Zinc/CA/CPA

Question 1

What are the different zinc metalloenzymes? What is their function?

Answer 1

zinc finger proteins
- act as gene switches = bind to DNA to turn RNA production on/off

superoxide dismutase
- catalyse the disproportionation of toxic superoxide anion to oxygen and peroxide

zinc and insulin
- allows the slow release of insulin as proinsulin (precursor) has a zinc centre

Question 2

What are the properties zinc?

Answer 2

zinc is a good Lewis acid

zinc has no preference for octahedral or tetrahedral geometry

zinc is more suitable than cobalt as it has only one stable oxidation state

zinc does not readily hydrolyse at physiological pH

Question 3

What are the two ways in which zinc can act?

Answer 3

can directly interact with nucleophilic substrates
- polarises the carbonyl bond

activates water
- ionises bound water (formation of lewis basic species = ZnOH)

Question 4

What is carbonic anhydrase?

Answer 4

an enzyme which catalyses the reaction of hydrolysis of carbon dioxide and water to bicarbonate and hydrogen ions

Question 5

What is the structure of carbonic anhydrase?

Answer 5

has a zinc centre

• 3 histidines residues are attached
• 1 water molecule is attached = is hydrolysed at physiological

tetrahedral coordination

Question 6

What is carboxypeptidase A (CPA/CBP-A)?

Answer 6

an enzymes which catalyses the hydrolysis of C-terminal amino acids from the polypeptide chains

Question 7

What is the structure of carboxypeptidase A?

Answer 7

has a zinc centre

• 2 histidine residues are attached
• 1 water molecule is attached
• 1 glutamate molecule is attached = bidenate ligand

pentacoordinated