Enzymatic oxalate determination in urine.

1THE ACCURATE MEASUREMENT of oxalate concentration in urine presents considerable difficulties. The methods available in the literature are based upon either the direct formation of calcium oxalate precipitate and subsequent oxidimetric titration (1-3) or upon a preliminary ether extraction followed by a titrimetric procedure (4, .5). In a more elaborate method, the extraction with ether is combined with a colonmetric determination (6). Perhaps the most reliable approach devised to date employs radioactive-labeled oxalic acid (7), but this procedure involves special equipment not available in many laboratories. This report describes a rapid method for the determination of oxalic acid in urine utilizing the oxalic decarboxylase from the wood-rot fungus Coilybia velutipes and originally suggested by Dr. H. Shimazono. Oxalic acid is stoichiometrically converted to formic acid and CO2 according to the reaction (8)