22.214.171.124 - Asparagine synthase (glutamine-hydrolyzing)
- Asparagine synthetase (glutamine-hydrolyzing).
- Asparagine synthetase B.
- Glutamine-dependent asparagine synthetase.
ATP + H2O + L-aspartate + L-glutamine = AMP + diphosphate + H(+) + L-asparagine + L-glutamate
There are no Cofactors for this Enzyme
The enzyme catalyses three distinct chemical reactions: glutamine hydrolysis to yield ammonia (which is then channelled to the second active site) takes place in the N-terminal domain. The C-terminal active site mediates both the synthesis of a beta-aspartyl-AMP intermediate and its subsequent reaction with ammonia. However, the exact order of the partial reactions is still somewhat unclear [PMID:9748330, PMID:12706338], here we show the hydrolysis of the glutamate occurring first.
Glutamine hydrolysis occurs at the N terminal. A nucleophilic Cys residue attacks the glutamine substrate, displacing ammonia, forming a substrate-enzyme intermediate which is then hydrolysed. The ammonia diffuses though the interdomain tunnel from the site of production to the site of utilisation: the synthetase component in the C terminal.
A two site ping pong mechanism for the reaction between the aspartic acid, ATP and ammonia has been implicated with several residues thought to be responsible for the binding the substrates through hydrogen bonding interactions.
Kinetic analysis has shown the rate of catalysis at each site to be independent of one another, and so the stoichiometry between the sites must be maintained by the catalytic efficiency of the two sites.
|AA||Uniprot||Uniprot Resid||PDB||PDB Resid|
overall reactant used, proton transfer, unimolecular elimination by the conjugate base, overall product formed, enzyme-substrate complex formation, bimolecular nucleophilic addition, intermediate formation, native state of enzyme regenerated, proton relay, deamination, intermediate collapse, enzyme-substrate complex cleavage
This reaction takes place in the glutaminase domain. The oxyanion initiates an elimination that cleaves ammonia from the bound L-glutamine substrate. Ammonia deprotonates water, which deprotonates the N-terminus of Cys1. The ammonia product is then transferred to the second domain of the enzyme through an internal ion channel
There are no kinetic parameters information for this Enzyme
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