Enzyme Kinetics

define enzyme kinetics

study of the enzymatic rct rate

define the Ks.

k₁ = formation of ES (enzyme-substrate complex)

k_-1 = breakdown of ES (enzyme-substrate complex)

k₂ = formation of P (product)

k_-2 = breakdown of P (product)

what is the steady state assumption

ES formation rate = ES breakdown rate

define this [E_T] = [ES] + [E]

total amount of enzyme = enzyme binded to the substrate and the free enzyme

when K_s is small, what does it mean for the affinity of E to S? When K_s is large, what does it mean for the affinity of E to S?

K_s is small » good affinity of the E to S

K_s is large » less affinity of the E to S

define rate constant (k)

expresses the relationship btwn the chem rct rate and the concentration of the reactants

k₁([E_T]-[ES])[S] = k_-1[ES] + k₂[ES]

formation of ES rate

breakdown of ES rate

define K_M

the [S] at which the rct rate is at half-max

define the top term and bottom term

top: breakdown of ES

bottom: formation of ES

define V_max

when [S] is high and the enzyme is saturated / or no more available enzyme for the substrate to bind to

define K_s

dissociation constant of the Michaelis complex

when the K_M and K_s goes down, how does that affect the enzyme’s affinity for the substrate?

makes the affinity stronger or increases it

define k_cat

catalytic constant aka turnover #: # of rct process that the enzyme catalyzes per unit time

what is an inhibitor

substances that reduce an enzyme’s activity by influencing the binding of substrate and enzyme’s turnover #, and structurally resembles the substrate

what is an inactivator

inhibitor, but the process of inhibition is irreversible

is the process of inhibition by a inhibitor reversible?

yes, it is common

what are the types of E inhibition?

competitive, uncompetitive, and noncompetitive/mixed

what does comp. inhibition do?

the inhibitor competes w the S for the enzyme’s binding site and reduces the [ ] of free E avail. for substrate binding

what kind of inhibition is this?

comp. inhibition

what kind of inhibition is this?

competitive inhibition

what inhibition is this

comp inhibition

what does the uncomp inhibition do

the inhibitor binds to the enzyme-substrate complex and distorts the active site thereby rendering the E catalytically inactive

T/F - adding more substrate does reverse the effect of an uncomp inhibitor b/c S binding does interfere w uncomp inhibitor binding

F - adding more S doesnt interfere w the process of uncomp inhibition

what is noncomp./mixed inhibition

inhibitor binds to the enzyme site whether or not it has substrate bind to it

what inhibition is this

noncomp/mixed

when there is comp inhibition what is the effect of it on the michaelis-menten rxn?

increases K_M

when there is uncomp inhibition what is the effect of it on the michaelis-menten rxn?

decreases K_M and V_Max

when there is noncomp/mixed inhibition what is the effect of it on the michaelis-menten rxn?

decreases V_max and may increase or decrease K_M

what inhibition is this

comp inhibit

what inhibition is this

uncomp inhibit

what inhibition is this

noncomp/mixed inhibition

T/F - Organisms need to control their catalytic activities to coordinate metabolism, respond to environmental changes, grow and differentiate.

True

what are ways to control enzyme’s activity?

1) feedback or product inhibition

2) substrate availability

3) amount of enzymes

4) covalent modifications

5) allosteric interactions

6) specialized control

7) modulators

what is covalent mod?

changes configuration; some common ones are phosphorylation/dephosphorylation

what is allosteric interactions

a modulator binds to another site besides the active site and changes the E conformation

what is feedback inhibition

when a product of metabolism inhibits its own synthetic pathway in an earlier step

what type of way of controlling enzyme activity is this

feedback inhibition

what is product inhibition

the product of the enzyme reaction inhibits the activity of the enzyme that produced it

what are some kinds of specialized controls

zymogens, isozymes, and modulators

what are zymogens

inactive enzymes that need to be activated

what kind of specialized control is this

zymogens

what is isozymes

made up of more than 1 peptide subunit

what are modulators

bound proteins on enzymes added or removed to affect E activity

what kind of specialized control is this

modulator

what is homoallostery

cooperative substrate binding and inhibition

what is heteroallostery regulated by

regulated by heterotropic allosteric effector molecules

T/F - An E’s activity can be affected by the binding of a molecule at a site other than the active site

T

what is ATCase (aspartate carbamoyltransferase), the enzyme, inhibited by? is it on the active site or allosteric site?

CTP (cytidine triphosphate), a pyrimidine nucleotide at the allosteric site

what is ATCase (aspartate carbamoyltransferase), the enzyme, activated by? is it on the active site or allosteric site?

ATP (adenosine triphosphate), a purine nucleotide at the allosteric site

what does ligand binding-induce in allosteric regulation

conformational changes by the rapid association or dissociation of the ligand and the [ligand] acting as a signal that cell needs more or less product

what does allosteric activator do in terms of activity

higher activity

what does allosteric inhibitor do in terms of activity

lower activity

who is the homotropic effector when there is allosteric activation

substrate itself

who is the heterotropic effector in allosteric activation

metabolite in pathway (feed ahead activation) or other ligand indicating need

who is the heterotropic effector in allosteric inhibition

product of pathway (feedback inhibition) or some other ligand indicating a need for less pathway product

what does R state indicate about the binding, affinity, and kind of allosteric regulation

prefers to bind to enzyme’s active site, high affinity, and it is a heterotrophic activator

what does T state indicate about the binding, affinity, and kind of allosteric regulation

prefers to bind to enzyme’s inactive site, low affinity, and it is a heterotrophic inhibitor