Enzymes Flashcards
What is the michaelis-menten equation?
V = (Vmax * [s]) / (Km + [s])
What is Km?
the michaelis-menten constant
- the substrate concentration at which the reaction rate is half of Vmax
What is the unit of measure for enzyme reaction rates?
μmol/min
What is specific activity?
- amount of product formed by an enzyme in a given amount of time under given conditions per milligram total protein
- more simply it is the “ratio of enzyme to non-enzyme molecules”
example:
a flask with 100 units protein and 10 units enzyme has lower spec. activity than one with 50 units protein and 6 units enzyme
What are the types of reversible enzyme inhibitors?
- competitive
- non-competitive
- un-competitive
- apparent competitive
What does a competitive inhibitor do?
How does it work when substrate is abundant?
How does it affect kinetics?
- a competitive inhibitor is a substrate analogue which binds to the active site
- does not inhibit in substrate excess
Vmax: no effect
Km: increases
ex: methanol to alcohol dehydrogenase
What does a non-competitive inhibitor do to an enzyme?
- binds away from the active site and disables enzyme
by changing the active site
Vmax: lower
Km: unchanged
How does an un-competitive inhibitor work?
How does it affect kinetics?
- binds only to the enzyme-substrate complex
Vmax: decreases
Km: also decreases
How does apparent competitive inhibition work?
How does it affect kinetics?
- the inhibitor binds to an allosteric binding site and induces a conformational change in the enzyme
- its kinetics are similar to that of competitive inhibition:
Vmax: unchanged
Km: increases
How does an allosteric activator effect an enzyme?
- binds to allosteric site and induces conformotional change which:
increases Vmax
decreases Km
How do inducers and repressors effect enyzme activity?
inducers: stimulate enyzme synthesis
repressors: inhibit enzyme synthesis
