Enzyme -3. Factors affecting enzyme activity Lecture NO: 1st MBBS Dr Muhammad Ramzan

Enzyme activity - the definition Enzyme activity refers to the catalytic ability of an enzyme to increase the rate of a chemical reaction. Turnover No: is the maximum number of molecules of substrate that an enzyme : Can convert to products per catalytic site per unit time- mint.

Michaelis-Menten equation  It is a set of mathematical expressions to calculate enzyme activity in terms of speed of reaction from measurable laboratory data.

Michaelis Menten equation

Conclusion of the equation Characteristic of Km: It reflects the affinity of the E with S Is equal to the Conc. of S at which reaction velocity is equal to ½ Vmax.Km does not vary with the conc. Of E It is important in competitive inhibition when ↑ in S reverses the Vmax as inhibitor is diluted Vmax: is achieved when all the active sites of E are occupied by the S Vmax: Cannot be achieved in Non completive inhibition as inhibitor binds either to E or ES Complex. ↑in S has no effect as it cannot bind to active site

Measurement of Enzyme activity – Enzyme assay Carbonic Anhydrase – 36million.S/mint Enzymes assays, measure the enzyme activity Carbonic Anhydrase is one of the enzymes having highest Turn Over NO: at 36 million moles per minute. (bicarbonate) More common NOs: are closer to 1000 moles/minute

Activity of Carbonic Anhydrase

Factors affecting the enzyme activity- the significance temperature and pH Although Es speed up chemical reactions, each E works most efficiently under a specific set of conditions. Because almost all Es are proteins, any factor that affects the shape of a protein, may affect E activity High temperature and hostile pH are the major factors affecting the activity of the enzymes

Factors affecting enzyme activity the list of 5 These factors are : Temperature pH of the solution Concentration of substrates and that of enzymes Activators or inhibitor molecules

Enzyme activity and temperature ↑es interaction B/w E and S Temperature/heat is a sort of energy present in the particles that increases their activity or motion Temperature ↑ the rate of reaction and activity of E and S so that both Can Interact with each other more frequently It is more likely that the molecules of S will slot into active site of E leading to the formation of products

Effect of temperature on enzyme activity

High temperature leads to Denaturation temperature > 40C Enzymes are proteins, ↑ of temperature above the optimum level (40 C) causes the protein to lose their : 3 D structure and folding and: 1 Breakage of bonds B/w the functional groups of AAs 2 Change of shape and loss of enzyme function 3 The optimum temperature for majority body enzymes is 37C°

Hostile temperature – Denaturation of E

↑ in Substrate conc. ↑es Enzyme activity up to an optimum level ↑ of substrate ↑the enzyme activity up to an optimum level as more molecules of S have the chance to: Bind with the active site of enzyme Excess of S molecules, reduces the chances of finding an active site and no further ↑ in enzyme activity

↑ substrate conc. ↑ enzyme activity up to optimum limit

↑ in E conc.↑ E activity up to an optimum level This effect is much like that of substrate ↑ in the enzyme conc. increases the rate of enzyme reaction up to an optimum level Further ↑ in enzyme conc. has no effect on the reaction activity as no more S molecules are available However, further ↑ in the substrate molecules, will certainly increase the rate of reaction

↑ in E conc. increases E activity up to an optimum level

pH and activity of enzyme up to an optimum level The pH level of a solution can also affects enzyme activity. Many enzymes can only work within a narrow range ofpH If an enzyme finds itself in a hostile pH range, it could becomes denatured. The optimal pH for many enzymes is 7.0-7.5, but this is not always the case and may be variable

↓ or↑ in pH – affects E activity Salivary and Gastric enzymes Some enzymes, such as in the Gastric secretion work best at an acidic pH of 1.5, (Pepsin and Trypsin) while others such as found in the Salivary and Intestinal secretions work best at a more alkaline pH of 8.0. These include Lingual Lipase and Salivary Amylase in saliva Amylase; Lipase, Protease and carboxy peptidase of pancreatic and Intestinal secretions

Enzyme activity - pH

Hostile pH and E activity – the mechanism S non covalent bonds with E When a substrate slots into the active site of an enzyme It forms temporary bonds (non covalent) with the groups at the active site (Amino acyl groups) These groups are the functional groups of AA in the protein side chains and have important effects on : the shape of enzyme

Hostile pH changes the shape of enzyme If functional groups of AAs of the protein chain are in different order, the S would not bind temporary to the E Because the shape of enzyme will be different This is what happens when the pH changes when increased or decreased

Enzyme activity – the inhibition Enzyme inhibition is the process when a chemical substance binds with the active site of an enzyme and: Inhibits its activity so that active site is no more available to the substrates Such substances are called enzyme inhibitors These inhibitors can cause irreversible or reversible inhibition Reversible inhibition can be competitive and non competitive