A kinetic model of cooperativity in aspartate transcarbamylase.

A relatively simple kinetic model is proposed to account simultaneously for data on the binding of carbamyl phosphate and succinate to aspartate trans carbamylase (ATCase), and for the relaxation spectrum associated with this binding. The model also accounts for measurements of the initial velocity of the reaction of ATCase with respect to aspartate and carbamyl phosphate. The principal assumption made is that ATCase consists of three identical noninteracting cooperative dimers. Ordered binding and both sequential and concerted conformational changes in the dimers are needed to account for the properties of ATCase. The values of the parameters of this model can be determined by fitting to existing experimental evidence. Various new quantitative predictions are made that can serve as additional tests of the proposed theory.