Important Factors That Influence Enzyme Activity Creator : Lyubomir Penelov

Enzymes are essential for almost all the chemical reactions that take place inside living cells. However, the activities of the enzymes can be enhanced or inhibited by a number of factors. In this article, we are talking about all those factors that affect enzyme activity.

Enzyme Activity Explained An enzyme can increase the speed of a chemical reaction manifold. You will be surprised to know that studies have found that it can make a chemical reaction 10 billion times faster. The chemical substances that are present at the start of a biochemical process is termed as substrates which undergo chemical change(s) to form one or more end products. Basically, the active site of the enzymes forms a temporary bond with the substrate. During this time, an enzyme lowers the activation energy of the participant molecules which in turn speeds up the reaction. After the reaction is over, the newly formed product leaves the surface of the enzyme and the enzyme gets back its original shape. Thus, you can say it participates in the reaction without undergoing any physical or chemical change. Therefore, the same enzyme is used again and again for the specific process.

Human glyoxalase I. Two zinc ions that are needed for the enzyme to catalyze its reaction are shown as purple spheres, and an enzyme inhibitor called S-hexylglutathione is shown as a space-filling model, filling the two active sites

Factors Influencing Enzyme Activity

Change in Temperature All enzymes need a favorable temperature to work properly. The rate of a biochemical reaction increases with rise in temperature. This is because the heat enhances the kinetic energy of the participant molecules which results in more number of collisions between them. On the other hand, it is mostly found that in low temperature conditions, the reaction becomes slow as there is less contact between the substrate and the enzyme. However, extreme temperatures are not good for the enzymes. Under the influence of very high temperature, the enzyme molecule tends to get distorted, due to which the rate of reaction decreases. In other words, a denatured enzyme fails to carry out its normal functions. In the human body, the optimum temperature at which most enzymes become highly active lies in the range of 95 °F to 104 °F (35 °C to 40 °C). There are some enzymes that prefer a lower temperature than this.

Change in pH Value The efficiency of an enzyme is largely influenced by the pH value of its surroundings. This is because the charge of its component amino acids changes with the change in the pH value. Each enzyme becomes active at a certain pH level. In general, most enzymes remain stable and work well in the pH range of 6 and 8. However, there are some specific enzymes which work well only in acidic or basic surroundings. The favorable pH value for a specific enzyme actually depends on the biological system in which it is working. When the pH value becomes very high or too low, then the basic structure of the enzyme undergoes change(s). As a result, the active site of the enzyme fails to bind well with the substrate properly and the activity of the enzyme gets badly affected. The enzyme may even stop functioning completely.

Substrate Concentration Substrate concentration plays a major role in various enzyme activities. This is obviously because higher concentration of substrate means more number of substrate molecules are involved with the enzyme activity. Whereas, a low concentration of substrate means less number of molecules will get attached to the enzymes. This in turn reduces the enzyme activity. When the rate of an enzymatic reaction is maximum and the enzyme is at its most active state, an increase in the concentration of substrate will not make any difference in the enzyme activity. In this condition, the substrate is continuously replaced by new ones at the active site of the enzyme and there is no scope to add those extra molecules there.

Enzyme Concentration In any enzymatic reaction, the quantity of substrate molecules involved is more as compared to the number of enzymes. A rise in enzyme concentration will enhance the enzymatic activity for the simple reason that more enzymes are participating in the reaction. The rate of the reaction is directly proportional to the quantity of enzymes available for it. However, that does not mean that a constant rise in concentration of enzymes will lead to a steady rise in the rate of reaction. Rather, a very high concentration of enzymes where all the substrate molecules are already used up does not have any impact on the reaction rate. To be precise, once the rate of reaction has attained stability, an increase in the quantity of enzymes does not affect the rate of reaction anymore.

Inhibitors As the name suggests, inhibitors are those substances that have a tendency to prevent activities of the enzymes. Enzyme inhibitors interfere with the enzyme functions in two different ways. Based on this, they are divided into two categories: competitive inhibitors and noncompetitive inhibitors. A competitive inhibitor has a structure which is the same as that of a substrate molecule, and so it gets attached to the activated center of the enzyme easily and restricts the bond formation of enzyme-substrate complex. A noncompetitive inhibitor is the one which brings about change(s) in the shape of the enzymes by reacting with its active site. In this condition, the substrate molecule cannot bind itself to the enzyme and thus, the subsequent activities are blocked.

Allosteric Factors There are some enzymes which have one active site and one or more regulatory sites and are known as allosteric enzymes. A molecule that binds with the regulatory sites are referred to as allosteric factor. When this molecule in the cellular environment forms a weak noncovalent bond at the regulatory site, the shape of the enzyme and its activation center get modified. This change usually decreases the enzyme activity as it inhibits the formation of a new enzyme-substrate complex. However, there are some allosteric activators that promote the affinity between the enzyme and the substrate and influence enzymatic behavior positively.

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