REDUCTION OF PYRROLOQUINOLINE QUINONE BY DT-DIAPHORASE FROM CLOSTRIDIUM KLUYVERI

Reduction of pyrroloquinoline quinone (PQQ) by DT-diaphorase in Clostr idium kluyveri was investigated. During the incubation of 50 mu M pQQ, 100 mu M NADH and DT-diaphorase in 50 mM potassium phosphate buffer a t pH 7.4, the increase of absorbance at 302 nm and the shift of absorp tion maximum from 490 nm to 510 nm was clearly observed as indication of its reduction under anaerobic conditions. The apparent Km and Vmax values for PQQ were 70.9 mu M and 11.1 mu mol/min/mg protein, respecti vely. The reduction of PQQ taking place in the enzyme mixture was supp ressed almost completely by dicumarol, a specific inhibitor for DT-dia phorase. The present study suggests that DT-diaphorase serves to reduc e PQQ and protect it from formation of irreversible Schiff base linkag es in vivo.