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    Biochemical activity of Malate dehydrogenase

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    The following questions refer to the mitochondrial enzyme MALATE DEHYDROGENASE.

    What is the chemical reaction, within the citric acid cycle, that is catalyzed by malate dehydrogenase, and which substrates, products, and/or cofactors are involved?

    The reaction from the previous question is classified as a dehydrogenation, which means that the reaction represents a(n) _______________ wherein ________________.

    a. oxidation reaction; malate loses electron(s)
    b. oxidation reaction; malate gains electron(s)
    c. reduction reaction; malate loses electron(s)
    d. reduction reaction; malate gains electron(s)
    e. hydrolysis reaction; malate loses hydrogen(s)

    The ΔG'° for the chemical reaction catalyzed by malate dehydrogenase is +29.7 kJ/mol. Under standard biochemical conditions, is this reaction exergonic, endergonic, or close to equilibrium? Under these conditions, in which direction would this chemical reaction be expected to proceed?

    Under typical cellular conditions of glycolysis and the citric acid cycle, does the malate dehydrogenase reaction represent a reversible catalytic step or an essentially irreversible step? Based on this answer, is the actual ΔG expected to be greater than, less than, or about equal to the ΔG'°? Why?

    Within the context of the citric acid cycle the dehydrogenation of malate proceeds to the right (i.e. formation of oxaloacetate is favored). Why is this is so, and what other reactions or substrates/products of the TCA cycle are important here?

    When gluconeogenesis is favored (and glycolysis is downregulated), describe the chemical reaction that is catalyzed by malate dehydrogenase. Under such conditions, is the formation of oxaloacetate or malate favored? Explain why the reaction proceeds in the direction you describe.

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    Solution Summary

    Malate dehydrogenase is a key enzyme of kreb cycle. It catalyzes the formation of NADH2. In malate shuttle, on other hand, extramitochondrial NADH is oxidized by OAA by the action of the cytoplasmic malate dehydrogenase to yield malate. It enters into the mitochondria via malate - succinate carrier and is oxidized to OAA by the action of the action of the intramitochondrail malate dehydrogenase. Here malate shuttle is reversible reaction and can function in either direction