What are the factors affecting Enzyme Activity?

Recap

What are enzymes? Biological catalysts made up of proteins

Function of Enzymes Enzymes speed up the rate of chemical reactions in the body; both breaking down (e.g.: starch into maltose) and building up reactions. (e.g: amino acids into proteins). Enzymes lower the activation energy required to start a chemical reaction

Characteristics of Enzymes Enzymes are highly specific in action. Enzymes remain chemically unchanged at the end of the reaction. Enzymes are required in minute amounts.

I. Name that Enzyme !!! Protein ase Substrate Name + -ase

I. Name that Enzyme !!! Lipid ase

Mode of Action Substrate fits in the enzyme active site, just like a key fits into a lock. An enzyme-substrate complex is formed. Chemical reactions occur at the active site and products are formed.

What are the factors affecting Enzyme Activity?

Hydrogen peroxide  water and oxygen catalase Hydrogen peroxide  water and oxygen

Temperature and Enzyme Activity

0°C Low temperatures  low Kinetic Energy of enzymes and substrates. No/Very few enzyme-substrate complexes are formed. Enzymes are inactivated.

20°C (increasing temperature) Increasing the temperature will lead to the increase in kinetic energy of enzyme and substrate molecules. Enzyme and substrate molecules move with increasing speed and collide more frequently with each other. This increases the rate of enzyme-substrate complex formation This increases the rate of enzyme-substrate complex formation and product formation. Rate of reaction increases

37°C As the temperature continues to increase, the rate of enzyme activity also increases until the optimal temperature is reached. Optimal temperature is the temperature at which the enzyme works best. Rate of product formation is highest!

Beyond Optimal Temperatures At high temperatures (>60°C), weak bonds within the enzyme molecule are broken Enzyme loses its shape and its active site. Loss of shape leads to a loss of function. Enzyme is said to have denatured Denaturation is the change in 3D structure of an enzyme or any other protein caused by heat or chemicals such as acids or alkali, causing it to lose its function.

Denaturation Different enzymes denature at different temperatures. Most enzymes denature at temperatures higher than 60°C. However, there are some enzymes that stay active even at high temperatures like 80°C (Enzymes in the bacteria Thermus aquaticus)

Effect of pH on enzyme activity Enzyme works best within a narrow pH range Each enzyme works best at particular pH, known as its optimum pH level. At extreme pH levels, enzymes lose their shape and function and become denatured.

Effect of pH on enzyme activity

pKa and Amino Acids pKa determines at what pH acidic hydrogen atoms will dissociate (break apart from) from the amino acid.

Example Glutamic Acid pKa carboxylic acid= 2.10 pKa amino= 9.47 pKa R-group= 4.07

Amino Acid Charges and Protein Folding

Effect of Concentration on Enzyme Activity

Inhibition and Activation Enzyme inhibitors slow down the rate of a reaction. Sometimes this is a necessary way of making sure that the reaction does not proceed too fast, at other times, it is undesirable Enzyme activators are molecules that bind to enzymes and increase their activity. They are the opposite of enzyme inhibitors. These molecules are often involved in the allosteric regulation of enzymes in the control of metabolism.

Competitive inhibition Reversible inhibitors: Competitive reversible inhibitors: these molecules have a similar structure to the actual substrate and so will bind temporarily with the active site. The rate of reaction will be closer to the maximum when there is more “real” substrate, (e.g. arabinose competes with glucose for the active sites on glucose oxidase enzyme).

Noncompetitive Inhibition Reversible inhibitors: Non-competitive reversible inhibitors: these molecules are not necessarily anything like the substrate in shape. They bind with the enzyme, but not at the active site. This binding does change the shape of the enzyme though, so the reaction rate decreases.

Irreversible inhibitors: These molecules bind permanently with the enzyme molecule and so effectively reduce the enzyme concentration, thus limiting the rate of reaction. Cyanide irreversibly inhibits the enzyme cytochrome oxidase found in the electron transport chain. If this cannot be used, death will occur