Transcript Camp 1
Active Sites – What’s Happening? • 1. Substrate is bound • 2. A reaction is being catalyzed . . . . • e. g. Mechanism of Action: 2 major types For HW- Skip #22.21 – too weird . . . 1. Lock-and-key model of enzyme mechanism. • 2. Induced-fit model Mechanism of Action: 2 major types • 1. Lock-and-key model of enzyme mechanism. • The enzyme is a rigid three-dimensional body. • The enzyme surface contains the active site. CH2 OPO 3 2 CH 2 OPO 3 2 Ph osph oh e xos e CH2 OH O O i some rase H HO OH OH H HO OH H OH HO - D- Gl u cos e -6-ph os ph ate - D-Fru ctos e-6-ph osph ate 1. (key) NOTE: THE REACTION being Catalyzed CH2 OPO 3 2 CH 2 OPO 3 2 Ph osph oh e xos e CH2 OH O O i some rase H HO OH OH H HO OH H OH HO - D- Gl u cos e -6-ph os ph ate - D-Fru ctos e-6-ph osph ate 1. 2. (lock) CH 2 OPO 3 2 CH2 OPO 3 2 Ph osph oh e xos e CH2 OH O O i some rase H HO OH OH H HO OH H OH HO - D- Gl u cos e -6-ph os ph ate - D-Fru ctos e-6-ph osph ate 2. Mechanism of Action 2. Induced-fit model The active site becomes modified to accommodate the substrate CH2 OPO 3 2 CH 2 OPO 3 2 Ph osph oh e xos e CH2 OH O O i some rase H HO OH OH H HO OH H OH HO - D- Gl u cos e -6-ph os ph ate - D-Fru ctos e-6-ph osph ate 1. Induced fit – substrate changes enzyme form/shape once in active site CH2 OPO 3 2 CH2 OPO 3 2 Phosphohe xose CH2 OH O O i some rase H HO OH OH H HO OH H OH HO - D- Gl ucose -6-phosphate - D-Fructose-6-phosphate 2. Mechanism of Action • Figure 22.9 - Competitive inhibition. • the inhibitor fits into the active site, thereby preventing the substrate from entering. Inhibitor got there 1st, Ha ha Mechanism of Action • Figure 22.10 • • Noncompetitive inhibition. the inhibitor binds to allosteric site, ( not active site) This changes conformation of the active site. Alosteric site • The substrate no longer fits (properly). See p. 562-3 Chem. Connections Mechanism of Action • Lock-and-key model & Induced-fit model emphasize the shape of the active site. • However, Chemistry of active site is most important. • Just 5 amino acids participate in active sites of: ≤65% of the enzymes studies to date. • Examples: His > Cys > Asp > Arg > Glu. • Four have either acidic or basic side chains; the fifth has a sulfhydryl group (-SH). Confirming your knowledge • Which of the following is correct describing the Induced-Fit Model of Enzyme action? Substrates fit into the active site: 1. b/c they are exactly the same size and shape 2. By changing their size and shape to match those of the active site 3. By changing the size and shape of the active site Upon binding Challenge Question • Enzymes are long protein chains, > 100 Amino acids • The Active SITE contains only a few amino acids • Explain why other amino acids are present and what would happen to the enzyme activity if significant changes were made to the enzymes Structure. Enzyme Regulation 1. Feedback control 2. Proenzymes 3. Isoenzymes Enzyme Regulation 1. Feedback control: regulation process where the product (of a series of enzyme-catalyzed reactions) • inhibits an earlier reaction in the sequence. fee dback inhi bi ti on (path 2) A E1 B E2 C (path 1) E3 D • The inhibition may be competitive or noncompetitive. (path 1) e.g. cholersterol normally produced in liver, [<100mg/100mL ] (path 2) if > [200mg/100mL] in plasma, liver stops producing . . . Enzyme Regulation (cont.) • 2. Proenzymes (zymogens): inactive form of enzyme must have portion of polypeptide chain removed otherwise not active. • e.g. trypsin, (a digestive enzyme) • synthesized/stored as trypsinogen, no enzyme activity. • Active only after a six-amino acid fragment is removed • Removal of amino acid fragment changes primary + tertiary structure, active form. • 3. Isoenzyme: different form of the same enzyme ( two different forms catalyze the same reaction(s)) Challenge Question • Why not make fully active form of Enzyme(s) all the time? (e.g. trypsinogen trypsin) The Allosteric Effect • Figure 22.12 Binding of regulator to a site other than the active site changes the shape of the active site. Enzymes in Medicine • Enzyme assays useful in medical diagnosis. En zyme Body Flu id D iseas e Diagnosed Alan ine amin otrans ferase (ALT) Acid phosp hatase Alk alin e phosp hatase (ALP) Amylase Serum Hepatitis Prostate cancer Liver or bone dis ease Pan creatic diseas e Serum Serum Serum As partate aminotransferase (AST) Serum, Cereb rosp in al fluid Lactate dehydrogenas e (LD H) Serum Creatin e phosph ok inase (CK) Serum Ph os phohexose isomeras e (PHI) Serum Heart attack or hep atitis Heart attack Heart attack Heart attack Monitor levels 24hr after M.I. or (heart attack)