Enzyme Kinetics

enzymes greatly accelerate the rate of reaction factors of

10³ to 10^(20)

enzymatic reactions can occur under physiological conditions in which

they could not normally occur

Enzymes will not induce a reaction that is

unfavorable due to a positive free energy change

enzymes have a high specificity for the

reaction substrate

high reaction specificity is defined as

chemical reactions typically have a problem with unwanted contaiminating side reactions but this does not occur in enzyme ctalayzed reactions

Enzymes are

unchanged in the reactions and can undergo rapid turnover

Enzymes frequently are subject to regulation to alter their

substrate binding afinity or acitivity

the largest class of enzymes are

proteins

Other class of enzymes are

ribozymes

RNA was the

first enzyme

Oxioreductase

example of oxireducatase family enzyme

alc dehydrogenase

transferase class

hydrolases class

lyases class

isomerases class

Ligases class

The first step in the enzymatic reaction

E + S = ES

the slow or rate-limiting step in the reaction is

The first step in the reaction, E + S ES; the substrate must find the enzyme in the solvent; this rate is dependent on the concentration of the substrate and is limited by the diffusion rate.

first enzymatic step in the reaction is

reversible

K_1

formation of ES complex

F_-1

dissociation complex

The second step occurs very

rapidly

the second step is considered

irreversible

The progress of a biochemical reaction is

dependent on the free energy changes as the reaction proceeds

The rate of an uncatlyzed reaction is tied to the size of the

activation energy

Enzymes lower the

activation free enrgy needed to get to the transition state which increases the forward rate constant

Michaelis -menten kinetics are used to study enzymes at

steady-state

At VMAX the enzyme is

working as fast as it can

The vmax of an enzyme is determined by its

catalytic constant Kcat and its concentration

Km is defined by the ratio of

rate constants that dissociate and associate the substrate

when K2 is small relative to K-1 the Km value is

close to the dissociation constant between the substrate and the enzyme

The strength of the enzyme is determined by Kcat and Km

Kcat and Km

kcat

turnover number

Kcat Turnover

indicates how fast the enzyme can work under conditions in which there is saturating amount of substrate; a strong enzyme will have a large kcat value.

the enzymatic rate constant is

Kcat/Km

Diffusion-controlled limit

the limit to rate constants caused by ES complex forming due to diffusion

The diffusion-controlled limit determines how

small the Km value can be

Lineweaver-burk

michaelis-menton equation transofmred to a linear graph

An enzyme that is allosteric will exhibit

velocity curves that depend a lot on whether activator or inhibitor effectors are present

An allosteric activator

is a ligand that increases the activity of the enzyme.

an allosteric inhibitor is a

ligand that decreases the activity of the enzyme