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

Earlier studies showed that two protein components, PI and PII , are concerned with the adenylylation and deadenylylation ofEscherichia coli glutamine synthetase (EC 6.3.1.2). PI by itself catalyzes both adenylylation and deadenylylation, but its activity is modulated by the PII -protein and by glutamine, 2-oxoglutarate, ATP, and UTP, The PII -protein exists in two forms: one form, PII -AT, stimulates PI -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, PII -DA, stimulates adenylylation only if glutamine is present, and also stimulates the deadenylylation activity of PI , which is then dependent upon the presence of ATP and 2-oxoglutarate. Conversion of PII -AT to PII -DA requires the presence of UTP, ATP, and 2-oxoglutarate; it is catalyzed by an enzyme present in PI preparations. UTP may be directly involved in this conversion since PII -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 PII -DA, but not of PII -AT, is destroyed by treatment with snake-venom phosphodiesterase. ATP and 2-oxoglutarate apparently function as allosteric effectors for the conversion of PII -AT to PI -DA.