Biochemical characterization and modulation by abscisic acid of aminopeptidase‐N activity in the digestive tract of Dentudo <scp><i>Oligosarcus jenynsii</i></scp> from Mar Chiquita coastal lagoon (Buenos Aires, Argentina)

The determination of the existence and level of activity of specific digestive enzymes is commonly used as a tool to understand the functioning of the digestive machinery. The aim of this study was to determine the existence and biochemical characteristics of aminopeptidase-N (APN) activity in the digestive tract of Oligosarcus jenynsii from Mar Chiquita coastal lagoon (Buenos Aires) and its possible modulation by abscisic acid (ABA). Individuals were collected in November 2022 from freshwater tributaries of the coastal lagoon using a beach seine net. Juveniles and adults were immediately placed on ice after capture, whereas additional groups of juveniles were transported to the laboratory for in vitro experiments. Juveniles and adults exhibited APN activity in the intestine and liver, which was active across a wide range of pH and temperature, and followed Michaelis-Menten kinetics. Bestatin inhibited the activity in the intestine in both stages, but it had no effect on the liver. Adults exhibited higher specific APN activity in the intestine compared to juveniles. The presence of ABA in vitro decreased APN activity in both intestine and liver from juveniles. These results suggest the presence of APN in both juveniles and adults, as well as its differential modulation by ABA in juveniles.