Biology FACTORS AFFECTING ENZYME ACTIVITY

KEY TOPICS

star Nature of Enzyme Action
star Factors Affecting Enzyme Activity

NATURE OF ENZYME ACTION

● Each color{brown}("enzyme (E)") has a color{brown}("substrate (S)") binding site in its molecule so that a highly reactive color{brown}("enzyme-substrate complex (ES)") is produced.

● This complex is short-lived and dissociates into its color{brown}("product(s) P") and the unchanged enzyme with an intermediate formation of the color{brown}("enzyme-product complex (EP).")

● The formation of the color{violet}("ES complex ") is essential for catalysis.

color{red}( E + S ‡ˆ ˆˆ ˆˆ†ˆ ES → EP → E + P)

● The color{brown}("catalytic cycle") of an color{violet}("enzyme action") can be described in the following steps:

1. First, the substrate binds to the color{violet}("active site") of the color{violet}("enzyme, fitting") into the color{violet}("active site.")

2. The binding of the substrate induces the color{violet}("enzyme") to alter its color{violet}("shape, fitting") more tightly around the substrate.

3. The color{violet}("active site") of the enzyme, now in color{violet}("close proximity") of the substrate breaks the chemical bonds of the substrate and the new color{violet}("enzyme- product complex") is formed.

4. The color{violet}("enzyme") releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and run through the color{violet}("catalytic cycle") once again.

FACTORS AFFECTING ENZYME ACTIVITY

● The color{violet}("activity of an enzyme") can be affected by a change in the conditions which can alter the color{violet}("tertiary structure") of the color{violet}("protein.")

● These include color{brown}("temperature, pH, change in substrate concentration") or binding of specific color{brown}("chemicals") that regulate its activity.

color{green}(star "Temperature and pH")

● color{violet}("Enzymes") generally function in a narrow range of color{violet}("temperature and pH.")

● Each enzyme shows its highest activity at a particular color{violet}("temperature and pH") called the color{brown}("optimum temperature") and color{brown}("optimum pH.")

● Activity declines both below and above the color{violet}("optimum value.")

● Low temperature preserves the color{violet}("enzyme ") in a temporarily color{violet}("inactive state") whereas high temperature color{violet}("destroys enzymatic activity") because proteins are color{brown}("denatured") by color{violet}("heat.")

color{green}(star "Concentration of Substrate")

● With the increase in substrate concentration, the color{violet}("velocity of the enzymatic reaction") rises at first.

● The reaction ultimately reaches a color{brown}("maximum velocity" (V_("max"))) which is not exceeded by any further rise in concentration of the substrate.

● This is because the color{violet}("enzyme molecules") are fewer than the color{violet}("substrate molecules") and after saturation of these molecules, there are no free color{violet}("enzyme molecules") to bind with the additional substrate molecules.

color{green}(star "Presence of Inhibitors")

● The color{violet}("activity of an enzyme") is also color{violet}("sensitive") to the presence of specific chemicals that color{violet}("bind to the enzyme").

● When the color{violet}("binding of the chemical shuts off enzyme activity"), the process is called color{brown}("inhibition") and the chemical is called an color{brown}("inhibitor.")

● When the color{violet}("inhibitor") closely resembles the substrate in its color{violet}("molecular structure") and color{violet}("inhibits the activity of the enzyme"), it is known as color{brown}("competitive inhibitor.")

● Due to its close structural similarity with the substrate, the color{violet}("inhibitor competes") with the substrate for the substrate color{violet}("binding site of the enzyme.")

● Consequently, the substrate cannot bind and as a result, the color{violet}("enzyme action") declines, e.g., color{violet}(" inhibition") of color{brown}("succinic dehydrogenase by malonate") which closely resembles the substrate color{brown}("succinate") in structure.

● Such color{violet}("competitive inhibitors") are often used in the control of color{brown}("bacterial pathogens.")