BCHM 463 Supplemental Problem Set #1 2005

1. Write the net reaction of glycolysis.

+ + Glucose+ 2 ADP ++2 NAD + 2 Pi 2 Pyruvate 2 ATP+ 2 NADH + 4 H + 2 H2O

2. During glycolysis, how many ADP molecules are converted to ATP. Explain this answer with regard to your answer to #1.

4 ADP molecules are converted into ATP. There is a net gain of only 2 ATP molecules because 2 are consumed during the first stage of glycolysis.

3. What are the three metabolically irreversible steps of glycolysis? What general type of reaction is catalyzed by these enzymes? Why are these reactions irreversible?

Glucose phosphorylation catalyzed by hexokinase; fructose-6-phosphate phosphorylation catalyzed by phosphofructokinase; and phosphoryl transfer from PEP to ADP catalyzed by pyruvate kinase

All three reactions involve group transfer reactions.

The reactions are irreversible because they have a large negative ∆G. Note: ∆G should not be confused with ∆G°´. See Table 14.1 for more information.

4. The following is an intermediate formed along the glycolysis pathway. This is produced and consumed by which enzymes? Provide the net reaction for each catalytic process.

O OH -2 O3PO OH HO OH -2 OPO3 phosphoglucose OH phosphofructose OPO -2 isomerase O kinase O 3 O -2 -2 HO O3PO OH O3PO OH HO OH OH OH HO HO OH

PGI G6P F6P

PFK F6P+++ ATP FBP ADP H+ Mg2+

5. Name the compounds that serve as phosphoryl group donors in glycolysis and also name the enzymes that catalyze these phosphoryl transfer steps.

ATP 1,3-BPG hexokinase phosphoglycerate Glucose G6P kinase 1,3-BPG 3PG phosphofructose kinase F6P FBP ADP ATP

PEP Pi GAPDH pyruvate GAP 1,3-BPG kinase PEP Pyruvate

ADP ATP BCHM 463 Supplemental Problem Set #1 2005

6. Phosphoglycerate mutase catalyzes the conversion of 3-phosphoglycerate to 2-phosphoglycerate. 2,3- Bisphosphoglycerate (2,3-BPG) is formed as an intermediate. Describe the catalytic process that forms and consumes this intermediate. Does 2,3-BPG serve any physiological function?

3PG 2,3-BPG 2PG

Each step represents group transfer. First, a phosphoryl group is transferred from the enzyme to the substrate to generate the bisphospho intermediate. This is followed by transfer of the second phosphoryl group back to the enzyme.

Recall that 2,3-BPG is an allosteric modulator of hemoglobin in erythrocytes although the 2,3-BPG produced by escape from phosphoglycerate mutase is neglible. This of course means that there is some other source of 2,3-BPG in erythrocytes.

7. When lactate is converted to pyruvate, which of the following, if any, are true? a. NAD+ is converted to NADH b. ADP is converted to ATP c. NADH is converted to NAD+ d. ATP is converted to ADP e. FAD is converted to FADH

A is the only answer that is true. Remember that the reaction catalyzed by lactate dehyrogenase is freely reversible.

8. In Greek mythology, the Three Fates, or Moirae, were the goddesses who controlled the destiny of everyone from the time they were born to the time they died. Pyruvate also has three fates: fill in the boxes below to indicate the fate of pyruvate produced during glycolysis. Glucose

Glycolysis

Pyruvate

anaerobic anaerobic conditions conditions aerobic conditions

2 EtOH + 2CO 2 Lactate 2 CO2

2 AcetylCoA

citric acid cycle

4 CO2 + 4 H2O

9. Which enzymes in glycolysis utilize covalent catalysis during conversion of substrate into product? Write the enzyme names and the net reaction catalyzed by each. BCHM 463 Supplemental Problem Set #1 2005

GAPDH

+ GAP + Pi +++NAD+ 1,3-BPG NADH H

-2 O OPO3 Enz S OH acylenzyme intermediate

Also, phosphoglycerate mutase see # 6, above

10. Glycolysis is regulated by controlling which enzymes? Identify the mechanisms of control for each. (e.g. product inhibition or feedback inhibition)

Hexokinase: product inhibition by Glc6P Posphofructokinase: ATP is an allosteric inhibitor; AMP, ADP, F-2,6-bisP, and other compounds overcome this inhibition and therefore serve as activators Pyruvate kinase: product inhibition by ATP (allosteric); FBP acts as an allosteric activator

11. The pentose, xylose, has the same structure as the hexose, glucose, except that it has a hydrogen atom at C-5 in place of a hydroxymethyl group. However, xylose still stimulates hydrolysis hexokinase- dependent hydrolysis of ATP. Why?

Although xylose CANNOT serve as a substrate for hexokinase, it can bind to the enzyme and induce a conformation similar to that induced by glucose and necessary for enzymatic activity. .