`star` Nature of Enzyme Action
`star` Factors Affecting Enzyme Activity


● 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.


● 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.")`