FBICH 410 1st Edition Lecture 22Outline of Last Lecture - Enzymes ChemistryOutline of Current Lecture - Catalytic Mechanismso 3 types: acid base, covalent, metal ion catalysiso Acid Base Catalysis- proton transfer General acid catalysis- acid donates proton to substrate- Enzyme active site residue must be protonated General base catalysis- base accepts proton from S- Enzyme active site residue must be deprotonated Concerted acid-base catalysis- general acid and base so both participate in rxn Enzyme activity as function of Ph- General base has highest activity when group deprot. Ph>pka B +H+- General acid has highest activity when group prot. Ph<pka AH- Concerted rxn has highest activity at both deprot and prot region- bell shapecurve for pH dependence Covalent catalysis- covalent bond transiently formed between S an enzyme- Usually involves nucleophile on enzyme and electrophile of S- Nucleopphiles- nucleophilicity of substance is related to basicityo Nucleophiles are – charged or have shared e-- Electrophiles- electro + or contain unfilled valence electron shells or have electro + atoms- The more electrophilic S the weaker the nucleophile can be Metal Ion Catalysis- - Nearly 1/3 enzymes require metal for activity- Melloenzymes- contain tightly bound metal cofactors- Fe, Cu, Zno Bound Metal required for activity- Metal activated enzyme- loosely bound metal ions usually Na, K, Cao Metal ion is used for stability not for activity- Cofactor- metal ion- Coenzyme/cosubstrate- organic molec NAD- Apo- inactive from of enzyme when it lacks the cofactor- Halo- active form of enzyme with cofactor Examples of determining catalytic mechanism- need to know chemical and kinetic mechanismThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Ribonucleus A- chemical mechanism= acid base catalysis; uses hydrolase; kinetic mechanism= ping pong- Carbonic anhydrase- H20 interacts with Zn and pH decrease chemical mechanism= metal ion- Serine proteases- proteolytic enzymes that have a serine active siteo Ie chymotrypsin, subtillsin, thrombin(blood clotting), trypsin, elastase, plasmin (breaks down clots), tissue plasminogen activator (cleaves plasminogen creating plasmin)o Selectivity pocketo Mechanism of serine proteases- catalytic triad: His, Asp, Ser Active sites of trypsin, chymotrypsin, elastase have triad Asp form H bond to His orienting His so it can have electron pair exposed to bind Ser Chymotrypsin hydrolase – peptide +h20 2peptides Mechanism involves acylation and deacylation rather than direct h20 attack Uses presteady state analysis Chemical Mechanism: Acid base and covalent catalysis; kinetic mechanism: ping pong initial velocity plot has parallel lines- Transition State stabilization- tetrahedral intermediateo Serine proteases are examples of enzymes that preferentially bind transition stateo Tighter an enzyme binds the transitions tate the greater the Kcat to Kuncat- Nerve toxins- o acetylcholinterase- works same as trypsin Serine esterase and neurotransmitter Nerves are repolarized upon hydrolysis of
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