enzyme regulation and inhibition

allosteric

activity is changed by change of 3d structure brought about by small molecules like substrates or regulators

allosteric enzymes qualities

• quaternary structure

• cooperativity between subunits

• larger than other enzymes

cooperativity of subunits

• binding by a substrate affects binding at all other subunits - becomes more active

how is rate versus [S] plot affected due to subunit cooperativity

• sigmoidal

• not hyperbolic

• at low [S] affinity is low, but more turn into high affinity

activation and inhibition of allosteric enzymes

• an allosteric enzyme has active and inactive forms

• allosteric activator can stabilise the active form (R)

• allosteric inhibitor will stabilise the inactive form (T)

PFK-1

• enzyme which catalyses fructose-6-phosphate → fructose-1,6-bisphosphate

• neg allosterically modulated by phosphoenolpyurvate and atp

• shows sigmoidal curve

hwo do allosteric regulators affect Km and Vmax

• affect Km

  • activators will have lower Km (higher affinity)

  • inhibitors will have higher Km (lower affinity)

• no Vmax

effect of constants with competitive inhibition

• km is increased

• will reach the same Vmax

effect of non competitve inhibition on constants

• vmax is decreased

• more s does not restore the rate

effect of uncompetitive inhibition on constants

• both vmax and km is decreased

• binds to enzyme-substrate complex

which inhibition is this?

competitive

which inhibition is this?

non competitive

which inhibition is this

uncompetitive