PH regulation of PFK enzyme and rate of glycolysis: Why does lower ph regulation (which has a high amount of acid) inhibit pfk, and a higher ph (less acidic and more basic) is a stimulator of pfk enzyme and rat of glycolysis?

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Sixta KovacekLv2

28 Sep 2019

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Case Study Section 2 â glycolysis
Based on âMonday at the Metabolic Clinic, Adventures in Glycolysisâ by Nancy Boury (National Center for Case Study Teaching in Science)

Background:
You have been chosen for a very competitive undergraduate clinical internship at St. Visintainerâs Hospital and Metabolic Clinic working with Dr. Saccharo, an expert in enzyme deficiency disorders related to glycolysis. Before your first day Dr. Saccharo has asked that you review the reactions of glycolysis and the concept of isoenzymes.

Recall that isoenzymes are groups of enzymes that catalyze the same reaction in that they use the same reactants to product the same products. They may have different genes, tissue expression, developmental timing of expression, and affinities for their substrates. As an example, phosphofructokinase-1 has 3 isoenzyme forms: PFK-L is expressed in the liver and the gene is found on chromosome 21; PFK-M is expressed in the muscle and the gene is found on chromosome 12; and PFK-P is expressed in platelets and the gene is found on chromosome 10.

Question 1:
If a person would be deficient in all 3 forms of PFK-1, this person would .
A. Have lower than normal glycogen stores.
B. Have more mitochondrial activity than normal.
C. Be dead.
D. Produce more energy per glucose molecule because glycolysis would be unregulated.

It is now Monday morning and you are ready to start seeing patients with Dr. Saccharo.

peachdonkey87

Phosphofructokinase (PFK1) is a glycolytic enzyme that catalyzes the irreversible transfer of a phosphate from ATP to fructose -6-phosphate to form fructose-1, 6- bisphosphate.

fructose-6-phosphate + ATP --> fructose-1,6-bisphosphate + ADP

PFK1 is the key regulatory enzyme for glycolysis. When ATP levels are high in the cell, the cell no longer needs metabolic energy production to occur. In the case of these high energy levels, PFK1's activity is inhibited by allosteric regulation by ATP, which essentially closes the valve on the flow of carbohydrates through glycolysis.

Recall that allosteric regulators bind to a different site on the enzyme rather than the active (catalytic) site. ATP binds to the regulatory site and decreases PFK1 activity. ATP bound in the regulatory site acts as a modulator by lowering the affinity of PFK1 for its substrate, fructose-6-phosphate. AMP on the other hand, which is generated when the cell is in a low energy state binds to allosteric site and increases enzyme activity.

7. The enzyme PFK1 is an example of a non-regulatory enzyme or regulatory enzyme?

8. How is PFK regulated?

A. It is not regulated because it is a non-regulatory enzyme

B. allosteric enzyme regulation

C. covalent enzyme regulation

D. or proteolytic cleavage enzyme regulation?

9. What is the substrate and to which site on the enzyme does it bind? Which compounds are the positive and negative effectors?

10. In which conformational state would the enzyme be when negative inhibitors bind and in which conformational state would the enzyme be when positive inhibitors bind?

11. PFK1 is a heterotropic or homotropic regulatory enzyme?

12. Draw (or insert the picture from your course packet available on Canvas) the graph that corresponds to this reaction. Your graph should include the activity of PFK without bound effectors, with bound positive effector, and with bound negative effector. Label (or describe) each line to distinguish these along with which molecules are positive and negative effectors.

13. How does Vmax and K0.5 change with the positive and negative effectors?

You are given responsibility for purifying a protein, the isozyme phosphofructokinase-1 C (PFK-1 C, an enzyme of glycolysis). There are three isozymes (multiple forms of an enzyme) of PFK-1 and they are designated A, B, and C. The A isozyme (MW = 84,000 dal) is found in the muscle and the brain; the B isozyme (MW = 80,000 dal) is found in the liver and the brain; and the C isozyme (MW = 86,000 dal) is found in the brain. Following a protocol for the purification, you proceed through the steps below. Your advisor asks you questions about your techniques. Provide the answers below

You proceed with the purification using the soluble protein fraction that resulted from the centrifugation steps above. You run the soluble proteins over an ATP-Sepharose chromatographic column. This is an affinity column in which ATP is covalently linked to a polysaccharide bead (FYI â ATP is a substrate of the PFK enzyme). The sample is loaded on top of the column, washed with a low-salt buffer, followed by a wash with a high salt buffer. The proteins are then eluted from the column.

After the soluble proteins are added to the column, do you expect PFK-1C to flow directly through the column or will its migration be slowed? Explain your reasoning.

What is the purpose of washing with a low salt and then a high salt buffer? Why are both washes needed?