Inosine monophosphate (IMP) is a precursor of the two purine nucleotides, adenosine monophosphate (AMP) and guanosine monophosphate (GMP)e through DEAE-Scphacex, and the reaction IMP~ XMP is catalyzed by: IMP dehydrogenase which was purified in a manner similar to adenylosuccinate synthetase. Adenylosuccinate synthetase of rat liver is stimulated maximally with 10-9 M L-T 3 or 10-5 M L-T4 , but not by D in vivo effects. Further correlation to in vivo studies was obtained from brain and testes tissues. / Ph. D.