Peroxidase content of soybean root nodules.

A peroxidase has been isolated from soybean nodules and its main characteristics have been determined. Its molecular weight (48 000) and spectral properties are similar to those of usual plant peroxidases. Its activity is comparable to that of low-efficiency plant peroxidases. The rate constant of the reaction with H2O2 is 3 x 10(5) M-1 x s-1. In this reaction, nodule peroxidase yields an oxidized intermediate analogous to the compound I species of peroxidases already studied. A comparison is made with the pseudoperoxidatic activity of soybean leghemoglobin components. Leghemoglobins a and c react with H2O2 with rate constants of 5 x 10(3) and 2.5 x 10(3) M-1 x s-1, respectively, yielding the leghemoglobin (IV) species. During these reactions leghemoglobins are inactivated.