enzyme kinetics and inhibition Flashcards
kinetics
study of the rate at which some process progresses
equilibrium assumption
assuming P is produced more slowly that ES is dissociated, so that k2«k1, the rate of ES formation reaches equilibrium relatively rapidly
steady-state assumption
assuming the probability the P->S is very low, k2 can be ignored. therefore, the reaction reaches a steady state in which the rate of ES formation equals the state of ES loss, either to reverse reaction or product formation
what is the equation for enzyme kinetics?
E+S <->ES<-> E+P
at low [S], most of the enzyme is in the unbound form, E; what does the initial reaction velocity do?
increases linearly with [S], since the formation of [ES] depends on [S]
at high [S], most of the enzyme is in the ES complex; the initial velocity no longer increases linearly with substrate concentrations and …
approaches a maximum Vmax, since [ES] no longer depends on [S]
total enzyme concentration
[Et]=[E]+[ES]
michaelis constant
Km= (k-1+k2)/k1
what is kcat?
limiting rate constant for a general catalysis reaction so for this simple reaction, kcat=k2
what does Vmax equal?
Vmax=kcat[Et]
what is the michaelis-menten equation?
Vo=Vmax[S]/km+[S]
Km
substrate concentration that gives a rate, Vo, equal to Vmax/2
what is Kd?
k-1/k1
what is Vmax?
maximal or saturating rate that an enzyme-catalyzed reaction approaches at high substrate concentrations
when [S]»Km, Vo=
Vmax[S]/[S]=Vmax
kcat is the turnover number meaning?
maximum number of substrate molecules an enzyme molecule can convert to product per unit time
kcat equal what?
Vmax/[Et]
kcat/Km
can be used as a specificity constant because it is a measure of the enzyme’s catalytic efficiency
the larger the kcat/km, the better the what?
the catalytic efficiency
kcat/km has an upper bound of …
10^8 to 10^9 1/M*s, because ES formation is limited by rate at which E and S can diffuse together
the rate of chymotrypsin-catalyzed peptide bond cleavage exhibits a…
bell-shaped pH dependent profile
enzyme activity can be inhibited by small molecules and other proteins, which bind to the enzyme, but do not produce a product, which is what?
noncovalent (or reversible) inhibition, covalent (or irreversible) inhibition
competitive inhibition (reversible) equation
Vo= Vmax[S]/(1+[l]/Ki)Km+[S]
uncompetitive inhibition (reversible)
a’/Vmax
