6-enzymes B Flashcards
how can you measure the rate of a chemical reaction
the appearance of product or disappearance of substrate
what remains constant under steady state condition
concentration of intermediate [ES]
what is an example reaction in enzyme kinetics
E+S - ES - E+P
what is k cat in relation to other K’s
the k constant from ES –> E + P
its the same as k2
what is k2
the k constant from ES –> E + P
its the same as kcat
what is k1
the k constant from E +S –> ES
what is k-1
the k constant from the reverse of E +S –> ES
what does total enzyme equal [E total]
[E] + [ES]
what does the Michaelis constant reflect (Km)
the balance between formation and breakdown of the ES complex
what happens to Vmax if you half the amount of enzymes
then its reduced by half too
what does [S]= if Vo=0.5Vmax
then [S]=Km
what is Vo when [S]=Km
1/2 Vmax
what does a small Km mean (2 things)
better affinity, less substrate requirted to get to max velocity
what does Kcat mean (2 words)
its the turnover number
what does the kcat constant represent
the ability of a single enzyme to catalyse product when it is saturated with substrate
what do the lineweaver-Burk plots do
generate a hyperbolic relationship between [S] and Vo - can be turned into a linear relationship
which k value does Vmax reflect
Kcat
what does specificity constant indicate
catalytic perfection
what can indicate catalytic perfection
specificity constant
what is the # range for catalytic perfection
10^8 - 10^9/Msc
what does the specificity constant mean for an enzyme
how good the enzyme is in respect to substrate, reflect specificity
what unit is specificity constant in
M-1 s-1
what do irreversible inhibitors do
covalently bind to enzymes
what do reversible inhibitors do
non-covalently associate with enzymes
what are 3 types of reversible inhibition
competitive
uncompetitive
mixed/non competitive
what do irreversible enzymes do to rate of reaction
reduce
what happens in competitive inhibition
the inhibitor resembles the substrate and competes with it for space in the active site
what does KI mean
dissociation constant
what is KI (dissociation constant) for competitive inhibition
[E][I] / [EI]
What does a competitive inhibitor do to apparent Km
increases
what is another name for apparent Km
α Km
what is another name for α Km
apparent Km
what does the α factor reflect
the number of available active sites
what does competitive inhibition do to apparent Vmax
doesnt change
what is the slope in competitive inhibition (with the 1/Vo vs 1/[S] graph)
(αKm)/(Vmax)
what happens to competitive inhibition slope with increase α (in a normal Vo vs [S] graph)
bigger α makes a less steep slope
does Km affect slope
yes
does Km affect intercept
no
what is uncompetitive inhibition
when the inhibitor binds to a site distinct from the substrate binding site AND only binds to an ES complex
what is KI’ for uncompetitive inhibition
[ES][I] / [ESI]
where do uncompetitive inhibitors bind
to ES complex
what is α’
a factor that reflects the number of effective active sites
what happens to apparent Km with uncompetitive inhibition
it will decrease
what happens to apparent Vmax in uncompetitive inhibition
it will decrease
what does apparent Km= in uncompetitive inhibition
= Km/α’
why would uncompetitive inhibitors decrease Km
because they pull ES out of the equation, so the reaction shifts toward more ES formation where it will bind more substrate to the enzymes to create more ES, which leads to a lower Km
is Vmax or Km decreased more in uncompetitive inhibition
they are decreased by the same amounts
what does Km represent (2 definitions)
a relationship between various rate constants (michaelis constant)
the balance between formation and breakdown of the ES complex
what does Km =
(K-1 + Kcat) / K1
what are the effects of uncompetitive inhibitors at higher concentrations and why
a bigger effect because there is more ES complex to be attacked
in the 1/Vo vs 1/[S] graph for uncompetitive inhibition, was is the value for slope
Km/Vmax
in the 1/Vo vs 1/[S] graph for uncompetitive inhibition, was is the value for x intercept
-α’ / Km
in the 1/Vo vs 1/[S] graph for competitive inhibition, was is the value for x intercept
1/-αKm
how do the slopes compare in uncompetitive inhibition in e 1/Vo vs 1/[S] graph (with different α’ values)
the slopes are the same
where does a mixed inhibitor bind
to a site distinct from the substrate binding site - either E alone or the ES complex
what is the K for mixed inhibition
both Ki and Ki’ are in it
what happens to apparent Vmax in mixed inhibition
it is decreased
what happens to apparent Km in mixed inhibition
it will either increase or decrease
what happens in mixed inhibition when α’=α (to Vmax and Km)
Vmax is reduced and Km is unaffected
what does apparent Km= in mixed inhibition
αKm / α’
what does apparent Vmax= in mixed inhibition
Vmax / α’
what do the relative slopes in mixed inhibition indicate
value of α
what do the relative y intercepts in mixed inhibition indicate
value of α’
what do the relative y intercepts in uncompetitive inhibition indicate
value of α’
what do the relative slopes in competitive inhibition indicate
value of α
what is apparent Vmax in competitive inhibition
keep same, Vmax
what is apparent Vmax in noncompetitive inhibition
Vmax/α’
what is apparent Vmax in uncompetitive inhibition
Vmax/α’
what is apparent Vmax in mixed inhibition
Vmax/α’
what is apparent Km in non competitive inhibition
same, Vmax
what is apparent Km in competitive inhibition
αKm
what is apparent Km in mixed inhibition
αKm/α’
what is apparent Km in uncompetitive inhibition
Km/α’
in mixed inhibition, if the intercepts of the lines are above x axis, how are α and α’ related
why
α>α’
slope is increasing faster than Km, slope is affected by α and intercept is affected by α’
in mixed inhibition, if the intercepts of the lines are at the x axis, how are α and α’ related
α=α’
in mixed inhibition, if the intercepts of the lines are below the x axis, how are α and α’ related
why
α IS FUCKING SMALLER THAN α’
