Enzymes Flashcards
Enzyme defintion
Substance that increases rate of reaction but stays same as it was b4
Enzyme binds ______ to substrate
Reversibly
Enzyme substrate complex ______forms _______
Irreversibly
Product
Regenerates catalyst
Active sites contain
Catalytic residues
Specifiticty of enzymes involve what forces
Van der Waals
Electrostatic
H-bonding
Hydrophobic interactions
Enzyme mechanismm
Facilitates formation of transition state
Cofactors
Small molecules bound to enzyme
Enzyme with/without cofactor
Without - apoenzyme (inactive)
With - holoenzyme (active)
Two groups of cofactors
Metal ions and small organic molecules
Coenzymes
Small organic cofactors
Prosthetic groups
Coenzymes tightly bound
_____ are often precursors to coenzymes
Vitamins
V
Number of moles formed per second
Km
Concentration of S that is 1/2 of Vmax
Km measures
How tightly substrate binds
Lower Km = more tightly bound = more likely to form product
V relationship to Vmax and Km
Proportional to Vmax
Inversely proportionalto Km
Line-weaver Burke improtant points
X-intercept = 1/-Km Y-intercept = 1/Vmax Slope = Km/Vmax
Reversible inhibition types
Competitive and noncompetitive
Competitve inhibiton
Binds active site
Overcome with more substrate
Changes Km
Noncompetitive inhibition
Binds other site
Cannot be overcome with substrate
Changes Vmax
Irreversible inhibtion typically
Involves covalently bound
Can bind anywhere
Kinase
Transfer of phosphate using ATP
Phoshorylase
Adds inorganic phosphate to substrate iwhtout ATP
Phosphatase
Removes phosphatre
Dehydrogenase
Redox
Hydroxylase
Add hydroxyl
Carboxylase
Transfers CO2
Mutase
Relocates functional group within a molecule
Feedbakc inhibition
Product regulates earlier enzyme
Common in metabolism
Allosteric and how is it different than noncompetitive
Has allosteric sites that can be activated or inhibited
Sigmoidal M-M kinetics
Isozymes and example
Differ in sequence but catalyze same reaction
Allows fine-tuning
Lactate dehydrogenase
H form and M form of lactate dehydrogenase
H - Heart (higher affinity)
M - skeletal (lower)
Covalent modification (which are reversible and which are not?)
Reversible - phosphorylation, acetylation
Irreversible - attachment of lipid group that localizes protein to a membrane
Autoinhibition and example
Portion of enzyme keeps it inactive by regulatory subunits until activator binds
Protein Kinase A
Mechnaism of autoinhibition
Regulatory has pseudosubstrate sequence that binds active site of catalytic units…activator binds to regulatory sequence
Zymogens
Inactive precursors
Most undergo proteolytic cleavage to become active
Types of zymogens
Digestive enzymes
Blood clotting
Collagenase
Capsases
Aspirin common name and goup
Acetylsalicylic acid
NSAID
NSAID mechanism
Inhibit COX (cyclooxygenase enzymes)
Isoforms of COX
COX 1 and COX 2 (means it is an isoenzyme)
Aspirin targets which forms of COX?
Bot h
COX enzyme reaction
Turn arachidonic acid into PGG2…eventually forms prostaglandins and thromboxane
Prostaglandins
Make neurons more sensitive
Dilate or constrict vessels
Prevent or promotoe platelet aggregation
Aspirin…reversible or irreversible?
Irreversible…adds acetyl group
Aspirin reaction with Cox 1 and COx 2
Ser530 COX 1
Ser 516 Cox 2
Other NSAIDs bind to COX enzymes
Competitively and reversibly
Statins
Competitive inhibitors of HMG-CoA reductase
Reduce cholesterol synthesis
HMG-CoA reductase reaction and what it requires
HMG-CoA to mevalonic acid
2 NADPH
HMG-CoA reductase location and catalytic domain
Membrane protein
Cat. domain - cytosol
Statin mechanism
Binds to active site of HMG-CoA reductase and excludes HMG-CoA
