Abstract
Pure Michaelis-Menten enzymes have been studied (i.e., enzymes with a hyperbolic (S, V) behavior in a well-stirred solution). When such enzymes are associated with a structure in vitro, even in the simplest conceivable form (immobilization in a homogeneous gel), they can produce enzymic or transport reactions with many different kinetics (Michaelis-Menten, sigmoidal, dual-phasic, etc.). Therefore, when structured enzyme or transport processes in vivo have sigmoidal kinetics, it is not proof that the corresponding proteins are allosteric. In same manner, when the apparent kinetics are dual-phasic, it is not proof that two enzyme, or transport systems, coexist.