Ethanol oxidation reaction by alcohol dehydrogenase (ADH) (EC 1.1.1.1) enzyme in catalytic domain with nicotinamide adenine dinucleotide NAD⁺ oxidized form NAD⁺ and zinc Zn²⁺ ion coordinated alcohol group and His51 hydrogen bond linked water molecule.
H₃C-CH₂-OH+NAD⁺+H₂OH₃C-HC=O+NADH+H₃O⁺ ; E°= -0.113 V;


hydride H^- ion tuneling from reduced form substrate ethanol H₃C-CH₂-OH in one attempt to oxidised form NAD⁺froming reduced form of NADH
in second instant process jump of proton H⁺ to water molecule H₂O coordinated by zinc Zn²⁺ ion to form hydroxonium ion H₃O⁺.
    ADH during alcohol oxidation in water medium driven by catalytic zinc Zn²⁺ site moiety coordinated alcohol group -CH2-O-H as acid dissociates proton =>H⁺ which jump via two amino acids Brønsted basis like as relay assistants Ser-48, His-51, to H₂O water molecule forming hydroxonium ion H₃O⁺:


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