| Question | Answer |
| Oxidoreductases | -catalyze redox reactions
-involve NAD,NADP,FAD as electron acceptors or donors (reduced form)
-oxidases, oxygenases, reductases, and dehydrogenases |
| Transferases | -transfer groups from one substrate to another
-transfer carboxyl, amino, glucosyl, phosphoryl and methyl
-kinases, aminotransferases, carboxylases, and methyltransferases |
| Hydrolases | -cleave bonds between atoms by addition of water
-glucosidases, ATPases, phosphatases, peptidases and lipases |
| Lyases | -break bonds between atoms without addition of water or oxidative cleavage of substrate
-usually break C-C bonds
-often contain lyase in name |
| Isomerases | -change stereochemistry of optical or geometric isomers
-mutases, epimerases or recemases |
| Ligases | -catalyze formation of bonds between carbon and other atoms
-require input of energy from ATP or others
-synthase, synthetase or carboxylase |
| Metalloenzymes | -metal containing enzymes
-metal ions with positive charge plays important role in reaction mechanism of enzyme |
| Coenzymes | -cofactors that are small organic molecules
-typically derived from vitamins
-NAD, NADP, FAD
-prosthetic group |
| Holoenzyme | -active enzyme with its prosthetic group attached
-also used to describe multimeric enzymes consisting of several subunits |
| Apoenzyme | -inactive enzyme without its prosthetic group |
| Active sites of an enzyme | -small site where enzyme binds its substrate
-often found in pocket or crevice without water |
| Induced fit model | -active sites are flexible
-binding substrate produces conformational change at active site |
| Stereospecific reactions | - allow precise active site-substrate interactions without generation of unwanted byproducts
-cannot assume R and S-enantiomers behave similarly
-50% drugs are chiral |
| Acid-Base Catalysis | -ionizable R groups of active site serve as proton donor and acceptors
-pKa of R groups tells functioning pH effective for proton donor/acceptor during catalytic cycle
-no activity at extreme pH due to denaturation |
| Covalent Catalysis | -transient formation of covalent bond between substrate and active site R groups
-unstable
-breaks down to regenerate free enzyme |
| Metal Ion Catalysis | -+ charge stabilize negatively charged intermediates
-generate nucleophile by increasing acidity of a nearby molecule (often water)
-binds to substrate, increasing number of enzyme-substrate interactions |
| Effect of temperature on Enzymes and Rx rate | -increasing the temperature to a certain point can increase the rate of the reaction
-when critical temperature is reached, interactions maintaining proper folding are overcome and denature the enzyme and catalytic activity is lost |
| Michaelis-Menten Equation | V=Vmax[S] / Km+[S]
*Vmax=max velocity
*S=substrate
*Km=k2+k3 / k1 (M-M Constant) |
| Km | -[S] at which the reaction rate is half of its maximum value
-value is independent of enzyme concentration
-approximates dissociation constant of ES complex
-low Km=tight binding
-high Km=weak binding |
| Lineweaver-Burk plot | -takes reciprocal of both sides of Michaelis-Menten equation
-gives straight line
-x intercept= -reciprocal of Km
-y intercept= reciprocal of Vmax
-1/v=Km/Vmax x 1/[S] + 1/Vmax |
| Competitive Inhibitors | -competes with substrate for binding at active site
-increase Km but not affect Vmax
-more substrate will reduce inhibition |
| Non-Competitive Inhibitors | -bind to other sites than active site
-[S] has no influence
-Vmax decreased but no change in Km |
| Irreversible Inhibitors | -chemically modify and inactivate enzyme
-bonds between enzyme and inhibitor are permanent
-Asprin |
| How can you distinguish between noncompetitive and irreversible inhibitors? | -upon removing non-competitive inhibitors, full enzymatic activity can be restored, unlike irreversible inhibitors |
| Isozymes (Isoenzymes) | -Proteins that have different amino acid sequences, but catalyze same biochemical reaction
-different isozymes are found in different tissues |
| Glucokinase and Hexokinase | -Isozymes that catalyze phosphorylation of glucose to generate glucose-6-phosphate
-Km of hexokinase for glucose is 0.1mM
-Km of glucokinase is 5mM
-hexokinase has higher affinity for glucose |
| What is the clinical importance of LDH isozyme profiles? | -by determining the composition and amount of isozyme in the serum, MI's can be detected |
| What simple step can the body take to increase enzymatic Rx rate? | -make more enzyme |
| 3D structure of isozymes of prostaglandin synthase and drug selectivity | -bad prostaglandins synthesized at site where valine residue is present (not present at good proglandin site)
-drugs can be made to selectively inhibit the bad site, but not the good site |
| Product Inhibition
give an example | -inhibition by the products of the reaction catalyzed
-phosphorylation of glucose (competition between product and substrate) |
| Allosteric modulators | -bind at sites distinct from active site
-positive or negative |
| Regulatory subunits and how they differ | -inhibitory subunits=inhibit activity of catalytic subunit
-activating subunits=sometime reuired for activation of catalytic activity, binding alters conformation
-targeting subunits=direct them to their substrate |
| Addition and removal of phosphate | -most common way to regulate enzyme activity
-binds to serine, threonine or tyrosine residue
-bulky and charged, altering conformation of enzyme
-protein kinases add Phosphate
-protein phosphatases remove |
| Zymogens and Chemotrypsin activation | -enzyme synthesized in inactive state
-activated by proteolysis
-Chemotrypsin activated by trypsin to chemotrypsinogen
-trypsin is also a zymogen, activated by enteropeptidase |
| Multienzyme complexes vs. multifunctional proteins | -Multienzyme complex= association of subunits (distinct enzymes)
-Multifunctional protein=protein folded with multiple active sites and distinct catalytic activity |
| Why is the physical association of enzymes an advantage to the cell? | -eliminates substrate diffusion/dissociation between sequential enzymatic reactions
-coordinated control of sequential enzymatic steps
-coordinated, stoichiometric gene expression of enzyme activities |
| Effect of enzymes on:
-activation energy <>
-equilibrium constant
-eq. concentrations of reactant and product
-forward and reverse rate constants - | -activation energy is decreased in both directions
-eq. concentrations of S and P is unaffected
-rate constants are increased |
| Correlation between Km and metabolic concentration due to.. - | -representing an optimal balance in sensitivity to increase and decrease on [S] |
