five known families of carbonic anhydrases (a, b, g, d and z) that catalyze the
ID: 536101 • Letter: F
Question
five known families of carbonic anhydrases (a, b, g, d and z) that catalyze the reaction,
CO2 + H2O <-> HCO3- + H+
a-Carbonic anhydrase is found in humans and all other animals. b-Carbonic anhydrase is found in higher plants and certain bacteria. Unlike the a form, the b form is an allosteric enzyme that is regulated by a bicarbonate ion (also a product of the reaction). Given this information, complete the following questions.
Both a- and b-carbonic anhydrases follow a ping-pong mechanism in which the first substrate bound by the enzyme is CO2. In what order are the other molecules in the reaction (H2O, HCO3-, H+) bound or released by the enzyme?
Explanation / Answer
The mechanism proposed looks like this
EZnOH- (enzyme) + CO2 <---------> EZn(OH-) CO2
EZn(OH-) CO2 <--------> EZnHCO3-
EZnHCO3- <---------> EZnH2O + HCO3-
So HCO3- is the first one to be released
Later EZnH2O reacts with buffer solution to give H+ proton
The order in which molecules are released :
1. HCO3- 2. H+ 3. H2O (left out)
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