Regulation of the Reduced Nicotinamide Adenine Dinucleotide Phosphate-Ferredoxin Reductase System in Clostridium kluyveri
1971; Elsevier BV; Volume: 246; Issue: 4 Linguagem: Inglês
10.1016/s0021-9258(18)62416-0
ISSN1083-351X
AutoresRudolf K. Thauer, E. Rupprecht, Christian Ohrloff, Kurt Jungermann, K. Decker,
Tópico(s)Metal-Catalyzed Oxygenation Mechanisms
ResumoThe 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, NADPf 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, & = 0.9 X 10e4M), which increases V,,,, while the K, of the substrate NADPH (Km = 2.25 X 1O-5 x) remains unaffected.&NAD+ analogues can substitute to varying degrees for ,& NAD+, while a(-NAD+ and NMN or AMP analogues are totally inactive.NADH is an inhibitor, competitive to NADf rather than to NADPH.NADP' reduction by reduced ferredoxin is subject to product inhibition; NADPH is competitive to NADP+ (K, = 1.52 X 10-4M).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.
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