MBB 222 Study Guide - Final Guide: Oxyanion Hole, Tetrahedral Carbonyl Addition Compound, Protoporphyrin Ix
11 Dec 2016
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Mbb222 final exam review: chymotrypsin mechanism and hemoglobin. Chymotrypsin starts as a free enzyme with an active site, oxyanion hole and a hydrophobic pocket. Oxyanion hole helps stabilize short-lived tetrahedral intermediates and is composed of glycine and serine residues. Step 1: a substrate binds to chymotrypsin and forms the enzyme-substrate complex. The side chain of the residue adjacent to the peptide bond to be cleaved fits into the hydrophobic pocket in the enzyme and is positioned for the peptide bond to be attacked. Step 2: the his and ser residues interact, causing the formation of a strongly nucleophilic alkoxide ion on the ser residue. Ser then attacks the carbonyl on the peptide group and forms a tetrahedral acyl-enzyme intermediate that is short-lived. There is a short-lived negative charge on the carbonyl oxygen in the substrate that is stabilized by h-bonding in the oxyanion hole.
