Influence of the temperature and pH on the level of the activity of the digestive enzymes of Siberian sturgeon

The adaptations of the enzymes of intestinal mucous tunic of Siberian sturgeon to the environ-mental factors (temperature and pH) are studied. It is shown that the temperature optimum for the alkaline phosphatase is located in the range 60–65 °С, for the amylase – 30 °С, for the maltase – 55 °С, for caseinlytic proteinases – 40 °С. It is stated that the studied enzymes of Siberian sturgeon save sufficiently high relative activity at low (0 °С) incubation temperature. Maximum activity of alpha-amylase, maltase, alcaline phosphatase is registered at pH 8–9, 7, 8–9, and 9–10 accordingly, for caseinlytic proteinases optimal value of pH is located in the range 8–10. These pH optimums are in concordance with similar optimums of fishes of the Volga river basin. Siberian sturgeon inhabits in conditions of lower temperature in comparison with species of the Volga river basin, probably it caused the shift of temperature optimums of alpha-amylase and caseinlytic proteinases in the direction of lower temperature values. Besides it should be noted that response of digestive enzymes of Siberian sturgeon on the change of incubation temperature is similar to analogous phenomenon of arctic fishes. It is confirmed that temperature adaptations of the digestive system of poikilotherm animals are carried out mainly due to changes of enzyme systems.