1. Brief identification (1.5pts each)

    The kind of enzyme inhibition that can overcome by a sufficiently high concentration of the enzyme's substrate -->?

    The molecule that binds to Zn ion, and is thereby activated for attack on the carbon atom of CO2, in the active site of carbonic anhydrase --> ?

    Two chemical species (molecules, atoms, or ions) that stabilize the T-state of hemoglobin -->??

    The characteristic of the specificity pocket of elastase that is largely responsible for the enzyme's specificity for cleavage at Ala or Gly -->?

    Any of the other classes of protease, besides Ser protease -->?

    The amino acid whoes side-chain links to the peptide backbone in two places, restricting the torsion angle phi

    An aromatic amino acid whose side-chain includes ahydroxyl group

2. The Michaelis-menten equation is
                    V= Vmax[S]/Km+[S]

    Km is the Michaelis constant, given by

                    Km = k-1 + k2/k1

    The Michaelis-Menten equation is based on a simple sheme that desribes enzym-substrate interaction, catalysis, and product release

 A. (4 points) Write down this simple reaction scheme, and use it to define the constants k1, k-1, and k2

 B. (6 points) Draw the V (velocity) vs. [S] curve for an enzyme that follows the Michaelis-Menten equation. Indicate on the gragh the values of Vmax and km. What is the sigmificance of Km for the function of an enzyme?

3. A (9 pts) Shetch the catalytic triad that occurs in the active site of chymotrypsin. What role is each the three residues believed to play in the catalysis of peptide-bond hydrolysis? Illustrate by means of simple sketch of the early events in peptide hydrolysis (substrate binding, and initial attack step).

   B(6 pts) Enzymes are effetive catalysts largely because they utilize a number of different "tactics" to promote the reaction. List three different tactics that chymotrypsin uses to accelerate peptide-bond hydrolysis

   C(9 pts) Sketch the acyl-enzyme intermediate at the chymotrypsin active site, then sketch the each steps immediately following, up to and including removal of the acyl group from the enzyme.

4. A. (4 pts) Name two mechanisms that cells use to regulate enzyme activity other than allosteric regulation. Illustrate each with a simple sketch.

    B. (8 pts) Aspartate transcarbamoylase provides a well-understood example of allosteric regulation. What are the key features of regulation of this enzyme? Explain using a simple sketch. What are the key features of different states of the enzyme? What allosteric effector is involved?

    C. (6 pts) Sketch the kinetic behavior! (Velocity vs. substrate concentration) for ATCase, in the presence and absence of the allosteric effector (assume that the effector is at saturating concentrations when present). Clearly label the curves on your sketch.

5. (18 pts) Identify (1.5 pts each)

   1) This glycolytic enzyme is not used in gluconeogenesis, but is bypassed in a metabolic step catalyzed by fructose 1, 6 bisphosphatase.

   2) This interdediate in gluconeogenesis is the only metabolite that is not also an intermediate in glycolysis.

   3) This enzyme of gluconeogenesis is found inside the mitochondrion

   4) This enzyme of gluconeogenesis is lovated at the endoplasmic reticulum membrane.

   5) In the synthesis of glycogen from glucose1-phosphate, a molecule of this high-energy triphosphate is consumed for each glucose unit incorporated into glycogen.

   6) The most common chemical linkage in glycogen between glucose unit.

   7) Binding of this allosteric effector to phosphorylase causes a conformational change that allows bound protein phosphatase 1 to dephosphorylate phosphorylase.

   8)-9). This two enzymes, found in the same protein and import!ant for reciprocal regulation of glycolysis and gluconeogenesis, are known collectively as the "tendem enzyme"

   10)-11) When insulin is circulating in the blood, the plasma membrane level of glucose-transporter-4 (GLUT4) greatly increases in these two tissues

   12) This "second messenger enzyme" uses ATP as a substrate, and is directly stimulated by the a subunit of a G-protein bound to GTP, if either glucagon or epinephrine bind their receptors.

6. (17 pts)

   A. Circle all correct answers. When insulin levels in the blood are high, we expect that:

     a) cAMP levels in skeletal muscl are high

     b) glucagon level in the blood are high

     c) phosphorylase kinase would be dephosphorylated

     d) skeletal muscl glycogen synthase activity would be high

     e) liver glycogen phosphorylase activity would be high

      f) protein phosphatase 1 would be dissociated from phosphorylase in the liver

  B. Briefly describe the biochemical specializations that allow the liver to consume and metabolize much more glucose than other tissues when blood glucose levels are high. In one sentence, describe what happens to the glucose taken up by the liver under these conditions.

  C. If cAMP levels are high in skeletal muscle, both glycogen breakdown and glycolysis are stimulated. If cAMP levels are high in a liver cell, glycogen breakdown is stimulated, but glycolysis is inhibited. Although we have not discussed this in class, speculate on possible differences between muscle and liver that would explain how glycolysis can be stimulated in muscle by high cAMP (not inhibited as in the liver).

7. (8 bonus points) Liver cells can synthesize glucose from succinate through pathway that we have studied in class.

  A. Whrite a single, balanced net reaction that summarizes the overall reaction for the biosynthesis of glucose from succinate (show net consumption or production of triphosphates, and other cofactors)

  B. Write tow balanced half reactions that illustrate the overall electron donor and electron acceptor half cells for the conversion of succinate to glucose