Question

Please explain if you can:

In which of the following is the enzyme properly paired with its allosteric inhibitor?

Multiple answers: You can select more than one option

A- hexokinase: glucose-6-phosphate

B- phosphofructokinase: fructose 2 6-bisphosphate

C- pyruvate kinase: alanine

D- glucokinase: glucose-6-phosphate

(I know it is not B, and I know it is definetly A so far. However, I am unsure about the other two. Please provide an explanation if possible.)

Answer 1

Answers: A,C

Reasons:

A- hexokinase: glucose-6-phosphate-Yes

Hexokinase, the enzyme catalyzing the first step of glycolysis, is inhibited by its product, glucose 6-phosphate.

B. phosphofructokinase: fructose 2 6-bisphosphate- No

Reason: At physiological concentration,PhosphoFructoKinase-1 is almost completely inactive, but interaction with Fru-2,6-P₂ activates the enzyme to stimulate glycolysis and enhance breakdown of glucose.

C. pyruvate kinase: alanine -Yes

Main function of pyruvate kinase is to catalyze the last step of glycolysis; thereby, generating the second ATP of glycolysis and pyruvate. Significant pyruvate kinase regulator is fructose-1,6-bisphosphate (FBP), which serves as an allosteric effector for the enzyme. Addition of ATP causes a marked decrease in the enzyme activity. However, if the FBP is added again to the ATP containing reaction mixture, the inhibition is reversed.L-alanine inhibits the pyruvate kinase, but it appears to be a weaker inhibitor than ATP.

D. glucokinase: glucose-6-phosphate-No

The liver possesses a specialized isozyme of hexokinase called glucokinase that is not inhibited by glucose 6-phosphate.