Pyruvate formate lyase inRhodospirillum rubrum Ha adapted to anaerobic dark conditions

The fermatation metabolism ofRhodospirillum rubrum Ha was studied after adaptation of both light-anaerobic and dark aerobic to dark anaerobic conditions.Pyruvate was metabolized to acetate, formate, CO₂ and propionate by suspensions of cells adapted to anaerobiosis. Pyruvate cleavage to formate accounted for about two-thirds of the pyruvate decomposed. This process was catalyzed by a coenzyme A dependent pyruvate formate lyase. In carboxylate- and nucleotide-free extracts, the substrate concentrations for half-maximal velocity S]_0.5V were found to be 1.5 mM for pyruvate and 75 M for coenzyme A.Pyruvate formate lyase could practically not be demonstrated in light-anaerobic photosynthesizing cells. Lyase activity was low at a basic level in darkaerobic respiring cells. After adaptation of both types of cells under growth conditions to dark anaerobiosis lyase activity increased about 10-fold. Highest levels could be observed in cells grown aerobically in the dark on pyruvate after transition to dark anaerobic conditions. It is concluded that pyruvate formate lyase is the characteristic key enzyme of the dark-anaerobic fermentative metabolism ofR. rubrum Ha.