Chapter 1
Redox Proteins and Bioelectrocatalysis
Abstract This chapter starts by introducing the basic feature and thermodynamics of
redox proteins including redox enzymes (oxidoreductases). Biochemical properties
of organic and inorganic redox components in redox enzymes are detailed, and they
are very important to understand bioelectrocatalysis. This chapter also introduces
the basic concept of bioelectrocatalysis.
Keywords Biological redox potential · Organic cofactors · Metallic ion cofactors ·
Hydride ion transfer · Electron transfer · Bioelectrocatalysis
1.1 Oxidoreductases [1, 2]
Oxidoreductases (redox enzymes) are concerned with widespread biological electron
transfers, i.e. processes of respiration, fermentation, and photosynthesis to catalyze
electron transfer reactions across the tree of life and to facilitate biologically driven
fluxes of several essential elements such as hydrogen, carbon, nitrogen, oxygen, and
sulfur on Earth [3]. The kinds of the redox enzymes are approximately one-quarter of
all known enzymes based on the enzyme nomenclature [4]. The name of the majority
of the redox enzymes is dehydrogenase, although sometimes reductase is used as an
alternative. The first class of dehydrogenases that we shall meet are the enzymes that
strictly utilize β-nicotine amide dinucleotide (phosphate) (NAD(P)) as a coenzyme
and are called NAD(P)-dependent dehydrogenases. NAD(P)(H) shuttles back and
forth between the NAD(P)-dependent enzyme and solution to transfer hydride ion
(two-electron and single-proton, analogous to BH 4
− and AlH 4
− ). The specificity to
NAD(P) is very rigid in NAD(P)-dependent enzymes. Other than these, NAD(P)independent dehydrogenases including flavoproteins, quinoproteins, and metalloproteins utilize not NAD(P) but other redox compounds including redox proteins.
NAD(P)-independent dehydrogenases catalyze the transfer of electron and/or hydride
ion. NAD(P)-reducing dehydrogenases (e.g. NAD(P)-reducing hydrogenase (H 2 ase)
and NAD(P)-linked molybdenum (Mo)- (or tungsten (W)-)containing formate dehydrogenase (FoDH)) utilize NAD(P)
+ as an electron acceptor, but NAD(P)
+ can be
replaced with other oxidizing compounds with electron-transfer property, because
they have a flavin-containing diaphorase subunit that can catalyze both electron
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
K. Kano et al., Enzymatic Bioelectrocatalysis,
https://doi.org/10.1007/978-981-15-8960-7_1
1
Redox Proteins and Bioelectrocatalysis
Abstract This chapter starts by introducing the basic feature and thermodynamics of
redox proteins including redox enzymes (oxidoreductases). Biochemical properties
of organic and inorganic redox components in redox enzymes are detailed, and they
are very important to understand bioelectrocatalysis. This chapter also introduces
the basic concept of bioelectrocatalysis.
Keywords Biological redox potential · Organic cofactors · Metallic ion cofactors ·
Hydride ion transfer · Electron transfer · Bioelectrocatalysis
1.1 Oxidoreductases [1, 2]
Oxidoreductases (redox enzymes) are concerned with widespread biological electron
transfers, i.e. processes of respiration, fermentation, and photosynthesis to catalyze
electron transfer reactions across the tree of life and to facilitate biologically driven
fluxes of several essential elements such as hydrogen, carbon, nitrogen, oxygen, and
sulfur on Earth [3]. The kinds of the redox enzymes are approximately one-quarter of
all known enzymes based on the enzyme nomenclature [4]. The name of the majority
of the redox enzymes is dehydrogenase, although sometimes reductase is used as an
alternative. The first class of dehydrogenases that we shall meet are the enzymes that
strictly utilize β-nicotine amide dinucleotide (phosphate) (NAD(P)) as a coenzyme
and are called NAD(P)-dependent dehydrogenases. NAD(P)(H) shuttles back and
forth between the NAD(P)-dependent enzyme and solution to transfer hydride ion
(two-electron and single-proton, analogous to BH 4
− and AlH 4
− ). The specificity to
NAD(P) is very rigid in NAD(P)-dependent enzymes. Other than these, NAD(P)independent dehydrogenases including flavoproteins, quinoproteins, and metalloproteins utilize not NAD(P) but other redox compounds including redox proteins.
NAD(P)-independent dehydrogenases catalyze the transfer of electron and/or hydride
ion. NAD(P)-reducing dehydrogenases (e.g. NAD(P)-reducing hydrogenase (H 2 ase)
and NAD(P)-linked molybdenum (Mo)- (or tungsten (W)-)containing formate dehydrogenase (FoDH)) utilize NAD(P)
+ as an electron acceptor, but NAD(P)
+ can be
replaced with other oxidizing compounds with electron-transfer property, because
they have a flavin-containing diaphorase subunit that can catalyze both electron
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
K. Kano et al., Enzymatic Bioelectrocatalysis,
https://doi.org/10.1007/978-981-15-8960-7_1
1