2 is measured with a coupled enzyme system of catalase and aldehyde dehydrogenase. Percentage recovery of added oxalate was 99 ± 4 in serum, and 98 ± 4 in urine (n = 10). Oxalate serum levels varied from 16.9 to 44.8 μηηοΙ/L Oxalate values can be determined within 20 minutes, without time consuming pretreatment of samples. The detection limit is 5 μπιοΐ/ΐ. Direkte spektrophotometrische Bestimmung von Serum-und Urin-Oxalat mit Oxalat-OxidaseZusammenfassung: Es wird eine neue enzymatische Methode zur direkten photometrischen Bestimmung von Oxalat in Serum und Urin mittels Oxalatoxidase beschrieben. In einer gekoppelten Reaktion wird H 2 0 2 enzymatisch durch Katalase und Aldehyddehydrogenase gemessen. Die Wiederfindung von zugesetztem Oxalat betrug 99 ± 4% in Serum und 98 ± 4% in Urin (n = 10). Die Oxalatkonzentrationen in Serum variierten von 16,9 bis 44,8 /imol/l. Oxalatwerte k nnen ohne zeitraubende Probenvorbehandlung innerhalb 20 Minuten ermittelt werden. Die Erfassungsgrenze liegt bei 5 μπιοΐ/ΐ.

With a new enzymatic test using oxalate oxidase, serum and urinary oxalate can easily and quickly be determined. Serum oxalate in females was significantly higher than in males (39.5 µmol/l, 30.8 µmol/l). Increased serum levels were found only in male patients. Urinary excretion did not reveal sex-dependant differences in healthy persons. The normal range of oxalate excretion in 104 adult healthy persons was 83–365 µmol/day (95% quantile). In 130 stone formers (nonrecurrent and recurrent group) urinary oxalate excretion was found to be in the normal range. Evaluation of urinary oxalate concentration in morning samples showed increased levels in both groups of male stone formers. Oxalate concentration was unaltered in female patients.

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