hw 2 - Problem Set #2 Cofactors 1. Serotonin is...

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Unformatted text preview: Problem Set #2 Cofactors 1. Serotonin is biosynthesized from the amino acid L-tryptophan. Following oxidation at the 5 position of the indole ring by tryptophan hydroxylase, serotonin is generated with the assistance of the pyridoxal-phosphate cofactor. Provide a reasonable mechanism for the following transformation. HO O OH HN HO O OH HN NH2 HN HN HO HO O P O O N H OP O3 HO PLP NH2 HN NH2 HO HO O O H HN B R H B R HN HO N H OP O3 O HO N H H HO HO HN HN NH2 N H H2N HO OH OPO3 HO H O H2 HN HN HO N H OP O3 2. Fumaric acid is formed oxidatively with the assistance of an enzyme cofactor. Of the cofactors reviewed in lecture, which is the most likely candidate for this conversion? Provide a reasonable mechanism for the following transformation using the cofactor that you have chosen. O HO OH O HO O O OH B O HO HH O HO O N N R N NH O N R O HH OH O OH + FADH2 O HO HH O O HH B OH O HO O NH2 OH + NADH H 3. In week 2’s assigned reading (Walsh et al.), the authors describe the catalytic activity of the rebF/rebH two ­component reductase/halogenase. They observed that in the presence of an air ­saturated solution, the reaction rate decreases significantly. Explain this observation. RebF and rebH act as a flavin reductase and FADH2 ­dependent halogenase, respectively. The activity of rebH depends on the conversion of FADH2 to FAD in order to selectively generate 7 ­chlorotryptophan. In the presence of an air ­ saturated solution, molecular oxygen (O2) acts as an oxidant to oxidize FADH2 back to FAD limiting “the availiability of the reduced cofactor for diffusion into and binding in the halogenase active site”. 4. As mentioned in lecture, what is nature’s equivalent to LiAlH4? NADH ...
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