Enzyme not involved in the control of glycolysis

Question

An enzyme not involved in the control of glycolysis is

a) hexokinase

b) triose phosphate isomerase

c) pyruvate kinase

d) phosphofructokinase

c?

Answer 1

This is a difficult question, as all four enzymes are on the glycotic pathway (at steps 1, 5, 10, and 3, respectively).  So the question seems to be which of these steps is regulated and which is not.  By process of elimination:

a) hexokinase catalyzes an irreversible reaction (from glucose to glucose 6-phosphate); its rate is limited by the concentration of glucose 6-phosphate, so if the next regulatory step is inhibited then hexokinase activity will be halted [Lehninger].

d) phosphofructosekinase also catalyzes an irreversible reaction, one which commits the substrate to the rest of the glycolosis pathway, rather than being converted to glycogen [Wikipedia].  The reaction is directly inhibited by ATP by binding to the enzyme, so it provides a feedback mechanism when the cell has enough already [Lehninger].

c) pyruvate kinase catalyzes the final, irreversible energy-intensive step in which ATP is irreversibly synthesized from ADP.  The reaction depends on ionic catalysts (Mg2+/Mn2+ and K+ [Lehninger].  Like phosphofructokinase, pyruvate kinase is inhibited by ATP, and also by acetyl-CoA (which provides an alternate souce for ATP) [Lehninger].

Of these, only (b) does not perform a regulatory function.

Answer 2

c) pyruvate kinase

Answer 3

Yea c. Pyruvate Kinase happens after glycolysis