Enzyme kinetics and inhibition Flashcards
what is enzyme kinetics used for?
to determine quantitative relationships
what is a progress curve used for?
to measure product formation as a function of time
why does the slope of a progress curve begin by being linear and the gradually decrease?
because of product inhibition or enzyme inactivation
what do rate equations do?
describe chemical processes
what is the rate equation for a unimolecular reaction? bimolecular?
v=K[A]
v=K[A][B]
what with the rate of product formation generally increase with?
the amount of enzyme present
what is the michaelis-menten equation?
v=vmax[S]/Km+[S]
what is vmax?
where the reaction velocity reaches its plateau
what does reaction rate depend on?
[ES]
what does Km =?
K-1 + K2/K1
what indicates catalytic efficiency?
Kcat/Km
what does Kcat indicate?
how fast an enzyme can act, the number of catalytic cycles that each active site undergoes per time
what does Kcat=?
vmax/[E]total
for the simplest enzyme pathway what does Kcat =?
K2
what does a high affinity for substrate do to the progress curve?
pushes it left
on a progress curve at Vmax/2 what is Km?
Km = [S]
what is Km?
substrate affinity
what is catalytic perfection?
when the enzymes rate is completely controlled by diffusion
Kcat/Km = 10^8-10^9
what does a lineweaver-burk plot accomplish?
it linearizes michaelis-menten data
plots 1/V vs 1/[S]
what does a lineweaver-burk plot give?
a negative slope, yintercept = 1/vmax, xintercept=-1/Km
what two types of enzyme inhibition are there?
reversible or irreversible
what is irreversible enzyme inhibition?
molecules that covalently modify the active site
what is a transition state analog?
something that is often a better inhibitor than substrate analogs because they lower the ∆G
what are reversible inhibitors?
normally bind to enzymes non-covalently and can be classified by where the bind and what reaction steps they block; these are kinetically distinguishable
what are some different types of reversible inhibitors? (4)
competitive, non-competitive, uncompetitive, mixed
what is a competitive inhibitor?
it binds at the active site so it competes with the substrate, depends on the [S] vs [I], mutually exclusive with the substrate
what does a competitive inhibitor appear to increase? Vmax?
Km
no change
what way does a competitive inhibitor push the M-M plot?
right, makes the L-B plots slope steeper
what is a noncompetitive inhibitor?
substrate and the inhibitor are not mutually exclusive bust the ESI complex is less active than the ES complex
there are separate binding sites on the enzyme
non-competitive inhibitors effect on Km and Vmax? M-M plot?
decreases Vmax, no change to Km
M-M plot pushed down
whats an allosteric enzyme?
often have multiple subunits and show cooperativity: the subunits interact to give a sigmoidal curve instead of a hyperbolic one (M-M plot), thus they do not easily fit the M-M model.
how do allosteric effectors inhibit or activate?
inhibit using a pathway end product activate by a co-substrate, often involves an early or/and a committed step in a metabolic pathway
