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Modulation of Glutamine Synthetase Adenylylation and Deadenylylation Is Mediated by Metabolic Transformation of the P II -Regulatory Protein

1971; National Academy of Sciences; Volume: 68; Issue: 12 Linguagem: Inglês

10.1073/pnas.68.12.2949

1091-6490

Maria S. Brown, Anthony W. Segal, Earl R. Stadtman,

Amino Acid Enzymes and Metabolism

Earlier studies showed that two protein components, P I and P II , are concerned with the adenylylation and deadenylylation of Escherichia coli glutamine synthetase (EC 6.3.1.2). P I by itself catalyzes both adenylylation and deadenylylation, but its activity is modulated by the P II -protein and by glutamine, 2-oxoglutarate, ATP, and UTP, The P II -protein exists in two forms: one form, P II -AT, stimulates P I -catalyzed adenylylation activity in the absence of glutamine and makes this activity very sensitive to inhibition by 2-oxoglutarate; it does not affect deadenylylation activity. The other form, P II -DA, stimulates adenylylation only if glutamine is present, and also stimulates the deadenylylation activity of P I , which is then dependent upon the presence of ATP and 2-oxoglutarate. Conversion of P II -AT to P II -DA requires the presence of UTP, ATP, and 2-oxoglutarate; it is catalyzed by an enzyme present in P I preparations. UTP may be directly involved in this conversion since P II -DA fractions reisolated by filtration through Sephadex G-100 contain small quantities of a bound uridine derivative that lacks the γ-phosphoryl group of UTP. The activity of P II -DA, but not of P II -AT, is destroyed by treatment with snake-venom phosphodiesterase. ATP and 2-oxoglutarate apparently function as allosteric effectors for the conversion of P II -AT to P I -DA.