Carbamyl Phosphate Binding to Aspartate Transcarbamylase

Carbamyl phosphate, the first ligand in the ordered sequence of binding to the hexameric enzyme aspartate transcarbamylase, binds tightly to half of the active sites in the absence of other ligands.This partial saturation is changed by the binding of succinate, an unreactive aspartate analogue.Succinate binding increases the number of high affinity carbamyl phosphate binding sites from three to six, thereby increasing the number of sites to which it can bind.This unmasking of sites can contribute to the cooperative interactions between active sites in this enzyme.