Biochemistry Lecture 10 PDF

Biochemistry Enzymes LECTURE (10) DR. El-Sawy 1  Biochemistry Enzymes 1. Enzyme concentra...

Biochemistry Enzymes LECTURE (10) DR. El-Sawy 1  Biochemistry Enzymes 1. Enzyme concentration 5. Time 2. Substrate concentration 6. Temperature 3. Concentration of coenzymes 7. pH 4. Concentration of ion activators 8. Inhibitors Coenzymes/ ion activators/ inhibitors S+E P+E PH/ temp/ time  Rate of enzyme action is directly proportional to enzyme concentration provided sufficient supply of substrate & constant conditions.. Enzyme concentration  Rate of reaction increases as the substrate concentration increases up to certain point at which the. Substrate reaction rate is maximal (Vmax.) concentration  At Vmax, enzyme is completely saturated with substrate, Then any increase in substrate concentration don't affect the reaction rate. DR. El-Sawy 2  Biochemistry Enzymes Michaelis constant (Km) : Definition:  Substrate concentration that produces 1/2 maximum velocity of enzyme (1/2 Vmax)  Km = 1/2 Vmax Enzymes with low Km Enzymes with high Km affinity  High affinity to substrate  Low affinity to substrate velocity  Maximal  Maximal substrate  low  high concentration  Hexokinase  Glucokinase Acts on glucose at low Acts on glucose at high Example concentration (fasting concentration (fed state). state) DR. El-Sawy 3  Biochemistry Enzymes  Rate of reaction increases gradually with ↑↑ in temperature until reach a maximum at optimum temperature (37-40°C).  After optimum temperature, the rate of reaction decrease due to denaturation of the enzyme (60-65°C).  The effect of temperature on reaction rate is due to: A. ↑ Initial energy of substrate →↓ activation energy. B. ↑ collision of molecules.. Temperature  In conjugated enzymes:. Coenzymes Concentration ↑↑ coenzyme concentration → ↑↑ reaction rate.  ↑↑ in metal ion activator → ↑↑ reaction rate.  Many enzymes are activated by ions : A. Chloride ion activate salivary amylase. Ion B. Calcium ion activate thrombokinase enzyme activators Concentration DR. El-Sawy 4  Biochemistry Enzymes  Each enzyme has an optimum PH at which its activity is maximal. Optimum PH of pepsin = 1.5-2 (Acidic) Optimum PH of pancreatic lipase = 7.5-8 (Alkaline) Optimum PH of salivary amylase = 6.8 (Slightly acidic). PH  Change of PH above or below optimum PH ↓ rate of enzyme action due to: 1. Change in PH will affect ionization state of both enzyme & substrate. 2. Marked change in PH will cause enzyme denaturation.  Rate of reaction is decreased by time.  Due to:. Time A. ↓↓ substrate concentration. B. Accumulation of products. C. Change in PH.  Presence of enzyme inhibitor → decreases or stops the enzyme activity.. Enzymes  Enzyme inhibitors may be: inhibitor 1- Competitive inhibitors. 2- Non competitive inhibitors. DR. El-Sawy 5  Biochemistry Enzymes DR. El-Sawy 6