The Effect of Temperature, pH, and Salt on Amylase in Heliodiaptomus viduus (Gurney) (Crustacea: Copepoda: Calanoida)

An interesting α-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 Fe2+, Ba2+, Co2+, Ag2+, and Mn2+ enhanced activity up to 130%-200% of the original activity, while K+ and Sn2+ caused a negligible increase in the activity. Addition of Hg2+ and Li2+ completely inhibited amylase activity, whereas Cu2+, Mg2+, and Pb2+ 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.