Need to lower the electric bill? You could learn a thing or two about conservation from your body’s own cells.
Each one possesses a highly evolved system of energy efficiency that consists of regulatory enzymes (1). These catalysts can be activated and deactivated depending on conditions in the cell (1p649-651).
When strategically located as a first step or near-first step of a metabolic pathway, a regulatory enzyme acts as biochemical light switch.(2) The enzyme switches “on” and “off” effectively speeding up or slowing down pathway production and preventing any drain of effort.(2)
An example of three regulatory enzymes in action can be found in glycolysis, the 10-reaction pathway used to produce energy from carbohydrates(1p726):
1. Hexokinase catalyzes the first reaction of the pathway and is inhibited by high concentration of its own product.
2. Phosphofructokinase, the key regulatory enzyme, catalyzes the third reaction and is allosterically inhibited by glycolysis product, ATP, and intermediate, citric acid. This is an example of feedback inhibition.
3. Pyruvate kinase catalyzes the last reaction. Because it is activated by activation of phosphofructokinase through feedforward activation, it is allosterically inhibited by inhibition of phosphofructokinase.
In other words, the last enzyme in the pathway is saying, “First and third one out, don’t forget to turn off the lights.”
1. Denniston, KJ, Topping, JJ & Caret, RL. General, Organic, And Biochemistry, 5th ed. New York: McGraw Hill; 2007
2. Stavrianeas, S. Teaching glycolysis regulation to undergraduates using an electrical power generation analogy. Adv Physiol Educ. 2005;29:128-130. Available at: http://advan.physiology.org/cgi/content/full/29/2/128-a. Accessed on Nov. 15, 2008.