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Enzymes 1-2, Enzyme inhibition -control mech Types: 1. Reversible a. competitive b. non-comp 2. Irreversible Irreversible Modify enz's AA side chains or very tight binding to enz -ex-Allopurinol -inhibit Xanthine oxidase -purine breakdown to urate ->thus used to treat gout -ex-aspirin-> stop prostaglandin, thromboxane synth. -ex-organophosphates-pesticides inhibit ACh-esterase, Ser protease, Plot above eqn as 1/v vs. 1/[S] ->now linear y-int=1/Vmax x-int=-1/Km Hexokinase vs. Glucokinase glucose+ATP->G6P+ADP hexo w/ smaller Km ->more efficient at lower [gluc] -in periph tissues glucok. in liver, plenty of glucose, Enzyme inhibition -control mech Types: 1. Reversible a. competitive b. non-comp 2. Irreversible Comp. inhibitor increase Km, Vmax unchanged (decrease affinity, more substrate for same rate as before) -ex-amethoperin-Dihydrofolate reductase ->inhibit purine synthesis -very strong, used for chemotherapy -ex-EtOH for meth, ethylene glycol poisoning less toxic, compete w/ EtOH dehyd'ase -kidney stones from eth. glycol, Enzymes Trends G6P Dehydrogenase mutation -produces NADPH ->substrate of glutathione reductase -enzyme less temp-stable ->less reduced glutathione ->peroxide formation ->destabilize RBC membrane ->anemia imp't under ox. stress, prolonged fever, Michaelis-Menten Kinetics -> V=Vmax/(1+Km/[S]) [S]=Km->V=Vmax/2 Vmax=(k3)(Et) ->k3=turnover number Km, k3 constant for an enz ->indep of [S] ->temp, pH, etc.-dependent Km->substrate affinity lower Km, higher affinity Vmax at saturated substrate Lineweaver-Burk Plot Plot above eqn as 1/v vs. 1/[S] ->now linear y-int=1/Vmax x-int=-1/Km, Non-protein parts of enzyme -heme in catalase, hemoglobin Exs CoA-forms thiol esters Biotin-activate/transfer CO2 Thiamine pyrophosphate-> covalent intermed. w/ keto groups Pyridoxal phosphate-> amino transfer Alcohol dehydrogenase-> use NAD to take H2 from EtOH ->makes acetaldehyde (tachycardia, facial flushing) Acetaldehyde dehyd'ase ->makes acetate, 1. Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases Exs Chymotrypsin-Ser protease -hydrolyze peptide bonds -nucleophilic attack by Ser ->covalent acyl-enz intermed. -cleave bond in substrate -use water to dissociate enz from substrate, Enzymes Rxn Rates Michaelis-Menten Kinetics -> V=Vmax/(1+Km/[S]) [S]=Km->V=Vmax/2 Vmax=(k3)(Et) ->k3=turnover number Km, k3 constant for an enz ->indep of [S] ->temp, pH, etc.-dependent Km->substrate affinity lower Km, higher affinity Vmax at saturated substrate, Enzymes 6 types 1. Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases, Enzymes Trends Restrict motion->faster rxn rate doubles w/ 10degC increase -decreases w/ much higher temp (irreversible damage to enz)