8B: Oxidative Enzymes
- Page ID
- 4607
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Learning Objectives
- state the type of oxidizing reagent used and the products forms on oxidation reactions catalyzed by dehydrogenases, monoxygenases (hydroxylases), dioxygenases, and oxidases;
- draw the reactive end of NAD+ and mechanisms showing it's reactions with substrates in enzyme-catalyzed two electron oxidation reactions;
- explain differences in chemical reactivity of NAD+ and FAD in one and two electrons oxidations and with dioxygen;
- describe the stereochemistry of the alcohol dehydrogenase-catalyzed oxidation of prochiral ethanol by NAD+;
- explain why FAD/FADH2 are often tightly bound to dehydrogenases in contrast to NAD+/NADH where are freely diffusable substrates;
- given standard reduction potentials, determine the ΔGo' for given redox reactions;
- explain why different FAD and other flavin containing dehydrogenases have varying standard reduction potentials for the flavin but NAD+ dependent dehydrogenase have only one;
- describe the role of heme in mono- and dioxygenases in activating dioxygen and minimizing side reactions of ROSs;
- describe the biological role of cytochrome P450s;
- define and give examples of oxidases;
- compare the contrast the role of the heme in carrying hemoglobin and myoglobin, monoxygenases, and in oxidases.
- B1. General Oxidizing Agents
- Oxidizing agents are required to oxidize organic molecules. In organic lab, you never used dioxygen as an oxidizing agent. It is difficult to limit the extent of oxidation using dioxygen. In addition, side reactions are likely given the nature of the reactive oxygen reduction products.
- B2. The Chemistry of NAD+ and FAD
- NAD+ is a derivative of nicotinic acid or nicotinamide.
- B8. Oxidases
- Oxidase enzymes does not incorporate dioxygen into an organic substrate. Rather it accepts electrons released from an organic substrate, through intemediate electron carriers (such as ubiquinone and cytochrome C) to form superoxide (as in NADPH-oxidase), hydrogen peroxide (as in xanthine oxidase) or water (as in cytochrome C oxidase). The mechanism of cytochrome C oxidase again supports our expectations about enzymes that use dioxygen.