CHM 4139 Lecture Notes - Lecture 17: Lactose Intolerance, Corn Stover, Sitagliptin

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Chm 4139- lecture 17: determination of enzyme mechanism (cont"d: x-ray crystallography. Crystal structure of enzyme with unreactive analogue of dmapp and trp bound at active site was solved [fig 7] here. Binding mode of dmapp analogue and trp is consistent with sn1 mechanism. The potential catalytic residues were identified to be k174 and e89 (acid base catalyst, not confirmed: mutagenesis. Glycine is not usually use as it can potential distort the secondary structure. Alanine is usually use as it has a small alkene side chain that is unreactive. E89a: devoid of activity, strongly suggest that e89 is a general acid/base catalyst that deprotonates and reprotonates trp nitrogen side-chain. K174a: 95% decrease in activity, loss of function. Hypothesis: a base is needed to deprotonate the arenium intermediate. But even a weak base such as glu can deprotonate the arenium give its low pka. Outlook: ph profile to match k+e as general acid/base catalyst.

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