Enzyme Definition and Theories
The concept of an enzyme is exceptionally important to understand in regards to biology, biochemistry, as well as biotechnology. The term “enzyme” refers to a biological catalyst, which increases the rate of a certain chemical reaction occurring in the cell. Enzymes are mostly proteins since they are made up of amino acids. However, RNA molecules are also categorized as enzymes even though they do not have proteins on them. Enzymes are reusable since they are not harmed throughout the reaction they become a part of. According to the National Human Genome Research Institute (2021), a cell cam contain up to “thousands of different types of enzyme molecules, each specific to a particular chemical reaction” (para. 1). In addition, it is crucial to mention enzymes are highly selective in terms of reactions and substrates they are going to catalyze. Substrates are known as the molecules that enzymes interact with.
As for the theories that explain how enzymes function, there are two primary approaches utilized to examine the interaction between an enzyme and substrates. The first one is the lock-and-key model, which posits that a specific area of an enzyme is shaped perfectly to accommodate a precise substrate type exclusively. The second theory, known as the induced-fit model, explains that enzymes and substrates have to accommodate each other by changing their shapes.
How an Allosteric Enzyme Functions
Allosteric enzymes are a unique phenomenon, which is essential to discuss as well. They have similar characteristics to enzymes, such as the fact that they are also biological catalysts. Yet, their behavior does not follow the Michaelis-Menten model. Such enzymes have a regulatory role since they initiate the development of complex enzyme-substrate links, which either foster or obstruct binding activities that might follow. What makes an allosteric enzyme unique is that it has an allosteric site above an active site. Thus, the process of binding with a substrate occurs with the help of the allosteric site. This allows allosteric enzymes to be more flexible and adapt to different environments rather quickly. Furthermore, this distinct property amplified such enzymes’ catalytic activities. Beeram et al. (2019) note that “allosteric enzymes are regulated by various means like phosphorylation and covalent modification” (p. 180). To sum it all up, allosteric enzymes possess a unique property, enabling them to be more adaptable, which is essential for their roles as regulators.
Factors Affecting the Rate of Enzyme Activity
There are a variety of factors, which have the ability to dictate the rate of enzyme activity. This rate essentially refers to the speed of enzyme catalyzation, which then leads to a reaction resulting in a substrate turning into a product. Some of the factors that influence the rate of enzyme activity include enzyme concentration, substrate concentration, proton concentration (pH), as well as temperature. As for the effect of enzyme concentration, it is important to note that there is a direct proportion between the reaction’s initial rate and enzyme concentration. If all the other factors that affect the rate of enzyme activity remain the same, increasing initial concentration is going to result in a proportional rise of the enzyme-catalyzed reaction’s initial velocity. For instance, increasing concentration of enzymes four times, in comparison to the initial enzyme concentration, will lead to the increase of the rate of enzyme activity four times. Similarly, increasing substrate concentration will also result in increased initial velocity, under the conditions that all the other conditions remain constant. However, the velocity will only rise to a certain level, indicating a maximum velocity value.
In regards to the effect of proton concentration (pH), if all the other modifying conditions remain the same, altering pH will result in the decrease of enzyme activity. There is an optimal pH level that enzymes should be at because changes in this level may lead to protein denaturation or proton et dissociation. Lastly, when it comes to temperature, higher temperatures lead to increased enzyme activity, and vice versa. However, when the temperature reaches a certain point (above 50 degrees Celsius), denaturation of proteins occurs, resulting in absolute inactivity.
Defining Competitive and Non-Competitive Inhibition
In order to clearly define competitive and non-competitive inhibition, it is first important to break down some of the basic terminology behind these concepts. Thus, an inhibitor is a molecule, which is raked with obstructing the normal process of binding between a substrate and an enzyme. It prevents the development of an enzyme-substrate link, which, in turn, disrupts the formation of the end product. Based on how they function, enzymes can be either competitive or non-competitive. To ensure that both concepts are articulated and explained accurately and in detail, it is crucial to examine the normal enzyme reaction first. In such a reaction, an enzyme possesses an active site for a substrate to bind to, which occurs in one of two ways. Substrates and enzymes either complement each other in terms of shape and attributes or have to alter, which is known as an induced fit. All in all, the end result of a normal enzyme reaction is a product, which has once been a substrate.
However, activity of enzymes is sometimes inhibited in numerous ways. Competitive inhibition refers to the process of a molecule similar in properties to the substrate binding to the active site. The molecule can resemble the substrate either chemically or structurally. Surely, this prevents an actual substrate from binding, which creates competition between the inhibitor and the substrate. Pamidipati and Ahmed (2020) argue that “competitive inhibition is usually overcome by increasing the substrate concentration, thereby increasing the probability of enzyme-substrate binding and decreasing the effect of the inhibitor” (p. 434). Thus, ensuring that the concentration of substrates is higher can lower the risk of competitive inhibition and reduce its overall impact.
Non-competitive inhibition, on the other hand, does not imply active competition between a substrate and an inhibitor since the latter binds to other regions of an enzyme, rather than an active site. However, in certain cases, the inhibitor binds in such a way that it blocks the pathway for the substrate to bind to an active site. In other cases, the reaction of the substrate and the enzyme is disrupted due to the inhibitor altering the structure or shape of the enzyme molecule, making the active site useless. This conformational change that occurs as a consequence of non-competitive inhibition eliminates any possibility of shared specificity between an enzyme and a substrate. Scientists refer to such instances as allosteric inhibition. In fact, an enzymatic site, rather than an active one, is defined as an allosteric site. Furthermore, it is crucial to mention that it is impossible to reduce or mitigate the impact of non-competitive inhibition through substrate concentration increase, which is the case for competitive inhibition.
References
Beeram, E., Bysani, D., Pallavi, C., & Thyagaraju, K. (2018). Enzyme kinetics of RNase present in testes. International Journal of Molecular Biology, 3(4), 178-180. Web.
National Human Genome Research Institute. (2021). Enzyme. Genome. Web.
Pamidipati, S., & Ahmed, A. (2020). A first report on competitive inhibition of laccase enzyme by lignin degradation intermediates. Folia Microbiol, 65, 431-437. Web.