Lecture 13 Flashcards
Km
Michaelis Constant
[S] where reaction rate is half maximal or half the active sites are full
v max
maximum velocity
maximum rate possible for a given concentration of enzyme
k cat
Turnover number
number of substrate molecules converted per active site per time (first order rate constant)
Ks
dissociation constant of substrate binding
K cat / Km
specificity constant
measure of enzyme performance by predicting fate of E*S
Michaelis-Menten Equation
E+S+E*S->E+P
enzyme follows this model
Michaelis-Menten Enzyme
1st order enzyme
no cooperativity of binding sites
Zero Order Reaction
If [S] vs. time is linear, then the reaction is 0-order
v = k[S]* = k
First Order Reaction
If ln[S] vs. time is linear, then the reaction is 1-order
v = k[S]^ = k[S]
Second Order Reaction
If 1/[S] vs time is linear, then the reaction is 2-order
v = k[S]^2
Assumptions of the Michaelis-Menten equation/model
- binding of the substrate is at equilibrium
- Since we are measuring initial rate, not enough product is present for the reverse reaction to occur. (second step is irreversible)
- Steady State Assumption: when [S] is very large, deltaS=0; formation of E*S occurs at the same rate as its loss.
A good enzyme has kcat__K-1.
A bad enzyme has kcat__K-1.
> > E*S goes to products
«_space;
E*S dissociates
Lineweaver-Burke Plot
double reciprocal plot
allows you to make linear plot of experimental data and determine important MM model values
each data point on LWB plot summarizes an individual kinetic assay
Competitive Inhibition LWB Plot
Lines all cross on y-axis at 1/vmax
Km is variable
Vmax is constant
Noncompetitive Inhibition LWB Plot
Lines meet at x-axis -1/Km
Km is constant
Vmax is variable
