A kinetic method for distinguishing whether an enzyme has one or two active sites for two different substrates. Rat liver L-threonine dehydratase has a single active site for threonine and serine.

We have elaborated a kinetic method which allows us to evaluate whether a Michaelis-Menten-type enzyme acting on two different substrates has one or two active sites. This method has been used with the rat liver L-threonine dehydratase, which catalyzes the dehydrative deamination of both serine and threonine. The experimental data can be fitted to the theoretical plot obtained for the case of a single active site.