The synthase(合酶)and synthetase（合成酶): Synthase is (enzyme) that catalyzes the synthesis of a biological compoundbut, unlike synthetases, does not make use of ATP as a source of energy.: Synthetase is (enzyme) any ligase that synthesizes biological compoundsusing ATP as a source of energy.: The amino acids glutamate and glutamine play essential roles in this regard,acting as nitrogen donors for most amino acids
The synthase(合酶) and synthetase (合成酶) • Synthase is (enzyme) that catalyzes the synthesis of a biological compound but, unlike synthetases, does not make use of ATP as a source of energy. • Synthetase is (enzyme) any ligase that synthesizes biological compounds using ATP as a source of energy. • The amino acids glutamate and glutamine play essential roles in this regard, acting as nitrogen donors for most amino acids
Glutamine Synthetase: GS in E. coli is regulated in three ways:·Feedbackinhibition·Covalentmodification: Gene expression and protein synthesis control the amount of GS in cellsBut no such regulation occurs in eukaryotic versions of GS
Glutamine Synthetase • GS in E. coli is regulated in three ways: • Feedback inhibition • Covalent modification • Gene expression and protein synthesis control the amount of GS in cells But no such regulation occurs in eukaryotic versions of GS
Allosteric Regulation of Glutamine SynthetaseGhutamateNH+OGheneATIADP5OHCHNinedifferentfeedbackGhutamininhibitors.NHAME1NH
Allosteric Regulation of Glutamine Synthetase Nine different feedback inhibitors
Covalent Modification of Glutamine Synthetasemyhylated Tyr: Each GS subunit can be adenylylated at a specific tyrosine residue (Tyr397)inanATP-dependentreaction·AdenylylationinactivatesGS: Adenylyl transferase catalyzes both the adenylylation and deadenylylation
Covalent Modification of Glutamine Synthetase • Each GS subunit can be adenylylated at a specific tyrosine residue (Tyr397) in an ATP-dependent reaction. • Adenylylation inactivates GS. • Adenylyl transferase catalyzes both the adenylylation and deadenylylation
Glutamine synthetase is regulated through gene expression: The gene that encodes the GS subunit in E. coli is designated GlnA: The GlnA gene is actively transcribed to yield GS mRNA fortranslation and synthesis of GS protein only if a specifictranscriptional enhancer, NRI, is in its phosphorylated form
Glutamine synthetase is regulated through gene expression • The gene that encodes the GS subunit in E. coli is designated GlnA. • The GlnA gene is actively transcribed to yield GS mRNA for translation and synthesis of GS protein only if a specific transcriptional enhancer, NRI, is in its phosphorylated form