ENZYMES

1. ENZYMES

2. Definition • These are organic substance that accelerates the rate of chemical reactions. • Organic catalyst are enzyme: • 1.Highly specific: catalyze one or two reactions only. • 2.Protein in nature: denatured by heat. • Inorganic catalyst are metals: • 1.Non-specifin:catalize many reactions • 2. Not affected by heat.

3. the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products.

4. Enzymes • Have a recommended name • Suffix –”ase” attached to the substrate of the reaction e.g. glucosidase, ”ambreenase”, “vishaalase” • OR to describe the action performed. e.g. lactate dehydrogenase

5. 4-types of specificity • Optical specificity: acts on one of 2 isomers. e.g maltase acts on α-glycosidase and not β-glycosidase. • Group specificity: the presence of certain group.e.g pepsin acts on peptide bonds. • Absolute specificity: only on one substrate e.g urease acts only on urea. • Relative specificity: acts on group of compound having same type of bonds.lipase acts on different triglycerides.

6. Enzyme activity • Enzymes : simple or conjugated. • Simple: native conformation of protein. • Conjugated protein: holoenzyme. • Apoenzyme + cofactor-> holoenzyme.

8. ..truly amazing substances • Active sites: special pocket where substrate binds (reaction occurs) • Catalyze reaction 10 3 TO 10 17 TIMES FASTER than uncatalyzed reactions • Are highly specific i.e. can catalyze only one type of reaction • Some enzymes require an additional chemical component-COFACTOR e.g. metal ions such as Zn 2+, Fe 2+, Mg 2+

9. ..still on properties • or……….an organic molecule called a coenzyme e.g. NAD+ contains Niacin, FAD contains riboflavin • Holoenzyme - enzyme with its cofactor • Apoenzyme -protein portion of the holoenzyme. • Apoenzyme shows no biologic activity without appropriate cofactor

11. Zymogens • Some enzyme are synthesized as inactive forms called zymogen or proenzyme e.g trypsinogen and pepsinogen. • 1. Zymogen are inactive because their catalytic sites are masked by a polypetide chain. • 2. To activate, cleavage of polypeptide chain.

12. IUBMB Systematic name Enzymes are divided into 6 major classes Suffix “–ase” is attached to describe the chemical reaction catalyzed

13. Oxidoreductases • Transferases • Hydrolases • Lyases • Isomerases • Ligases

14. Oxidoreductases • Enzymes catalyzes an oxidation-reduction reaction between two substrate. • S(oxidised)+Y(reduced) s(reduced) + Y (oxidised).

15. Transferases • Enzyme catalyzes the transfer of a group other than hydrogen from one substrate to another . • SX + Y  S + YX • Glucose +ATP------glucokinase---------------------- gucose-6-phosphate +ADP.

16. Hydrolases • Catalyzes hydrolysis. • A –B --HOH---- AH +BOH • peptidase

17. Lysases • Catalyzes removal of group from substrate by mechanism other than hydrolysis. • Decarboxylase. • Pyruvate acetladehyde + CO2

18. Isomerases Transfer of groups within molecules to yield isomeric forms one substrate and one product are involved,

19. Ligases Formation of C-C, C-S,C-O and C-N bonds coupled to hydrolysis of high energy phosphates e.g. ATP Often referred to as SYNTHETASE

21. LOCK AND KEY HYPOTHESIS

22. Induced fit theory

23. Mechanism of enzyme action • Free energy of the reaction: initial state to final state , consume energy. • Activation energy: absorb energy (activated state or transition state). • The effect of enzyme is to decrease the energy of activation.

25. More properties • Enzyme activity can be regulated i.e. activated or inhibited so rate of product formation suits demands of the cell • Are reusable because they aren't altered in a reaction

26. Factors affecting reaction velocity • Substrate concentration,enzymeconcentration. • Temperature • pH

27. Concentration of enzyme • The amount of enzyme is in a reaction is doubled ,the amount of substrate is converted to product is doubled.

28. Concentration of substrate • At low substrate concentration ,not all enzyme are saturated .So the rate of reaction will increase.(V max) • At higher substrate concentration ,all enzyme molecules get saturated with substrate and any more increase of substrate concentration will result in no increase.

29. Michaelis –menten equation • It describes the dependence of reaction velocity on substrate concentration. • E + S –k1ES • ES breaks down to give enzyme and product. • E + S K-1 E+ S • K2 E + P • So, K1 , K-1,and k2(rate constants)

30. Cont. • Vi=Initial velocity • Vmax =all enzyme are involved in an ES complex. • [s]= increased Substrate • Vi=Vmax [s] [s] + (k1+k2) K-1

31. Cont. • The ratio constants k1 + k2/k-1 as michaelis constant(km) . • So km=k1+ k2 k-1 then vi = Vmax [s] [s] + km Michael equation=km When substrate conc.[s] is equal to km Vi =vmax[s] = vmax [s] =Vmax [s] + km 2S 2

32. Cont. • Thus km can be defined as substrate that produce half maximum velocity.

34. Effect of temperature • The optimal temp. for enzyme activity in human body is that temp similar of that the cells(37˚) • At zero,enzyme inactive • The velocity is almost doubled every 10˚C • At 55˚-60˚C ,most enzyme are denatured and become permanenlty inactive.

36. Effect of pH • The optimal pH activity is that pH at which the enzyme acts maximaly. • Above and below, the reaction decline. • Each enzyme has has its own optimal pH.e.g pancreatic lipase 7.5 • Extream of pH leads to denaturation.

37. Enzyme activators • To activate the enzyme • Metal ions; • Chloride ions which activates salivary amylase and calcium ions which activate blood clotting enzymes. • Zymogen needs other enzyme for activation

38. Inhibition of enzyme activity • Any substance that can diminish the velocity of an enzyme-catalyzed reaction-INHIBITOR • Is Reversible (through non-covalent bonds) or Non-reversible (through covalent bonds) TYPES • Competitive: reversible binding to the same site for the substrate and competes actively for the site.

40. Methotrexate A competitive inhibitor of dihydrofolate reductase - role in purine & pyrimidine biosynthesis Used to treat cancer

41. statin drugs competitively inhibit 1st committed step in cholesterol synthesis catalyzed by HMG CoA Reductase e.g. latorvastatin (Lipitor)-↓ plasma cholesterol levels. • Non-competitive: inhibitor and substrate bind @ diff sites. either free enzyme or ES complex and prevents reaction from running e.g. lead inhibiting ferrochelatase • Enzyme inhibitors can be used as drugs e.g. Penicillin, amoxicillin, ACE inhibitors

42. Allosteric regulation of enzyme activity • allosteric enzyme generally catalyze the irreversible steps in metabolic pathways. • Allosteric mean “other site”,they bind non-covalently at a sit other than active site.