Modulation of fish liver fructose-1, 6-bis phosphatase by ammonia stress

Abstract

Hepatic fructose 1, 6 bisphosphatase (Fru-P2ase) from Channa punctatus exhibits 100% and 60% elevations of its maximal catalytic rates (Vmax) at pH 7.5 and 9.5 respectively in summer over those in winter. Both the neutral and alkaline activities of the enzyme are enhanced remarkably (100%) in the winter-adapted fish due to exposure to 10 mg N/1 of unionized ammonia for three weeks. While the neutral activity of the purified enzyme is increased in vitro by NH⁺⁴ ions in dose-dependent manner upto about 150 mM NH₄, the alkaline activity is found to be activated at a very low concentration of NH⁴⁺ (25 mM) and inhibited at 100-150 mM NH⁴⁺. The enzyme also shows a characteristics potentiation of 5'-AMP inhibition by NH⁴⁺ (125 mM).