9603595 Fromm The structure of Adenylosuccinate synthetase from E. coli, the first committed step in the conversion of IMP to AMP in the de novo purine nucleotide biosynthetic pathway, as the unligated enzyme and complexed, with a variety of substrates and substrate analogs, is now available. During the proposed grant period the PI will prepare and study the properties of mutant forms of AMPSase, based on the crystal structure, in an attempt to gain insight into the enzyme's catalytic and regulatory mechanisms at the molecular level. Those mutant forms of AMPSase that appear to be of interest will be crystallized where possible and subjected to structural analysis. The mode of AMPSase regulation is not known; however, the state of subunit association may play a role in the regulation of AMPSase activity and this possibility will be investigated using both kinetic and physical techniques. It was found that mixing of two different inactive mutant forms of AMPSase can lead to the formation of active heterodimers. The physical basis behind this finding will be investigated. *** AMPSase synthetase is an enzyme that plays a crucial role in all living organisms. It catalyzes the first committed step in the biosynthesis of purine nucleic acids, which go on to form DNA and RNA, along with other cellular nucleotides of importance in regulation of metabolism. Understanding how this enzyme functions can also have potential for the design of chemotherapeutic agents. ***
