α-Ketobutyrate decarboxylase activity in Rhizoctonia solani

The anaerobic decarboxylation of α-ketoacids by a crude extract of Rhizoctonia solani was investigated using a manometer procedure. The possible importance of this enzyme in the metabolism of the fungus is discussed. The best substrate for the enzyme preparation was α-ketobutyrate. Thiamine pyrophosphate and Mg2+ were cofactors for the enzymic decarboxylation of α-ketobutyrate. The Km for α-ketobutyrate was 7.6 × 10−3 moles/1, and the energy of activation was 3980 calories. Optimum catalysis for the reaction was achieved at 32°, pH 6.2. Products of the action of the enzyme preparation on α-ketoacids were CO2 and the respective aldehyde. Decarboxylase activity was inhibited in the presence of Hg2+, Ag+, and norjavanicin.