A comparison of horseradish peroxidase and manganese ions as catalysts for the oxidation of dihydroxyfumaric acid.

With horseradish peroxidase as catalyst the main product was dihydroxytartrate, but small amounts of glycolaldehyde, mesoxalic semialdehyde, mesoxalate and possibly glyoxal were also formed. Mn(2+) catalysis gave rise only to mesoxalate and oxalate. When oxygen uptake was followed by a manometric method the rate of the peroxidase-catalysed reaction was proportional to oxygen concentration and marked inhibition by cyanide was obtained only at low buffer concentration. The catalytic effects of peroxidase and Mn(2+) were almost always additive. Chelating agents inhibited the Mn(2+)-catalysed reaction, but had either no effect or a slight accelerating effect on the peroxidase-catalysed reaction. It is concluded that Mn(2+) does not function as cofactor in the peroxidase-catalysed oxidation.