Question

What is the rate-limiting enzyme in glycolysis? What activates or inhibits that enzyme?

a) The rate-limiting enzyme is lactate dehydrogenase, activated by oxygen
b) The rate-limiting enzyme is hexokinase, inhibited by ATP and activated by ADP
c) The rate-limiting enzyme is citrate synthase, activated by glucose
d) There is no rate-limiting enzyme in glycolysis

Answer 1

b) The rate-limiting enzyme is hexokinase, inhibited by ATP and activated by ADP. The rate-limiting enzyme in glycolysis is phosphofructokinase. It is activated by AMP and ADP and inhibited by ATP, citrate, and a lower pH. Another rate-limiting enzyme is pyruvate kinase, which is activated by fructose-1,6-bisphosphate and inhibited by ATP.

Step-by-step explanation:

Phosphofructokinase is the main enzyme controlled in glycolysis. It is a rate-limiting enzyme that catalyzes the phosphorylation of fructose-6-phosphate to produce fructose-1,6-bisphosphate. The activity of phosphofructokinase is regulated by several factors. High levels of ATP or citrate, or a lower pH, decrease the enzyme's activity. An increase in citrate concentration can occur due to a blockage in the citric acid cycle. The enzyme is also activated by AMP and ADP.

Another rate-limiting enzyme in glycolysis is pyruvate kinase, which catalyzes the last step of glycolysis. Its activity is increased when fructose-1,6-bisphosphate levels increase. It is also regulated by ATP, which acts as a negative allosteric effector. Pyruvate kinase is inhibited when no more energy is needed, and alanine supply is adequate.