Augmentation by β-aspartyl phosphate of threonine control of the dehydrogenase activity of the aspartokinase-homoserine dehydrogenase complex

Abstract

In the presence of low levels of magnesium adenosine triphosphate and moderate levels of potassium ion, the amount of threonine required for control of the dehydrogenase activity of the aspartokinase-homoserine dehydrogenase complex of Escherichia coli can be reduced about six-fold by the presence of very low amounts of β- L = -aspartyl phosphate. β-Aspartyl phosphate appears to enhance the binding of threonine to the complex with retention of a competitive-like but sigmoidal response of homoserine in overcoming the inhibitory effect of threonine. Enhancement of control of the dehydrogenation activity by the product of the kinase activity of the enzyme complex offers another basis for an advantage of the dual enzyme system over separate enzymes.