Kinetic characterization of NADP-specific glutamate dehydrogenase from the sea anemone, anthopleura xanthogrammica: Control of amino acid biosynthesis during osmotic stress
1. 1. Glutamate dehydrogenase (GDH) from the sea anemone, Anthopleura xanthogrammica, was purified 430-fold to a final specific activity of 61.1 units/mg protein. 2. 2. The enzyme was a hexamer of molecular weight 325,000±5000 and subunit size 49,000. 3. 3. The enzyme was NADP(H) specific and utilized L-glutamine as an alternative substrate for ammonium ion; activity ratios, NH4 + vs glutamine, were 11:1 at pH 7 and 2:1 at pH 8. 4. 4. Kinetic constants, S0.5, for the reverse reaction were 61±4, 0.59±0.06 and 0.0091±0.0011 mM for NH4 -, α-ketoglutarate and NADPH for the NH4 + linked reaction and 5.1±1.0, 1.2±0.2 and 0.0027±0.004 mM for glutamine, α-ketoglutarate and NADPH for the glutamine linked reaction. 5. 5. The enzyme was not affected by allosteric modifiers, ADP, ATP, GTP or leucine but was affected by inorganic ions; salts (KCl, NaCl, K2SO4 or potassium phosphate) activated the reverse direction and had an inhibitory effect on the forward direction. 6. 6. Effects of salts on GDH would promote the de novo synthesis of glutamate during hyperosmotic stress giving GDH an important role in the synthesis of amino acids as intracellular osmolytes during adaptation to changes in external salinity.
|Journal||Comparative Biochemistry and Physiology -- Part B: Biochemistry and|
Male, K.B. (Keith B.), & Storey, K. (1983). Kinetic characterization of NADP-specific glutamate dehydrogenase from the sea anemone, anthopleura xanthogrammica: Control of amino acid biosynthesis during osmotic stress. Comparative Biochemistry and Physiology -- Part B: Biochemistry and, 76(4), 823–829. doi:10.1016/0305-0491(83)90399-1