Many enzymes do not demonstrate hyperbolic saturation kinetics, or typical Michaelis-Menten kinetics. Graphs of initial velocity vs. substrate demonstrate sigmoidal dependency of v on S, much as we discussed with hemoglobin binding of dioxygen. Enzymes that display this non Michaelis-Menten behavior have common characteristics. They
are multi-subunit
bind other ligands at sites other than the active site (allosteric sites)
can be either activated or inhibited by allosteric ligands
exist in two major conformational states, R and T
often control key reactions in major pathways, which must be regulated.