Homework answers / question archive / Chem 4343 Chapter 11, Kinetics & Enzyme Regulation, pp #2 1

Chem 4343 Chapter 11, Kinetics & Enzyme Regulation, pp #2 1

Biology

Share With

Chem 4343
Chapter 11, Kinetics & Enzyme Regulation, pp #2
1. Sulfite oxidase is an enzyme that catalyzes the following reaction
S037 + 2 cytochrome C,,iqizeg t+ H,O — SO 7 + 2 cytochrome C, duced + 2 Ht
Kinetic constants for the normal (wild type) form of the enzyme along with two mutant
forms of the enzyme were studied. The R (arginine) residue at position 160 in the
polypeptide chain is thought to be situated in the active site of the enzyme. In the mutant
designated R160Q, the R (arginine) at position 160 in the polypeptide has been replaced
by Q (glutamine). In the mutant designated R160K, the R (arginine) at position 160 in
the polypeptide has been replaced by K (lysine). In these studies the substrate for sulfite
oxidase was sulfite (SO37°).
Enzyme Km (uM) Keat (sec”!) Koat/Kimn (10° M7! sec")
Wild-type 17 18 1.1
R160Q 1900 3 0.0016
R160K 360 5.5 0.015
a. Is arginine (R) an amino acid that is essential to the active site of sulfite oxidase?
Based on the data above and your knowledge of enzyme-substrate interactions, explain
your rationale.
b. Explain why R160K exhibits properties that are intermediate between wild type and
the R160Q mutant.
c. Based on the data, which enzyme form exhibits the highest efficiency. Explain your
rationale.

2. Explain why a competitive inhibitor affects Km differently than an uncompetitive
inhibitor. In your explanation please include a discussion of rate constants and how this
ties to the impact on Km.

4. A biochemist is studying the interaction of three substrates (labeled substrate A,
substrate B, and substrate C) with an enzyme.
(a). Design an experiment to help the biochemist determine which substrate is
preferentially bound by the enzyme (ie the enzyme has the highest affinity for binding
this substrate). Include variables held constant and those that would change as you are
conducting the experiment. Include an explanation of how the results would be analyzed
to determine enzyme preference (ie now that you have the data from the lab, what do you
do with it to determine which substrate is preferentially bound). Please be specific.

(b) Design an experiment to help the biochemist determine the highest turnover number
(ie kcat) when comparing the 3 substrates. Include variables held constant and those that
would change as you are conducting the experiment. Include an explanation of how the
data would be analyzed to determine highest turnover number. Please be specific.

5. A graduate student is studying an enzyme found in the rare spotted turkey.
Results indicate the wild type protein is a 80 kilodalton monomer and exhibits
activity. The student is also studying a mutant form of the enzyme that is inactive
(exhibits no enzymatic activity) and has a molecular weight of 90 kilodaltons.
Genetic analysis indicates that the gene coding for the mutant protein differs from
the gene coding for the normal protein by only one base (ie a guanine substituted
for a cytosine). Explain these results.