Factors Affecting Enzyme Activity

10 Key excerpts on "Factors Affecting Enzyme Activity"

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  eBook - ePub

  Cambridge O Level Biology 5090

  • Azhar ul Haque Sario, Azhar ul Haque Sario(Authors)
  • 2023(Publication Date)
  • tredition

    (Publisher)

  Monitoring reactant and product concentrations to trace the course of enzyme-catalyzed reactions is a cornerstone technique in biochemistry. It offers invaluable insights into enzyme efficiency and regulation, impacting a wide array of scientific and medical applications. This understanding paves the way for progress in areas like drug development, disease diagnosis, and biotechnological innovation. As scientific research advances, emerging methodologies and technologies continually refine our capability to examine these essential biological catalysts, deepening our grasp of the molecular foundations of life.

  The investigation into how temperature and pH affect enzyme activity is a crucial aspect of biochemistry, with significant implications in various biological processes and practical applications. This comprehensive exploration aims to provide a detailed understanding of these influences.

  Introduction to Enzymes and Their Importance Enzymes are biologically active proteins that play a pivotal role in facilitating and accelerating biochemical reactions within living organisms. These catalysts are essential for numerous physiological processes, including digestion, metabolism, DNA replication, and many others. Their ability to lower the activation energy of reactions is central to their functionality.

  Impact of Temperature on Enzyme Activity Fundamental Concepts: Temperature influences enzyme activity profoundly. Enzymes, being proteins, have a specific three-dimensional structure crucial for their function. The rate of biochemical reactions generally increases with temperature due to enhanced kinetic energy, leading to more frequent collisions between enzyme and substrate.

  Optimal Temperature: Each enzyme has an optimal temperature range where its activity is maximized. This is typically around the normal body temperature for enzymes in humans (approximately 37°C). Within this range, enzymes exhibit maximum efficiency.

  Low Temperatures: At low temperatures, the kinetic energy of molecules decreases, leading to reduced collisions between enzymes and substrates. This results in a diminished rate of reaction.

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  eBook - ePub

  Medicinal Chemistry

  An Introduction

  • Gareth Thomas(Author)
  • 2011(Publication Date)
  • Wiley

    (Publisher)

  The mechanisms of the reactions at the active sites of enzymes have been widely investigated. There is now no doubt that the increased speed of enzyme-catalysed reactions is due in part to the close proximity and the correct alignment of the reactants at the active site. A detailed knowledge, obtained from X-ray crystallography, of the three-dimensional structures of the enzyme and bound substrate plus other experimental evidence means that in many cases the details of enzyme action have been established. This has resulted in the proposal of reaction mechanisms for a number of processes. However, it should be realised that each mechanism is specific for the enzyme-substrate system under consideration.

  9.7 The general physical factors affecting enzyme action

  The main physical factors affecting enzyme action are the relative concentrations of the enzyme and substrate, the pH and the temperature. If the concentration of the substrate is kept constant, the rate of the reaction increases with an increase in enzyme concentration. However, if the concentration of the enzyme is kept constant, as is likely in biological processes, and the concentration of the substrate is increased, the rate of reaction increases to a maximum value known as the saturation value (Fig. 9.11a ). This maximum rate corresponds to the saturation of all the available active sites of the enzyme. In the case of enzymes that are under feedback control (see section 9.4.2) the curve is sigmoidal (Fig. 9.11b ), as against hyperbolic for enzymes not under feedback control but still regulated by a modulator, that is, under allosteric control.

  Figure 9.11

  The effect of concentration on the rate of allosteric (a) modulated and (b) feedback-regulated enzyme-catalysed reactions

  Enzymes are only usually effective over specific ranges of pH characteristic of the enzyme (Fig. 9.12 ). These ranges usually correspond to the pH of the environment in which the enzyme occurs. Outside this range the enzyme may undergo irreversible denaturation

  Figure 9.12

  The effect of pH and temperature on the rates of enzyme-catalysed reactions

  with subsequent loss of activity. Initially an increase in temperature will usually result in an increase in the rate of an enzyme-controlled reaction. However, enzymes are sensitive to temperature and once it increases beyond a certain point the protein irreversibly denatures and the enzyme becomes inactive. An enzyme’s operating temperature range will normally correspond to about that of its normal environment.

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  eBook - ePub

  Biomolecules

  From Genes to Proteins

  • Shikha Kaushik, Anju Singh(Authors)
  • 2023(Publication Date)
  • De Gruyter

    (Publisher)

  Figure 3.5: Peptide hydrolysis by chymotrypsin.

  3.4  Factors Affecting Enzyme Activity

  The activity of an enzyme is affected by its environmental conditions. Any change in the solution conditions alters the rate of reaction and hence the progress of an enzyme-catalyzed reaction. In nature, organisms adjust the conditions of their enzymes to produce an optimum rate of reaction, where necessary, or they may have enzymes that are adapted to function well in extreme conditions where they live. There are several factors which affect the rate at which enzymatic reactions proceed such as pH, temperature, ionic strength, enzyme concentration, substrate concentration, and the presence of any activators or inhibitors.

  3.4.1  pH – Acidity and Basicity

  pH refers to the hydrogen ion (H+ ) concentration in solution, and it measures the acidity and basicity of a solution. The pH scale ranges from 0 to 14; however, negative pH values and values above 14 are also possible. Lower pH values mean higher H+ concentrations and lower OH– (hydroxide ion) concentrations.

  The activity of an enzyme is its ability to function, and it can be defined as the micromoles of product formed per minute under standard conditions:

  1 u n i t

  U

  = 1

  μ m o l / m i n

  The activity of an enzyme varies with the pH of the solution. As the pH of the solution is lowered, an enzyme will gain a proton (H+ ); similarly the enzyme will lose a proton on raising the pH of the solution. Under both conditions, the ionization state of acidic and basic amino acids will be changed, which can interfere with the hydrogen bonding and ionic interactions that help in maintaining the tertiary structure of protein molecules. This interference causes a change in shape of the enzyme, and most importantly disrupts its active site. Any change in the shape or polarity of the active site would minimize the interaction between the substrate and enzyme, and hence affects the rate of biochemical reaction. Each enzyme has an optimum pH – pH at which the activity of an enzyme is maximum, and at this pH, the shape of the active site is best suited to the shape of the substrate. Any change in pH above or below the optimum pH will quickly cause a decrease in the rate of reaction as enzyme molecules will have active sites whose shapes are not, or less, complementary to the shape of their substrate. The effect of pH on the rate of an enzyme-catalyzed reaction is displayed in Figure 3.6

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  eBook - ePub

  Medical Biochemistry

  • Antonio Blanco, Gustavo Blanco(Authors)
  • 2017(Publication Date)
  • Academic Press

    (Publisher)

  m value is usually considered the natural or “physiological” substrate for that enzyme.

  Temperature . The rate of a chemical reaction increases, when temperature rises, as a result of the increase in kinetic energy in the system. Within certain limits, enzyme-catalyzed reactions follow this behavior and the speed of many biological reactions almost doubles for every 10°C increase in temperature. This activity–temperature increase in the reaction rate is called Q 10 or temperature coefficient . If concentrations of enzyme, substrate, and other factors of the reaction medium are maintained constant and the reaction activity is determined at increasing temperatures, the curve shown in Fig. 8.7 is obtained.

  Figure 8.7   Effect of temperature on enzyme activity. Enzyme activity is expressed as percent of the maximal activity achieved. Experimental points are not shown.

  Although enzyme activity increases with temperature, a maximum value is reached, which corresponds to the optimal temperature for the catalytic activity of a given enzyme. Above this temperature, enzyme activity rapidly drops.

  For the great majority of warm-blooded animal enzymes, the optimal temperature is approximately 37°C. Beyond that temperature, activity decreases, and approaching 60°C, most of the enzymes are completely inactivated. This inactivating effect of temperature, which occurs above 40°C, is explained by the denaturing action that heat has on the molecular structure of the enzyme.

  pH . If enzyme activity is measured at different pH values, maintaining other conditions constant, the effect of the hydrogen ion concentration becomes apparent (Fig. 8.8 ).

  Figure 8.8   Effect of pH on enzyme activity. Enzyme activity is expressed as a percent of the maximum activity achieved. Experimental points are not shown.

  For most enzymes, optimum activity is between pH 6 and 8. Below or above these values, the reaction rate drops more or less rapidly. However, exceptions include gastric pepsin which exhibits maximal activity at acidic pH (around 1.5). Acid phosphatase, abundant in the male prostate, exhibits its greatest activity at pH 5 and alkaline phosphatase from bone and other organs has optimal activity at a pH of 9.5.

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  MCAT Biochemistry Review 2024-2025

  Online + Book

  • (Author)
  • 2023(Publication Date)
  • Kaplan Test Prep

    (Publisher)

  y-intercepts in a Lineweaver–Burk plot represent?

  • x-intercept: ________________________________________
  • y-intercept: ________________________________________
• What is enzyme cooperativity? ________________________________________

2.4 Effects of Local Conditions on Enzyme Activity

LEARNING OBJECTIVES

After Chapter 2.4, you will be able to:

• Predict how changes to the environment will alter enzyme behavior
• Estimate the ideal pH and temperature for enzymes found in the human body
The activity of an enzyme is heavily influenced by its environment; in particular, temperature, acidity or alkalinity (pH), and high salinity have significant effects on the ability of an enzyme to carry out its function. Note that the terms enzyme activity, enzyme velocity, and enzyme rate are all used synonymously on the MCAT.

Temperature

Enzyme-catalyzed reactions tend to double in velocity for every 10°C increase in temperature until the optimum temperature is reached; for the human body, this is 37°C (98.6°F or 310 K). After this, activity falls off sharply, as the enzyme will denature at higher temperatures, as shown in Figure 2.7 . Some enzymes that are overheated may regain their function if cooled. A real-life example of temperature dependence occurs in Siamese cats. Siamese cats are dark on their faces, ears, tails, and feet but white elsewhere. Why? The enzyme responsible for pigmentation, tyrosinase, is mutated in Siamese cats. It is ineffective at body temperature but at cooler temperatures becomes active. Thus, only the tail, feet, ears, and face (cooled by air passing through the nose and mouth) have an active form of the enzyme and are dark.
Figure 2.7 Effects of Temperature and pH on the Rate of Enzyme Action

pH

Most enzymes also depend on pH in order to function properly, not only because pH affects the ionization of the active site, but also because changes in pH can lead to denaturation of the enzyme. For enzymes that circulate and function in human blood, this optimal pH is 7.4, as shown in Figure 2.7 . A pH < 7.35 in human blood is termed acidemia. Even though it’s more basic than chemically neutral 7.0, it is more acidic than physiologically