Enzymes Flashcards
Amount of product formed per unit time
Velocity
The ______is in the linear part of the M-M curve
initial velocity
At high concentration of substrate ({S}»Km) the velocity of the reaction is ______–that is constant and independent of ______
At high concentration of substrate ({S}»Km) the velocity of the reaction is zero order–that is constant and independent of substrate concentration
At low concentration of substrate ({S}<
proportional
When [S] = 0, v=
0
When [S] less than Km
v=(Vmax / (Km ) * [S]
When [S] is infinite, v=
Vmax
When [S] is equal to Km, v=
v=1/2(Vmax)
Small Km reflects a _____ affinity of enzyme for the substrate
high
Large Km reflects a _____ affinity of enzyme for the substrate
low
Michaelis-Menten kinetic analysis:
Does not require ____
pure enzyme
TO MEASURE ENZYME use
saturating amounts of
substrate (»Km)
TO MEASURE SUBSTRATE
use low substrate levels (lower or at the Km)
If there’s more enzyme (Vmax) Km (does/does not) change
does not
Also called the “turn-over” number = how many substrate molecules can be used per second
Kcat
The Kcat =
The Kcat = Vmax/the enzyme concentration
LB plot:
X intercept=
intercept=-1/Km
LB plot:
Y-intercept
1/Vmax
LB plot:
Slope
Km/Vmax
Competitive inhibitors bind to
binding site only
Noncompetitive inhibitors bind to
catalytic machinery only
Irreversible inhibitors
Kill the enzyme
Ki
inhibitor constant. Inversely related to affinity constant of the inhibitor for the enzyme.
The lower the Ki, the ____ it binds
The lower the Ki, the tighter it binds
Irreversible inhibitors
Example
Compound DIFP inhibits serine protease
Competitive inhibitors change _____, but not _____
change Km, but not Vmax
Noncompetitive inhibitors change ____, but not ____
change Vmax, but not Km
Irreversible inhibitors change ______, but not _____
Irreversible inhibitors change Vmax, but not Km
5 ways to regulate enzymes
1. Regulation by Location 2, Enzyme Zymogens 3. Protein inhibitors 4. Protein phosphorilation 5.Regulation by Substrate Levels
Example of: Regulation by Location
Enzymes in Blood Plasma: common indicator of liver damage is alanine transaminase (ALT). (A liver enzyme that balances amino acid levels). A high level is indicative of cell damage.
Example of: Protein Inhibitors
“anti-elastase” in lung tissue.
Oxidized a1-antitrypsin does not effectively inhibit elastase–>Elastase cleaves elastin–>Lung scarring & emphysema
The basic concept is that phosphorylation or dephosphorylation modifies the charge of an amino acid residue. If the serine, threonine, or tyrosine is in or near the active site of an enzyme, the enzyme activity may be changed.
Protein Phosphorylation
Changes in the substrate concentration changes enzyme activity
Regulation by Substrate Levels
Allosteric enzymes are more sensitive to substrate and (4)
- Usually contain multiple subunits
- Does not usually follow Michaelis -Menten kinetics; can define an ‘apparent’ Km
- Usually have binding sites for affector molecules
- Often regulate a reaction pathway
An allosteric enzyme is often at ______
at the beginning of a dedicated reaction pathway
Allosteric enzymes exist in ___ and ____ forms and
have binding sites for effectors
R and T forms
_____ is the inhibition of the
product of the reaction
Direct product inhibition
_______ is
typically the product inhibiting an earlier reaction
Feedback inhibition
