Allosteric Enzymes

Allosteric Enzymes

n Allosteric Enzymes

§

Change in enzyme activity by conformational changed induced by modulator binding

§

Mostly multisubunit proteins

n Modulators

§

Activators or inhibitors

§

Binding to regulatory sites

Catalytic subunit

Regulatory subunit

n Allosteric Enzymes

§

Change in enzyme activity by conformational changed induced by modulator binding

§

Mostly multisubunit proteins

n Modulators

§

Activators or inhibitors

§

Binding to regulatory sites

Allosteric inhibitor

(PEP)

Allosteric inhibitor

Arginine

Competitive inhibition

Competing each other for enzyme binding

Increase in K_m

No change in V_m(why?)

Competitive inhibition

Competitive inhibition

Derive the equation for enzyme kinetics with competitive inhibition using pseudo-steady state hypothesis (PSSH).

n V_o =V_max [S] / (aK_m + [S])

§ a = 1 + [I] / K

_I

§ ^{a > 1}

§ a = 1 : no inhibition

n Increase in apparent K_m by a (decrease in substrate affinity) n No change in V_max

Competitive inhibition

Lineweaver-Burk Plot

n V_o =V_max [S] / (aK_m + [S])

§ a = 1 + [I] / K

_I

§ ^{a > 1}

§ a = 1 : no inhibition

n Increase in apparent K_m by a (decrease in substrate affinity) n No change in V_max

Uncompetitive inhibition

§

Inhibitor binds only to ES complex at a site distinct from the active site

§

Decrease in V_max (∵V_max → V_max / a’)

§

Decrease in apparent K_m (∵ K_m → K_m / a’)

§

Inhibitor binds only to ES complex at a site distinct from the active site

§

Decrease in V_max (∵V_max → V_max / a’)

§

Decrease in apparent K_m (∵ K_m → K_m / a’)

Slope =V_max/K_m

1/V_max

Uncompetitive inhibition

Derive the equation for enzyme kinetics with

uncompetitive inhibition using equilibrium constants.

n Inhibitor binds to either E or ES at a site distinct from the active site n Decrease in V_max by a

n a = 1 + [I] / K_I

n No change in K_m : Inhibitor binding does not affect affinity of substrate to active site

Noncompetitive inhibition

Noncompetitive inhibition

H.W.

Derive the equation for enzyme kinetics with noncompetitive inhibition using equilibrium constants.

H.W.

Derive the equation for enzyme kinetics with

noncompetitive inhibition using equilibrium

constants.

Enzyme Activity Depends on pH

n pH affects enzyme activity

§

Charge of active site functional group is pH-dependent

§

Tertiary structure of enzyme is pH-dependent n pH affects enzyme activity

§

Charge of active site functional group is pH-dependent

§

Tertiary structure of enzyme is pH-dependent

+ H⁺

How to derive this equation? Refer to textbook, page 75~76

pH = -log[H⁺]

Enzyme Activity Depends on Temperature