Alkaline‐pH‐actingdigestive enzymes of the polyphagous insect pest Spilosoma obliqua: stabilityand potential as detergent additives

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Abstract
The gut contents of the fifth‐instar larvae of the polyphagous insect pest Spilosoma obliqua reared on castor‐bean leaves exhibit high proteolytic, amylolytic and lipolytic activities. While the pH optimum of proteolytic activity was 11.0, those of amylase and lipase were 9.0 and 8.0 respectively. Among these, the lipase had a temperature optimum of 40 ° C; the amylolytic and proteolytic activities peaked at 50 ° C. All three enzyme activities could be nearly quantitatively precipitated from the gut contents at 60′ (NH4)2SO4 saturation. The protease, amylase and lipase in the fraction obtained thus were reasonably stable at 40 ° C and retained over 20, 41 and 50% activities respectively after 24 h at pH 9.0. Glutaraldehyde treatment of the dialysed ammonium sulphate fraction resulted in a marked improvement in the retention of enzyme activities at 40 ° C. The ammonium sulphate fraction was also highly effective in facilitating the removal of old bloodstains from cotton cloth in both the presence and absence of detergents.

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