Variations in the Response of Mouse Isozymes of Adenylosuccinate Synthetase to Inhibitors of Physiological Relevance

• Published in: The Journal of biological chemistry Vol. 278; no. 9; pp. 6673 - 6679
• Main Authors: Borza, Tudor, Iancu, Cristina V, Pike, Evan, Honzatko, Richard B, Fromm, Herbert J
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 28.02.2003
• Subjects: Adenosine Monophosphate - metabolism; Adenylosuccinate Synthase - chemistry; Adenylosuccinate Synthase - genetics; Amino Acid Sequence; Animals; Binding Sites; Blotting, Western; Dimerization; DNA, Complementary - metabolism; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Escherichia coli - metabolism; Fructosediphosphates - metabolism; Guanosine Diphosphate - metabolism; Guanosine Triphosphate - metabolism; Humans; Kinetics; Ligands; Mice; Models, Chemical; Models, Molecular; Molecular Sequence Data; Protein Isoforms; Protein Structure, Tertiary; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Sequence Homology, Amino Acid; Temperature; Ultracentrifugation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M210838200

Vertebrates have acidic and basic isozymes of adenylosuccinate synthetase, which participate in the first committed step of de novo AMP biosynthesis and/or the purine nucleotide cycle. These isozymes differ in their kinetic properties and N-leader sequences, and their regulation may vary with tissue type. Recombinant acidic and basic synthetases from mouse, in the presence of active site ligands, behave in analytical ultracentrifugation as dimers. Active site ligands enhance thermal stability of both isozymes. Truncated forms of both isozymes retain the kinetic parameters and the oligomerization status of the full-length proteins. AMP potently inhibits the acidic isozyme competitively with respect to IMP. In contrast, AMP weakly inhibits the basic isozyme noncompetitively with respect to all substrates. IMP inhibition of the acidic isozyme is competitive, and that of the basic isozyme noncompetitive, with respect to GTP. Fructose 1,6-bisphosphate potently inhibits both isozymes competitively with respect to IMP but becomes noncompetitive at saturating substrate concentrations. The above, coupled with structural information, suggests antagonistic interactions between the active sites of the basic isozyme, whereas active sites of the acidic isozyme seem functionally independent. Fructose 1,6-bisphosphate and IMP together may be dynamic regulators of the basic isozyme in muscle, causing potent inhibition of the synthetase under conditions of high AMP deaminase activity.