Determination of Oxalate and Oxaloacetate

The determination of oxalate in urine is required for diagnosis of renal calculus and hyperoxaluria. For enzymatic oxalate determination, oxalate decarboxylase (EC 4.1.1.2) has been employed in enzyme thermistors (Danielsson etal., 1981), enzyme reactors (Lindberg, 1983), and potentiometric enzyme electrodes (Kobos and Ramsey, 1980). 

Alternatively, oxalate oxidase (EC 1.2.3.4) can be used, which catalyzes the following reaction  

It is evident from the equation that potentiometric CO2 electrodes as well as amperometric O2 or H2O2 electrodes can be used as transducers. Both potentiometric and amperometric sensors have been covered by a layer of oxalate oxidase protected by a dialysis membrane (Bradley and Rechnitz, 1986 Rahni et al.f 1986a). The sensors had a pH optimum at pH 3.5-4. Diffusion control was reached at 1 U oxalate oxidase per electrode. Oxalate determination was not affected by ascorbic acid or amino acids. The hydrogen peroxide-detecting sensor (Rahni et al., 1986a) has been used to measure oxalate in urine diluted 1 40. 

Enzyme sensors for oxaloacetate are based on immobilized oxalo-acetate decarboxylase (EC 4.1.1.3) and have been applied to the determination of aspartate aminotransferase (see Section 3.2). Ho and Rechnitz (1987) suggested combining partially quarternized polyethyl-eneimine catalyzing the reaction  

---