Annual variations in the specific activity of fructose 1,6-bisphosphatase, alanine aminotransferase and pyruvate kinase in the Sparus aurata liver

We determined the annual change in the intermediary metabolism of glucose through the variations of specific activity of fructose 1,6-bisphosphatase (FBPase), alanine aminotransferase (AAT) and pyruvate kinase (PK). Fish (average mass 330 g) were kept in cages under natural conditions of temperature and photoperiod and fed with a commercial diet. FBPase, AAT and PK increased their activity in June in different ways: AAT and PK increased Vmax, and FBPase increased the velocity at subsaturating substrate concentrations, changing Km. The reproduction period modified the annual tendency of changes in the enzyme activities in both parameters, Km and Vmax, except for Km of PK which shows a circa-annual rhythm. No relation between the changes of enzymes activity and photoperiod or temperature has been found in this study, except for Km of AAT which presents a positive correlation with photoperiod and a negative correlation with temperature.