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Comparative Study of Amylases from the Midgut Gland of Three Species of Penaeid Shrimp

ABSTRACT Amylases from the midgut gland of wild Farfantepenaeus subtilis (Pérez-Farfante, 1967) and Litopenaeus schmitti (Burkenroad, 1936), and farmed Litopenaeus vannamei (Boone, 1931) were characterized through studies on the effect of inhibitor and metallic ions, optimal pH and temperature, thermal stability and zymograms. The substrate zymogram revealed nine, eight, ten and seven amylolytic bands from F. subtilis, L. schmitti, adults and juveniles L. vannamei, respectively. Total amylolytic activity in the farmed shrimp was three times as high as that of the wild specimens. Amylases from all species exhibited residual activity above 85% at alkaline pH (7.0–8.0), with optimal temperature between 40 and 50°C. None of the enzymes from the species were thermally stable at temperatures above 55°C. Alpha-amylase activity in F. subtilis and L. schmitti was totally inhibited by Type I inhibitor at 50 and 100 µg.mL-1, while enzymes from adult and juvenile L. vannamei retained 43.5 ± 1.98 and 22.5 ± 0.65% of their activity, respectively, at these same concentrations. Ca2+ increased amylase activity in all species only at a concentration of 1 mM, inhibiting activity at 5 and 10 mM. All other ions employed (Cd2+, Zn2+, Hg2+, Cu2+ and Al3+) strongly inhibited amylase activity, regardless of the concentration used.