Association-dissociation of mammalian brain glutamine synthetase: effects of metal ions and other ligands

Journal Article · Wed Aug 01 00:00:00 EDT 1984 · Arch. Biochem. Biophys.; (United States)

DOI:https://doi.org/10.1016/0003-9861(84)90559-9· OSTI ID:6586207

Denman, R B; Wedler, F C

Glutamine synthetase from ovine brain has been found to exist in vivo and in vitro as a Mn4E complex, where E is octameric enzyme. Previously observed anomolous effects of added metal ions and protein concentration on the observed specific activity in vitro can now be explained in terms of association-dissociation of the native octamer. In the absence of glycerol, added to stabilize the enzyme for long-term storage, activity decreases sharply below 4 micrograms/ml (20 nM octamer) in assay mixtures due to dissociation of octamer to tetramer and thence to inactive monomer. No dimeric species were detectable under any conditions. The octameric species Mn4EMn4 could be activated further by Mn(II) to form a species Mn4EMn4Mn8 that has a specific activity of ca. 900 U/mg in the transferase assay. Enzyme with one Mn(II)/subunit, Mn4EMn4, associated to octamers more extensively than Mn4E. Analysis of the data by the methods of Kurganov or Thomes and co-workers indicate that the tetramer/octamer equilibrium has a Kd value of ca. 2.5 X 10(-6) M, comparable to values calculated for other enzyme systems. The specific activities for octamer and monomer in the Mg(II)-dependent transferase assay were calculated to be 200 +/- 20 and 0 U/mg, respectively. Tetramers, produced by 2 M urea and then immobilized on CNBr-activated Sepharose 4B, exhibited a specific activity that was 86% of that of the identically treated octamers. Light-scattering experiments showed that, with 1.7-2.0 Mn(II) bound per subunit, the octameric enzyme octamers can associate further to an oligomeric species (Mn4EMn4Mn8)n, where n greater than or equal to 5. This oligomerization also was promoted strongly by lanthanide ions. Mg(II), however, caused only the association of tetramer to octamer.

• Research Organization: Biochemistry Division, Althouse Laboratory, Pennsylvania State University, University Park
• OSTI ID: 6586207
• Journal Information: Arch. Biochem. Biophys.; (United States), Vol. 232:2
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
MAGNESIUM COMPOUNDS
BIOLOGICAL EFFECTS
MANGANESE COMPOUNDS
BRAIN
CATIONS
GLUTAMINE
LIGASES
METABOLISM
ALKALINE EARTH METAL COMPOUNDS
AMIDES
AMINO ACIDS
BODY
CARBOXYLIC ACIDS
CENTRAL NERVOUS SYSTEM
CHARGED PARTICLES
ENZYMES
IONS
NERVOUS SYSTEM
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
TRANSITION ELEMENT COMPOUNDS
560306* - Chemicals Metabolism & Toxicology- Man- (-1987)