Lesson 11: Enzyme Kinetics

kinetics

study of rates of reactions

k

rate constant

first order reaction

single reactant --> single product

k units in first order reaction

time^-1

first order rate equation

V = k[A]

second order reaction

2 reactants --> single product

k units in second order reaction

(time^-1)*(concentration^-1)

second order rate equation

V = k[A][B]

enzyme reaction type (# order, and why)

first order, because enzyme is constant (not used up)

Vo, depends on

initial velocity of a reaction, depends on [S]

how to measure Vo

plot produce vs time

shape of V vs [S] for enzymes and why

hyperbolic; at low [S], V 𝛼 [S], but at high [S], V plateaus at Vmax --> enzymes are saturated

Michaelis-Menten kinetics

theory of enzyme kinetics based on E + S

Briggs & Haldane assumptions

Steady-State Assumption and Initial Velocity Assumption

Steady-State Assumption

assume [ES] reaches a steady state quickly; ES is formed at the same rate it dissociates to form product

Intitial Velocity Assumption

assume [P] is negligible early in reaction --> Vo is independent of back reaction E + P --> ES

Michaelis-Menten Equation

Vo = (Vmax * [S])/(Km + [S])

Km (definition)

Michaelis constant; ratio of rates of dissociation to association, constant value for a given enzyme & substrate pair

Km (equation)

Km = (k-1' * k2)/k1

Vmax

velocity of reaction when enzyme is fully saturated

[S] at 0.5Vmax

Km

Lineweaver-Burk Plot

converts hyperbolic to linear plot using double reciprocal

slope of Lineweaver-Burk Plot

Km/Vmax

x-axis of Lineweaver-Burk Plot

1/[S]

y-axis of Lineweaver-Burk Plot

1/Vo

x-intercept of Lineweaver-Burk Plot

1/Vmax

y-intercept of Lineweaver-Burk Plot

1/Vmax

enzyme kinetic constants

numerical parameters that measure how fast an enzyme works nad how well it binds its substrate

Kcat (name and definition)

turnover number; rate of catalysis at full saturation

Kcat (equation)

Kcat = Vmax/[Et]

Kcat units

time^-1

specificity constant

Kcat/Km; measure of catalytic efficiency -> can compare different enzyme-substrate pairs