Question

D-Xylulose, one of the intermediates of the Calvin Cycle, can be converted to D-xylose, or "wood sugar" in a single enzymatic step. Propose a name for the enzyme that carries out the reaction and draw the reaction mechanism. D-Xylose, or "wood sugar" can act as a carbon source for many kinds of bacteria, including Caulobacter crescentus. Recently, the xylose dehydrogenase (XDH) gene was discovered in C. crescentus, and the xylose metabolic pathway was proposed to involved a gamma-lactone intermediate. Propose a mechanism for the XDH enzyme, which also uses NADP* as a substrate.

Answer 1

8)

The synthesis of Xylulose-5-P form xylose is as follows:

он он Xvlose-Reductase Ho но он он он NADPH он Xylose Xylitol Xylitol-Dehydrogenase Pentosephosphate-Pathway NAD+ OH Xylulokinase но он он он ATP Xylulose-5-P Xylulose

Since, the Xylulose and xylose are isomers, so the enzyme xylose isomerase (direct pathway) or xylitol dehydrogenase and xylose reductase (an indirect pathway) convert the Xylulose-5-P to xylose-5-P.

9)

The reaction catalyzed by the xylose dehydrogenase (oxidoreductases) is as follows:

D-xylose + NAD⁺D-xylonolactone + NADH + H⁺

The mechanism of xylose dehydrogenase is similar to oxidoreductases.