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36 Cards in this Set

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What two things do enzymes do?
1) speed up slow reactions
2) catalyze otherwise impossible reactions
What binds a small molecule to a Protein?
-H-bonds
-Ionic bonds
-Hydrophobic interaction
-Van der Waals forces
(very sensitive to interatomic distance)
What are 6 classes of enzymes?
1) oxidoreductases
2) transferases
3) hydrolases
4) lyases
5) Isomerases
6) Ligases
What reaction type is: oxidoreductases?
-Oxidation-Reduction
ex; Lactate Dehydrogenase
What reaction type is: Transferases?
-Group Transfer
ex; nucleoside monophosphate kinase (NMP Kinase)
What reaction type is: Hydrolases?
Hydrolysis
ex; Chymotrypsin
What reaction type is: Lyases?
Addition or removal of groups to form double bonds
ex; fumarase
What reaction type is: Isomerases?
-Intramolecular group transfer
ex; Triose phosphate isomerase
What reaction type is: Ligases
-Ligation of two substrates at the expense of ATP
ex; Aminoacyl-tRNA synthetase
What does alcholol dehydrogenase do?
-Catalyze the reduction of Acetaldehyde to ethanol
-Systematic name is EC 1.1.1.1
What does NMP kinase do?
-It transfers a phosphoryl group from ATP to NMP to form NDP, hence it is a transferase-group 2
How do you calculate velocity for a linear plot of kinetic data?
What is this called?
Vo= (Vmax[S])/(Km + [S]
OR 1/Vo= (Km/Vmax)x(1/[S])+(1/Vmax)
*Called the Michaelis-Menton Equation
What is the name of the plot one would use for a Uni-Uni enzyme?
-double reciprocal plot OR
-Lineweaver-Burk Plot
What are 5 reasons for finding Km?
-Km comparisons
-different substrates
-Ligand induced changes in Km
-intracellular [S]
-Enzyme assay
What is Aspariginase used for?
What variation is there?
-Leukemia treatment
-aspariginases with high or low Km's were ineffective
Where is hexokinase found?
-In the muscles of man and animals
-also in the liver (along with glucokinase
What is the main difference between hexokinase and glucokinase in terms of what they use?
-hexokinase (low Km of 37uM)will work with many hexoses, whereas glucokinase only uses glucose (high Km of 10mM)
How does hexokinase work in muscle?
-works as fast as it can, near Vmax
-any glucose or hexose taken up by muscle is phosphorylated and locked into the muscle
How does hexokinase work in the liver?
-hexokinase can not respond to blood glucose increase, but it can work with glucose in the liver for catabolic needs (of liver)
-after a meal, liver imports more glucose to store as glycogen
Where is lactate dehydrogenase found?
-in muscles (and therefor the heart)
How does muscle LDH work?
-muscle LDH has a high Km for pyruvate. As pyruvate increases, more lactate is formed and fatigue results
How does heart LDH work?
-since heart shouldn't get fatigued, LDH has a low Km for pyruvate in the heart:
-can't respond to increased pyruvate
-high pyruvate completely inhibits LDH in heart
What are enzyme inhibitors used for?
-establish nature of reactants
-establish nature of binding sites
-stablish the specificity of the enzyme
-determine the reaction mechanism
What is the basis for rational pharmacology and chemotherapy?
-Drugs work as selective inhibitors by natural (or synthetic) compounds
-Inhibition of enzymes lies at the root of the mode of action of many drugs
What are the two classes of inhibitor classes?
-reversible
-irreversible
What happens to Vmax and Km in an irreversible inhibitor reacton?
Vmax goes down and Km is unchanged
What affect do heavy metals have on proteins?
-since this is in the inhibitor section, it inhibits it!
-to be precise, metals inactivate proteins
What is a benefit of irreversible inhibitors?
-can identify imprtant groups in the enzyme
What is an example of how an irreversible inhibitor is used?
-Iodoacetate treatment of RNAase at pH 5.5 inactivates an enzyme
-Look for alkylation on His 12 or 119
-If there, these histidines are important in the active site of the enzyme
What is Acetylcholine Esterase?
-an enzymatic catalyst that is the site of action of organophosphate nerve gasses
How does a competitive inhibitor work?
-When inhibitor is added, reaction is pulled to the left, increasing Km (dissociation constant)
-If you add enough S to push all the enzymes to ES, you can get product still and Vmax is unchanged
What are the different types of reversible enzyme inhibitors?
-competetive
-nonclassical competitive
-uncompetetive
-noncompetitive
Where do the lines intersect for each type of reversible inhibitor
-Competative: Y-axis
-uncompetitive: parallel
-noncompetative: X-axis
-mixed/nonclassical: intersect anywhere but the x or y axis
How does a Noncompetitive inhibitor work?
-no effect on binding of S so Km is unchanged
-can not force all of enzyme to ES, so Vmax is decreased
How does an Uncompetitive Inhibitor work?
-Pulls equation to the right, so Km decreases
-Can not drive all enzyme to ES, so Vmax decreases
How does a mixed type inhibitor work?
-effects binding site, so Km increased
-If I is present, you will always have ESI, hence Vmax decreased