Mechanism of one-electron oxidation of NAD(P)H and function of NADPH bound to catalase

The Linear Dependence of Log(kcat/Km) for Reduction of NAD+ by PhCH2OH on the Distance between Reactants when Catalyzed by Horse Liver Alcohol Dehydrogenase and 203 Single Point Mutants

“…The influence of Val203 on the dynamics of the EиS ground state can be best appreciated when observing the MD simulation of the LADHиPhCHOиNADH complex. The steric demand of Val203 induces an anisotropic bending of the dihydronicotinamide ring of NADH to a quasi-boat conformation with the hydrogen to be trans-SCHEME 1 ferred in the axial position facing the substrate (13,17). The quasi-boat conformation contributes to the energetic advantage (13,17) of enzymatic catalysis and is a required geometry along the pathway to the transition state.…”

Mechanisms of Protection of Catalase by NADPH

“…Because NADPH is too large to reach the latter through the relatively narrow channel leading to the heme group, electron tunneling was assumed to be the mechanism by which NADPH is able to reduce compound II to ferricatalase (18). Olson and Bruice (19) used computerized calculations, along with information from the known three-dimensional structure of bovine liver catalase, to estimate the probable route of the electron tunneling.…”

“…Olson and Bruice (19) used computerized calculations, along with information from the known three-dimensional structure of bovine liver catalase, to estimate the probable route of the electron tunneling. Others have also obtained information on the probable route of electron tunneling between the bound NADPH and the heme center of bovine or Proteus mirabilis catalase (18,34,35). Using time-resolved x-ray crystallography and single crystal microspectrometry, Gouet et al (20) determined the structure of compound I and compound II of NADPH-dependent catalase from Proteus mirabilis, including the formation and transformation of the ferryl groups.…”

“…Evidence has been presented that NADPH protects catalase by preventing and reversing the formation of an inactive form of catalase, compound II, which differs within the heme group from active catalase (12). Work in over five laboratories has provided information on how NADPH could accomplish this task (12,(15)(16)(17)(18)(19)(20). Among the difficulties in explaining the protection of catalase by NADPH is that NADPH is bound on the surface of catalase, some 20 Å from the heme, that the channel to the heme is too narrow to accommodate NADPH, and that conversion of compound II back to native catalase is a one-electron reduction step, whereas NADPH is traditionally regarded as a two-electron reducing substance.…”

Hydroxyl Radical Generation Theory: A Possible Explanation of Unexplained Actions of Mammalian Catalase

“…The radicals of amino acids within the structure of catalase were accounted specific for the reduction of compound-I to form different intermediates. These one or more unspecified amino acids, referred as DH (Rea n 8, 9 & 10) were reduced by catalase bound NADPH (NADPH b ) through the two-electron (Rea n 11) or via a pair of single-electron steps (Rea n 12 & 13) [17]. In another study [8,18], authors emphasized on the ability of endogenous donors (tyrosine or another amino acid) to be recycled through reduction by a molecule (other than NADPH) that is constantly present.…”