Enzyme Activity in Glycolysis

Matt Turley

Biology 1610-008  Dr. Gazdik Stofer

In our biology course we have learned about enzymes-how they function, why they are so crucial in biological chemical reactions, what excites or inhibits them, and how they relate to energy.  When studying cellular respiration it is easy to think of the process going in one direction.  Seems simple enough, the glucose consumed turns into pyruvate and then enters the citric acid cycle as Acetyl CoA and continues to break down and is converted into usable energy.  It is apparent that after the electron carriers donate their energy to the electron transport chain they are recycled back into the earlier stages of cellular respiration where a hydrogen ion is reattached and the process continues.  I chose this article because it expands on that knowledge I have of cellular respiration, glycolysis specifically, and changed the way I look at enzymes and the process as a whole. 

A group of scientists from the University of Delaware studied an enzyme named “enzyme I” responsible for the conversion of phosphoenolypyruvate (PEP) to pyruvate, the last step in glycolysis.  This study was done with E. Coli, a highly studied bacteria, and the scientists were surprised to learn something about this major metabolic pathway in E. Coli that had been previously misunderstood.  They were able to show that enzyme I not only catalyzed the breakdown of PEP to pyruvate, but could also work in the reverse process.  This step was earlier thought to be irreversible because of a large drop in energy, but this experiment showed otherwise.  From my understanding of enzymes, I would hypothesize that the enzyme has multiple active sites run by competitive inhibition.  If there is excess pyruvate the enzyme will work in reverse.  The scientists noted as well that even when the enzyme was working in the forward direction to create pyruvate there was still some enzyme working in the other direction.  This reminds me of diffusion, where the general flow is from high concentration to low concentration, but there will still be some solute moving in both directions.  We see similar scenarios in chemistry as well, so it would make sense for the same thing to be occurring here. 

After reading this article I no longer look at cellular respiration as a one direction series of reactions, but rather, a flow of energy forwards or backwards wherever makes more use of the energy in the organism.  The article shows as well that gluconeogenesis occurs in glycolysis by creating glucose from acetate and pyruvate.  Eukaryotes are not able to convert light and water to energy as plants do, but they can recreate glucose from its existing building blocks.  One other thing mentioned in the study that I will also point out is that E. Coli is one of the most studied bacterium on the planet and if we are still learning about its most fundamental metabolic processes there must be a lot to still learn by way of enzymes and metabolism.    

Kukich, D. (2017, January 27). OLD ENZYME, NEW ROLE. Retrieved March 04, 2017, from http://www.udel.edu/udaily/2017/january/new-function-enzyme-bacterial-metabolism/