Functional Differences of Digestive Proteases in Three Fish Species of the Genus Poblana (Atheriniformes: Atherinopsidae)

The populations of three members of the Neotropical silverside fish from the Poblana genus of the Atherinopsidae family ( Poblana alchichica , P. letholepis , and P. squamata ) are microendemic species restricted to the eastern basin of central Mexico, where each Poblana species is limited to each crater lake. The aim of this study was to characterize the potential differences in functionality and diversity of digestive proteases between three Poblana species as a likely result of physiological digestive adaptations over the speciation process. Adults of the three Poblana species were collected from three different crater lakes and the activity of digestive proteases and their functional characteristics under different pH and temperature conditions and the number and size of alkaline proteases were determined using biochemical and electrophoretic techniques. The three Poblana species showed acid protease activity and high chymotrypsin activity; likewise, the optimum pH was 8 for alkaline proteases and ranged between 2 and 3 for acid proteases. Alkaline proteases showed an optimum temperature peak at 60°C, while acid proteases showed two peaks (at 30°C and 60°C). The presence of aspartyl peptidases in all three species was confirmed using an inhibitor pepstatin A. The SDS-PAGE zymogram showed four activity bands with alkaline proteolytic activity (45.4, 39.0, 27.9, and 17.4 kDa) in P. alchichica , five bands (58.0, 45.4, 39.0, 27.9, and 17.4 kDa) in P. letholepis , and five bands (126.9, 69.7, 39.0, 27.9, and 17.4 kDa) in P. squamata . Therefore, the studied Poblana display slight differences in protease function and in the number of protease isoforms as a result of allopatric speciation processes and probably of diet selectivity.