Regulation of the Reduced Nicotinamide Adenine Dinucleotide Phosphate-Ferredoxin Reductase System in Clostridium kluyveri

• Published in: The Journal of biological chemistry Vol. 246; no. 4; pp. 954 - 959
• Main Authors: Thauer, Rudolf K., Rupprecht, Eckhard, Ohrloff, Christian, Jungermann, Kurt, Decker, Karl
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 25.02.1971
• Subjects: Adenine Nucleotides; Cell-Free System; Clostridium - enzymology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)62416-0

The mechanism of regulation of NADPH-ferredoxin reductase was studied in cell-free lysates of Clostridium kluyveri . The following activities, which are assumed to be linked to the enzyme, were investigated: ferredoxin reduction by NADPH, NADP + reduction by reduced ferredoxin, transhydrogenation from NADPH to NAD + , and methyl viologen reduction by NADPH. Ferredoxin reduction by NADPH is controlled by the oxidation-reduction state of the NAD + -NADH couple. NAD + is an obligatory activator (Michaelis activation constant, K a = 0.9 x 10 -4 m ), which increases V max , while the K m of the substrate NADPH ( K m = 2.25 x 10 -5 m ) remains unaffected. β-NAD + analogues can substitute to varying degrees for β-NAD + , while α-NAD + and NMN or AMP analogues are totally inactive. NADH is an inhibitor, competitive to NAD + rather than to NADPH. NADP + reduction by reduced ferredoxin is subject to product inhibition; NADPH is competitive to NADP + ( K m = 1.52 x 10 -4 m ). The transhydrogenation from NADPH to NAD + is stimulated by oxidized and inhibited by reduced ferredoxin; ferredoxin is not involved in the electron flow. Methyl viologen reduction by NADPH is not controlled by either NAD + or NADH.