Biochemistry 3381A Study Guide - Midterm Guide: Carbonic Anhydrase, Schiff Base, Ribonuclease
27 Dec 2013
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Resting state of enzyme: 2 histidines involved; one acting as acid, one acting as a base. This lys has to be in an environment that decreases pka, to be neutral. Glu oh should be anion @ ph 7 but enzyme has formed microenvironment to cause it to be in protonated form. Asp o- negatively charged like we would normally expect. Substrate is peptide and it also uses h2o. His prefers to be +ve (pka = 8) pka of ser decreases b/c +ve. Covalent b/c ser attacks and is covalently bound to peptide. Basic his attacks the 2" oh and the acidic his breaks the phosphodiester. *his can act as a or b depending on microenvironment. Carbon dioxide comes in, oh attacks then attaches and becomes bicarbonate. Zn stabilizes oh- @ start of rxn and favors formation of bicarbonate (hco3-) Water deprotonated by proton relay with the histidines; until.
