Biochem Module 8: Enzyme Kinetics

what is Keq known as

the equilibrium constant between substrates and reactants

Keq formula

Keq= [P][Q]/[A][B[

gibbs free energy formula

Delta G= Delta G of the products- Delta G of the substrates

Delta G0

the change in free energy when 1 molar concentration of substrate and products comes to equilibrium

Delta G0’

the change in free energy at equilibrium AND at a Ph of 7.0. standardizes conditions

-Delta G value

the reaction is favored to the right and is spontaneous and exergonic. the products have less energy than the reactants

+Delta G value

the reaction is favored to the left and is endergonic. The products have more energy than the reactants

Relationship between Delta G and Keq

Delta G= -R _{(gas constant)}T_{(absolute temp in Kelvin)} ln Keq

Delta Gf

the activation energy, usually positive and is an energy barrier to overcome to go from substrate to products

kinetic order depends on what

the molar ratios of the reactants

A+A → P

what is the order with respect to A

second order

A + B → P

what is the order in all respects

to A, first

to B, first

to A and B, second

Enzymes ____ affect the Keq

do not

Enzyme assays usually measure

Initial Velocity V0

Why does V0 represent enzyme concentration

it is the rate of the forward reaction since the reverse reaction is negligible at the start. it is pseudo first order with respect to the enzyme

what affects the reaction rate in Enzyme kinetics

the substrate concentration

what are the x and y axis in a reaction rate graph

x- substrate concentration

y- reaction velocity

vmax

maximum velocity the reaction can reach, substrate concentration dependent

Km

substrate concentration where the velocity is half of the Vmax

Michaelis Menton equation

V0= Vmax [S]/ Km + [S]

Whenb [S] < Km, the V0 is…

directly proportional to [S], it is a straight line

3 types of double recirpocal plots

lineweaver burke, eadie hofstee, and hanes-woolf

formula for lineweaver burk double reciprocal plot

1/V0= Km/Wmax* 1/[S]+ 1/Vmax

where do competitiive inhibitors bind

the active site

where do noncompetitive inhibitors bind

somewhere that allosterically influences the enzyme’s rate

the ___ approximates the affinity of the enzyme for its substrate

Km

a low Km indicates

high enzyme affinity for the substrate/inhibitor

how are vmax and km of the substrate affected in competitive inhibition

-vmax stays the same

-km for S increases

how are vmax and km of the substrate affected in noncompetitive inhibition

-vmax decreases

-km stays the same

uncompetitve inhibition

the inhibitor only binds to the enzyme-substrate intermediate

how are the vmax and km affected with uncompetitive inhibition

vmax- decreases

km- decreases

in what instances can MM kinetics not be used to evaluate enzyme kinetics

-tightly bounbd inhibitors (irreversible)

-mechanism based suicide inhibitors

how do you evaluate multi-substrate enzymes with cooperative binding

HILL equation

HILL equation

log V0/(Vmax-V0) = nlog[S]-log K’

HILL coefficient

slope n, reflects the number, nature, and stregth of the interactions of the substrate binding sites

Sequential of single displacement reactions

both substrates form a ternary complex with the enzyme. can be ordered or random, but ternary complexes are associated with random

ping pong reaction

binds 1 substrate at a time

what is the effect of increaseing S2 on the rate of the reaction S1

km increases ???