Characterization of glutamine synthetase from avian liver mitochondria

1. Glutamine synthetase has been purified to homogeneity from chicken liver mitochondria. 2. The native enzyme is an octamer composed of identical subunits with monomeric mol. wt of 42,000 dalton. 3. Apparent Kms for NH4+, ATP and glutamate were 0.5, 0.9 and 6 mM, respectively. D-Glutamate and L-alpha-hydroxyglutarate were utilized as substrates with activities approx. 40% those obtained with glutamate. Of several nucleotides tested, none were effective replacements for ATP. 4. Heavy metal ions were inhibitory as were Mn2+, Ca2+ and lanthanide ions. 5. Despite its different subcellular localization and physiological function, avian glutamine synthetase is markedly similar to the weakly-bound microsomal rat liver enzyme with respect to a number of physical and chemical properties.