Many enzymes are inhibited irreversibly by heavy metal ions such as Hg2, Cu, or

Question

Many enzymes are inhibited irreversibly by heavy metal ions such as Hg2, Cu, or Ag*, which can react with essential sulfhydryl groups to form mercaptides Enz-SH Ag+ ? H+ + Enz-S-Ag + The affinity of Ag' for sulfhydryl groups is so great that Ag can be used to titrate-SH groups quantitatively. To 10.0 mL of a solution containing 1.7 mg/mL of a pure enzyme, an investigator added just enough AgNO3 to completely inactivate the enzyme. A total of 0.384 umol of AgNO3 was required. Calculate the minimum molecular weight (M.) of the enzyme. Number minimum M The M you determined above was not exact, but was a minimum value for the M of the enzyme. Why does the M, value obtained this way give only the minimum molecular weight? O O O O The Ag' would also react with the terminal carboxyl group. There is only one titratable -SH group per protein molecule. There are no disulfide bonds in the protein. There is only one polypeptide chain. O Previous Give Up & View Solution O check Answer Next ?? Exit Hint about us careers privacy policy terms of use co

Explanation / Answer

1) given that the solution contain 1.7mg/ml of enzyme. Thus, 10 mLof solution contain = 17mg of enzyme

given that, total AgNO3 required =0.384 u mol But it has to be converted in mMol .Thus 0.384*10-3 is required to titrate the 17mg of enzyme.

If an equllibrium exist then

0.384*10-3 = total enzyme (mg)/ mr (mg/mol)

minimum molecular weight (mr) = 1.7*10 /0.384*10-3

= 4.427*10-4 = 44,270

Value obtained in this way give only the mr because the calculation assume that there is only one titrable -SH group per protein molecule.

2) Characteristic of allosteric enzymes are:

Do not follow hyperbolic curve but the 'S' sigmoid curve because binding is cooperative.

3) Calalytic triad of serine protease enzymes have preserved amino acid which is located in the active site of the enzyme where catalysis occurs and the coordinated structure of triad consists of three amino acids namly:

Histidine , Serine and aspartate.

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