Tissue glutamine synthetase associated with ammonia detoxication and nitrogen metabolism in Clarias batrachus

Abstract

The composition of reaction mixture of glutamine synthetase (GS) assay system was perfected and utilized to determine the activity of this enzyme spectrophotometrically in selected tissues of the freshwater teleostean fish, Clarias batrachus. Of these tissues, brain was found to contain comparatively a very high activity representing a rapid role of GS in ammonia detoxication and synthesis of essential neurotransmitter substance in this tissue. Of other tissues, liver, kidney and gill were found to contain significant activities in the order representing their relative metabolic activities. The study was extended by examining the brain (neural) and liver (non-neural) GS system in more detail with a view to see the alterations (if any). GS activity of both, neural and non-neural tissues was found to be the same and also in the range reported for other Vertebrates. Observations regarding kinetic, physical and chemical properties of the enzyme are reported. Maximum enzyme activity was observed at pH 7.2 to 7.4 and temperature 35°C. The enzyme was found to be more stable at 25 °C while activity decresased at higher temperatures (above 40°C) and showed no activity at 60°C (liver) and 70°C (brain). A comparison and possible physiological roles of the enzyme for the concept of ammonia excretion, protein synthesis and nitrogen metabolism in teleostean fish tissues are discussed.