Allosteric regulation of catalytic activity: Escherichia coli aspartate transcarbamoylase versus yeast chorismate mutase

Allosteric regulation of key metabolic enzymes is a fascinating field to st udy the structure-function relationship of induced conformational changes o f proteins. In this review we compare the principles of allosteric transiti ons of the complex classical model aspartate transcarbamoylase (ATCase) fro m Escherichia coli, consisting of 12 polypetides, and the less complicated chorismate mutase derived from baker's yeast, which functions as a homodime r. Chorismate mutase presumably represents the minimal oligomerization stat e of a cooperative enzyme which still can be either activated or inhibited by different heterotropic effectors. Detailed knowledge of the number of po ssible quaternary states and a description of molecular triggers for confor mational changes of model enzymes such as ATCase and chorismate mutase shed more and more light on allostery as an important regulatory mechanism of a ny living cell. The comparison of wild-type and engineered mutant enzymes r eveals that current textbook models for regulation do not cover the entire picture needed to describe the function of these enzymes in detail.