Substrate-dependent redox change

The metal ion is a typical catalyst for a reaction of Class B, but because H+ and OH- ions are formed in the process, the reaction may be expected to be pH dependent as well. The catalyst does not necessarily have to be a metal ion. Every substrate that can change oxidation state at the right potential and is capable of reacting with the hydrogen peroxide molecule in its two valency states can be considered a catalyst for this reaction. This means that the best parameter to correlate this reaction with would be the redox potential of the catalyst, which unfortunately is very difficult to measure on a solid material. The best thing to do is to use a catalyst which can be dissolved in a liquid medium of some kind, and to study the redox properties in the dissolved state. Measurements of this kind will be discussed in the section on oxidation and dehydrogenation. 

Lowe, D.J., Fisher, K., and Thomeley, R.N.F. (1993) Pre-steady-state absorbance changes show that redox changes occur in the Klebsiella pneumonia MoFe-protein that depend on substrate and components ratio a role for P-centers in reducing dinitrogen, Biochem. J. 292, 93-. 

The Fe-protein has the protein fold and nucleotide-binding domain of the G-protein family of nucleotide-dependent switch proteins, which are able to change their conformation dependent on whether a nucleoside diphosphate (such as GDP or ADP) is bound instead of the corresponding triphosphate (GTP or ATP). However, nucleotide analogues, which induce the conformational switch of the Fe-protein, do not allow substrate reduction by the MoFe-protein, nor does reduction of the MoFe-protein by other electron-transfer reagents (whether small proteins or redox dyes) drive substrate reduction. Only the Fe-protein can reduce the MoFe-protein to a level that allows it to reduce substrates such as... 

The electrochemical properties of redox-active substrates are also affected on binding to a receptor molecule. This is the case for the complexation of metal hexacyanides by polyammonium macrocycles where the shift of the redox potential depends on the binding constants and the oxidation or reduction of the substrates leads to pronounced changes in stability (see Chapter 3) [3.21, 3.22]. 

Aldehyde oxidase purified from maize coleoptiles is a multicomponent enzyme that contains a molybdenum cofactor, nonheme iron, and flavin adenine dinucleotide (FAD) as prosthetic groups.111 When substrate specificity of the aldehyde oxidase was tested, good activity was detected with IAAld, indole-3-aldehyde, and benzaldehyde among others. The addition of NADP and NADPH did not change the activity. In contrast, in maize endosperm, tryptophan-dependent IAA biosynthesis was dependent on an NADP/NADPH redox system, which may mean that the two tissues of maize are utilizing different pathways or different redox systems for IAA biosynthesis.112... 

It appears from the description of radical ions in Sects. 1 and 3 that redox reactions can significantly change the chemical and physical properties of conjugated 7r-systems. Whether the extended jc-species are treated within molecular orbital theory or within band-structure theory, the inherent assumption in these concepts is that an electron transfer is reversible and does not promote subsequent chemical reactions. While inspection of cyclic voltammetric waves and the spectroscopic characterization of the redox species provide reliable criteria for the reversibility of an electron transfer and the maintenance of an intact (T-frame, it is generally accepted that electron transfer, depending on the nature of the substrate and on the experimental conditions, can also initiate chemical reactions under formation or cleavage of er-bonds [244, 245],... 

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