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J. A. Elegbede and A. Lateef
AuNPs biosynthesis. Nitrate reductase is an attractive enzyme that mediates the translation of nitrate to nitrite in the nitrogen cycle by the appropriate microbial enzymes
(Moteshafi et al. 2012). It is as well a multidomain enzyme having the combination
of the prosthetic groups; Fe-heme, molybdopterin and flavin adenine dinucleotide
(FAD) in a 1:1:1 stoichiometry which facilitates shift of electron from NAD(P)H to
nitrate. In fungi, extracellular biosynthesis of nanoparticles has been said to be the
outcome of nitrate reductase through bioreduction of metal ions (Ingle et al. 2008).
It was also emphasized that NADH-dependent reductases play important function in
the reduction of gold chloride salt in fungi (Rai et al. 2009).
Studies have elucidated the active participation of nitrate reductase in the biosynthesis of metallic nanoparticles extracellularly (Kumar et al. 2007). Commercially
available nitrate reductase disks have revealed that NADH-reliant reductases were
implicated in the bioreduction of Ag
+ ions to Ag
0 and thus formation of AgNPs
(Ingle et al. 2008). It was reported by Senapati et al. (2005) that Fusarium oxysporum
produced extracellular reductases which caused the bioreduction of Au
3+ and Ag
+
to Au–Ag alloy NPs. In another study, nitrate reductase obtained from F. oxysporum
was in addition applied in a condition free of oxygen in the presence of NADPH,
phytochelatin (stabilizer protein) and 4-hydroxyquinoline (electron carrier) for the
biosynthesis of AgNPs (Karbasian et al. 2008). Penicillium brevicompactum was also
described to release NADH-reliant enzyme nitrate reductases which caused the bioreduction of Ag
+ ions (Shaligram et al. 2009). Moreover, several fungi have produced
some extracellular enzymes for instance acetyl xylan esterase, cellobiohydrolase, Dglucosidase cellulose, xylanase, laccase, keratinase, peroxidases, proteases, reductases and fibrinolytic enzyme (URAK) which have been known to take a key function
in the eco-friendly synthesis of metallic nanoparticles (Deepak et al. 2011; GholamiShabani et al. 2015; El-Batal et al. 2015; Lateef and Adeeyo 2015; Lateef et al.
2015a; Elegbede et al. 2018, 2019, 2020; Wadhwani et al. 2018). Reports have also
revealed that protein moieties from these enzymes are mostly accountable for ecofriendly synthesis of nanoparticles where they could be functioning as non-enzymatic
catalytic reaction. Durán et al. (2015) described the contribution of disulfide bridge
moieties and thiol groups of enzymes as the reaction sites of nanoparticles formation
in a review article. The disulfide and thiols protein moieties were proposed as the
likely catalytic site for most chemical oxido-reductions resulting in metallic nanoparticles biosynthesis. Correspondingly, the S–H and S–S moieties of enzymes which
have been denatured could reduce metallic ions to nanoparticles.
2.5 Some Enzyme-Mediated Biosynthesized Nanomaterials
2.5.1 Silver Nanoparticles (AgNPs)
Silver nanoparticles are at present commercially available as antimicrobial agents
used in places such as railway stations, elevators etc. across the world. They are moreover employed as antimicrobial substances implanted in surgical catheters so as to
J. A. Elegbede and A. Lateef
AuNPs biosynthesis. Nitrate reductase is an attractive enzyme that mediates the translation of nitrate to nitrite in the nitrogen cycle by the appropriate microbial enzymes
(Moteshafi et al. 2012). It is as well a multidomain enzyme having the combination
of the prosthetic groups; Fe-heme, molybdopterin and flavin adenine dinucleotide
(FAD) in a 1:1:1 stoichiometry which facilitates shift of electron from NAD(P)H to
nitrate. In fungi, extracellular biosynthesis of nanoparticles has been said to be the
outcome of nitrate reductase through bioreduction of metal ions (Ingle et al. 2008).
It was also emphasized that NADH-dependent reductases play important function in
the reduction of gold chloride salt in fungi (Rai et al. 2009).
Studies have elucidated the active participation of nitrate reductase in the biosynthesis of metallic nanoparticles extracellularly (Kumar et al. 2007). Commercially
available nitrate reductase disks have revealed that NADH-reliant reductases were
implicated in the bioreduction of Ag
+ ions to Ag
0 and thus formation of AgNPs
(Ingle et al. 2008). It was reported by Senapati et al. (2005) that Fusarium oxysporum
produced extracellular reductases which caused the bioreduction of Au
3+ and Ag
+
to Au–Ag alloy NPs. In another study, nitrate reductase obtained from F. oxysporum
was in addition applied in a condition free of oxygen in the presence of NADPH,
phytochelatin (stabilizer protein) and 4-hydroxyquinoline (electron carrier) for the
biosynthesis of AgNPs (Karbasian et al. 2008). Penicillium brevicompactum was also
described to release NADH-reliant enzyme nitrate reductases which caused the bioreduction of Ag
+ ions (Shaligram et al. 2009). Moreover, several fungi have produced
some extracellular enzymes for instance acetyl xylan esterase, cellobiohydrolase, Dglucosidase cellulose, xylanase, laccase, keratinase, peroxidases, proteases, reductases and fibrinolytic enzyme (URAK) which have been known to take a key function
in the eco-friendly synthesis of metallic nanoparticles (Deepak et al. 2011; GholamiShabani et al. 2015; El-Batal et al. 2015; Lateef and Adeeyo 2015; Lateef et al.
2015a; Elegbede et al. 2018, 2019, 2020; Wadhwani et al. 2018). Reports have also
revealed that protein moieties from these enzymes are mostly accountable for ecofriendly synthesis of nanoparticles where they could be functioning as non-enzymatic
catalytic reaction. Durán et al. (2015) described the contribution of disulfide bridge
moieties and thiol groups of enzymes as the reaction sites of nanoparticles formation
in a review article. The disulfide and thiols protein moieties were proposed as the
likely catalytic site for most chemical oxido-reductions resulting in metallic nanoparticles biosynthesis. Correspondingly, the S–H and S–S moieties of enzymes which
have been denatured could reduce metallic ions to nanoparticles.
2.5 Some Enzyme-Mediated Biosynthesized Nanomaterials
2.5.1 Silver Nanoparticles (AgNPs)
Silver nanoparticles are at present commercially available as antimicrobial agents
used in places such as railway stations, elevators etc. across the world. They are moreover employed as antimicrobial substances implanted in surgical catheters so as to