Factors Affecting Enzyme Activity

Learning Outcomes apply knowledge of proteins to explain the effects on enzyme activity of: pH temperature substrate concentration enzyme concentration competitive inhibitors, and non-competitive inhibitors including heavy metals differentiate between the roles of enzymes and coenzymes in biochemical reactions identify the role of vitamins as coenzymes

Factors affecting enzyme activity Temperature pH Concentration Activation Inhibitors Co-enzymes

What happens to the rate of most chemical reactions as the temperature is increased? Why?

Temperature All enzymes have an optimal temperature Up to this temperature, the reaction rate increases as temperature increases Above this temperature, denaturation of the enzyme occurs (irreversible)

What would you expect to be the optimal temperature of enzymes that function in the human body?

Effect of temperature on enzyme activity Optimal temperature Enzyme activity Temperature

How might a strong acid or base affect a protein?

pH All enzymes have an optimal pH High or low pH causes reduced enzyme activity and denaturation of the enzyme

Effect of pH on enzyme activity Optimal pH Enzyme activity pH

Fig. 6.8

What happens if we increase or decrease the concentration of substrate?

Substrate concentration Increasing the substrate concentration increases the reaction rate only to the point where all enzymes are being used

Effect of substrate concentration Enzyme activity Substrate concentration

What if we add more enzyme? How would this happen in the body?

Enzyme concentration In cells, enzyme concentration is genetically controlled (control of protein synthesis) Increasing the amount of enzyme will increase the reaction rate (as long as substrate is present)

Effect of enzyme concentration Enzyme activity Enzyme concentration

Activation Enzymes may be “turned on” by the presence of another molecule (ex. The addition of a phosphate group, known as phosphorylation)

Enzyme activation

How could you prevent a substrate from binding to an enzyme active site? Would this ever be a desirable outcome?

Inhibition Inhibitors are molecules other than the substrate that bind to the enzyme and inhibit its activity

Competitive inhibition Competitive inhibitors compete with the substrate by binding to the active site

Non-competitive inhibition Non-competitive inhibitors bind to a different site on the enzyme (allosteric site) Change the shape of the enzyme’s active site

Toxic heavy metals such as lead, cadmium and mercury can bind to enzymes causing denaturation Act as non-competitive inhibitors

Feedback inhibition Sometimes the product of the pathway acts as an inhibitor This stops the pathway when there is enough of the product

Fig. 6.9a

Fig. 6.9b

Enzyme cofactors Cofactors or coenzymes are non-protein molecules that assist the enzyme May be inorganic ions ex. Copper, zinc, or iron Often are organic molecules derived from vitamins Function is often to transfer electrons or functional groups (ex. Phosphate) to the substrate

Vitamin deficiency results in interference with enzyme activity in various metabolic pathways (so eat your veggies!)