The effect of temperature, pH and salt on amylase in Heliodiaptomus viduus (Gurney) (Crustacea: Copepoda: Calanoida)

Abstract

An interesting a-amylase has been obtained in large quantity (2400 U/g of body weight) with specific activity (20.22 U/g protein) from a freshwater zooplankton, Heliodiaptomus viduus (Gurney). Partially purified enzyme showed activity up to 70 ¼C and demonstrated optimum activity at 30 ¼C. The enzyme was active between pH 3.5 and 8.5, with maximum activity at pH 6.0. It retained its full activity at 30 ¼C for 2 h, but became inactive at 60 ¼C after 2 h, and at 70 ¼C after 1 h. Enzyme activity was retained at 60% in 2 M NaCl after 24 h incubation, while full activity was found in 0.5 M NaCl for the same duration of incubation. Addition of metal ions like $Fe^{2+}, Ba^{2+}, Co^{2+}, Ag^{2+}$ , and $Mn^{2+}$ enhanced activity up to 130%-200% of the original activity, while K+ and Sn2+ caused a negligible increase in the activity. Addition of $Hg^{2+} and Li^{2+}$ completely inhibited amylase activity, whereas $Cu^{2+}, Mg^{2+}$ , and $Pb^{2+}$ reduced activity to as little as 5% of original activity. Soluble starch, amylose, and amylopectin were completely digested by this amylase, whereas glycogen was hydrolyzed to a lesser extent. During hydrolysis of soluble starch, initially, maltose (G2) and maltotetraose (G4) were produced in similar magnitude, followed by a distinctly higher amount (> 80%) of maltose. Amylose was the most potential substrate with a Km value of 1.82 mg/ml. The molecular mass was 50 kDa in the Native PAGE and no multiple forms were observed.