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 ºC and demonstrated optimum activity at 30 ºC. 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 ºC for 2 h, but became inactive at 60 ºC after 2 h, and at 70 ºC 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 Sn^{2+} 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 (G_2) and maltotetraose (G_4) were produced in similar magnitude, followed by a distinctly higher amount (> 80%) of maltose. Amylose was the most potential substrate with a K_m value of 1.82 mg/ml. The molecular mass was 50 kDa in the Native PAGE and no multiple forms were observed.

Keywords: Heliodiaptomus viduus, calanoid copepod, zooplankton, amylase

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