2.5 Regulation of Enzyme Activity Flashcards
feedback inhibition competitive, noncompetitive, and mixed inhibition uncompetitive inhibition allosteric enzymes, covalently modified enzymes, zymogens
feedback inhibition
“negative feedback”
when an enzyme is inhibited by high levels of a product later on in its pathway
(once we have enough of a given product, we want to turn off the pathway that created that product)
competitive inhibitor
bind to the active site of the enzyme to block substrate binding
competitive inhibition (km and vmax effects)
km is increased (lower affinity for substrate)
vmax is unaffacted
non competitive inhibitor
binds to an allosteric site to alter the active site so the substrate can no long binder
noncompetitive inhibition (km and vmax effect)
Km is unaffected
vmax is reduced
uncompetitive inhibitor
bind to the enzyme-substrate complex (not the free enzyme)
uncompetitive inhibition (km and vmax effects)
km is decreased (they increase binding affinity because it stabilizes the ES complex)
vmax is decreased
mixed inhibition
an inhibitor which can bind to either the enzyme or the enzyme-substrate complex, but has different affinities for each
bind at allosteric site (just like a noncomp. inh.)
mixed inhibitors (Km effect)
increases if inhibitor prefers to bind to enzyme alone
decreases if inhibitor prefers to bind to ES complex
mixed inhibitor (vmax effect)
vmax is decreased
suicide inhibitor
A substrate analogue that binds IRREVSERIBLY to the active site via a covalent bond
allosteric effector
bind at the allosteric site and induces a change in active site conformation
can either activate or inhibit enzymes
V max unchanged
Km increased
homotropic effector
An allosteric regulator that is ALSO the substrate
heterotropic effector
An allosteric regulator molecule that is DIFFERENT from the substrate
methods that can be used to activate or deactivate enzymes
phosphorylation or dephosphorylation (attachment or removal of phosphate)
glycosylation (attachement of sugars)
