There Are Four Enzymes That Can Catalyze the First Step

question 3

Multiple Choice

There are four enzymes that can catalyze the first step of glycolysis. They are hexokinases I, II and III and glucokinase hexokinase IV) . Hexokinases I, II and III have K_m values near 0.1 mM. Glucokinase has a K_m range of 2-5 mM. If after a heavy meal the blood glucose level rises to 8 mM which statement will be true?

• A) At this high blood glucose level all four hexokinases are saturated with substrate.
• B) Hexokinases I, II and III are catalyzing at their maximum rate, but glucokinase can still respond to increases in blood glucose levels.
• C) None of the enzymes is saturated. All of them help to increase the rate of glycolysis.
• D) The flux through glucokinase will be extremely low. The only significant catalysis is done by hexokinases I, II and III.

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