Key to Exercise on Enzyme Regulation
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Key for Exercise on Enzyme Regulation

1.

Table 1: Regulation of Enzyme Activity

type of regulation

proteolysis

covalent modification

allosteric regulation

Is it reversible?

N

Y

Y

Is another enzyme required?

Y

Y

N

Can it involve activation only, inhibition only, or both?

activation
only

both

both

Can amplification occur?

Y

Y

N

2.

a.

Table 2: Classifying the Molecules that Bind PFK-1

fructose-6-P

ATP

fructose-2,6-bis-P

AMP

Active site (C),
allosteric site (L), or both (B)?

C

B

L

L

Substrate (S), modulator (M), or both (B)?

S

B

M

M

Conformation stabilized
(R or T)?

R

T

R

R

Converted to product (P) or unchanged (U)?

P

P/U

U

U

b. ATP is a co-substrate coenzyme that is a negative modulator. When ATP binds in the active site, it can be converted to product. When ATP binds in an allosteric site, it is not changed by PFK-1; instead, it stabilizes the T conformation of PFK-1.

3. a. K0.5 is the substrate concentration required for the enzyme rate to be half of Vmax.
    Kd is the dissociation constant that indicates the affinity of a ligand for a protein to
    which it binds.

     b. No          c. Probably not

4. a.

                               

                     ATP                                                                     AMP               

                                           

       fructose-2,6-bis-P                                                       fructose-6-P        

     b. ATP and AMP probably would because they're very similar.


     c. There are many possible correct answers for this. Hydrophobic interactions are
          very unlikely, but both hydrogen bonds and ionic interactions can easily occur.

5. a-b.

c. For a, K0.5 is about 3; for b, K0.5 is 2, and for c, K0.5 is nearly 5.

6. a. Citrate3- could have an ionic interaction with either of the circled side chains.
            Since that might disrupt a different ionic interaction, it could stabilize a different
            protein conformation. When citrate3- leaves, however, the first conformation
            would form again.
b. Protein kinase A would transfer a phosphate from ATP to the serine side chain
            in the rectangle, which would change a polar uncharged group to one with a
            negative charge. That would probably be attracted to the arginine side chains
            and cause a conformation change.
            Removal of the phosphate by a phosphatase (adds H2O to the phosphate ester
            bond) would restore the original conformation.
c. Trypsin hydrolyzes the peptide bond on the carboxyl side of arginine side chains,
            so two potential sites of action are indicated by the two ovals. This would cut the
            protein chain into two parts, which would change its conformation and function.
            This change can not be reversed.

 

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