Avian mitochondrial glutamine metabolism.

Area of Science:

• Biochemistry
• Cell Biology
• Animal Physiology

Background:

• Avian liver mitochondria possess glutamine synthetase.
• Ammonia detoxification is crucial for purine biosynthesis.

Purpose of the Study:

• To investigate glutamine synthesis from glutamate in avian liver mitochondria.
• To determine the role of mitochondrial glutamine synthetase in ammonia detoxification.

Main Methods:

• Using L-[U-14C]glutamate and L-[15N]glutamate as substrates.
• Measuring 14CO2 release for glutamate deamination.
• Employing mass spectrometry to analyze glutamine.
• Studying L-glutamine permeability using rapid centrifugation.

Main Results:

• Mitochondria synthesized glutamine from glutamate without exogenous ATP or ammonia.
• A 1:1 stoichiometry was observed between glutamate deamination and amidation.
• 15N was incorporated into both alpha-amino and amide groups of glutamine.
• L-glutamine transport across the mitochondrial membrane is rapid and passive.
• Mitochondrial glutamine synthetase converts intramitochondrial ammonia to glutamine.

Conclusions:

• Mitochondrial glutamine synthetase is the primary site of ammonia detoxification in avian liver.
• Synthesized glutamine is effluxed to the cytosol for purine (uric acid) biosynthesis.