ENZYME PART 2 Flashcards
Catalytic mechanisms
Acid-base catalysis
Nucleophilic catalysis
Elctrophilic catalysis
Catalysis by proximity and orientation
Preferential transition state binding
Acid-base catalysis
Proton donation and acceptor
Histidine
Nucleophilic catalysis
Nucleophile (enzyme)
Electrophile (substrate)
Promote substitution reaction
Serine Proteases: Catalytic Triad
Ser His Asp
Ser
Nucleophile; Nucleophilic catalyst
Form covalent bond
His
Acid base catalyst
Asp
Stabilizes histidine
Electrophilic catalysis
Nucleophile: Substrate
Electrophile: Enzyme
Elimination
Electrostatic Catalysis
Binding substrate excludes H2O from the active site
Local dielectric constant active site resembles that in an organic solvent
Ionic interactions
Catalysis by proximity and orientation
Enzyme attract substrate in certain orientation to react with cosubstrate
Preferential transition state binding
Transition state has higher binding affinity than the substrate
Regulation of activity
Coordination of numerous metabolic processes in the cell
Respond to changes in its environment
Grow and differentiate all in an orderly manner
Enzyme types based on regulation
Constitutive
Inducible
Constitutive
Produced all the time
Healthy state or normal state
Inducible
Produced only when needed or in the presence of substrate
Regulatory mechanisms
Feed forward
Positive feedback
Negatuve feedback
Up regulation
Down regulation
Allosteric regulation
Allosteric site
Any part of the enzyme but not active site
Alters the acitivity of the enzyme
Monod, Wyman, Chageux (MWC) Model
Symmetrical model
One step activation or deactivation
Koshland, Nemethy, Filmer (KNF) Model
One subunit is active and the other one is not
Two step activation
Regulation by covalent modification
Protein kinase - activate the enzyme
Protein phosphatase - deactivate the enzyme
Regulation by modular proteins
Convert inactive enzyme into active enzyme
Promotes the phosphorylation of other protein or other enzymes
Factors affecting enzymatic activity
Temp.
pH
Substrate conc
Michelis-Menten Model
Applies only to enzymes that dont have multiple binding sites and whose Km is higher than the total enzyme concentration
Km
Substrate conc at Vmax/2
[E][S]/[ES]
Linewaever-Burk Plot
1/Vo=(Km/Vmax)1/[S] + 1/Vmax
Enzymes are highly efficient
10^3 - 10^8 times faster than uncatalyzed reactions
Product turnover per enzyme molecule
100-1000/sec
Kcat=Vmax/[E]T
Number of processes that each active site catalyzes per unit of time
Kcat/Km
Measure of the catalytic efficiency of the enzyme
Measuring reaction velocity
V=delta[P]/delta[Time] or delta[S]
Competitive inhibitors
Binds in free enzymes to form EI
same Vmax
High Km
High slope
Uncompetitive Inhibitors
Binds ES complex to form ESI
Low Vmax
Low Km
Same slope
Mixed Inhibitors
Binds free enzyme and ES complex
Low Vmax
High Km
High slope
Mixed Noncompetitive
Binds free enzyme allosteric to form EI
Low Vmax
Same Km
High slope
Enzymes as drugs
Oncolytic agents
Anticoagulant
Enzyme replacement therapy
Oncolytic agents
L-asparagine
Neuraminidase
Anticoagulant
Tissue plasmin activator
Streptokinase
Enzyme replacement therapy (ERT)
Collagenase
Papain
Trypsin and chymotripsin
Enzymes used in clinical diagnosis
Present in highest conc
Present at low level
Used as reagent
Enzymes present in highest concentration
Has systemic functional role
Thrombin in blood coagulation
Enzymes present at low level
No systemic functional role
Indicators of disease of organs and tissues
Enzymes used as reagent
Creatinase, cholesterol oxidase, glucose peroxidase
