ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...
ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ... ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...
B1.4.3.2 inhibitor molecule generally occupy the subsites of the enzyme (iii) structmal elements involved in the inlnbition action are likely to correspond to flexible components of the free structures ofthe molecules. Literature (Sharma and Pattabiraman, 1980, 1982; Ida et al., 1994) indicates that many AI present in tubers are active against mammalian amylases, but exlnbit no activity on plant amylases. It is apparent that the two AI present in Amadumbe will complement each other, providing the Amadumbe tubers with a wider spectrum against intruders. It is apparent that both inhIbitors had no effect on fungal amylase. Amadumbe grow in moist, humid conditions and fungal infections are prevalent. It is possible that fungus has become resistant to the action of a-amylase inhibitors. Sharma and Pattabiraman (1982) have reported simiIar results for Dioscorea alala. Bifunctional properties have been demonstrated by a number of inhIbitors and have therefore received particular attention as appealing candidates for pest-contro!. This biological activitiy of inhibitors, inhIbiting both serine proteinases and a-amylases, is very useful (Maskos et al., 1996). a-Amylase inhibitors show great variety in their effectiveness against target enzymes. a-Amylase inhibitors found in wheat (Franco et aI., 2000), barley (Richardsoll, 1991) and Indian finger millet (Campos and Richardson, 1983) efficiently inhibit a-amylases from different insect sources. Thus, these a-amylase inhibitors can play a key role in plant defense against pests and pathogens. Effect oftemperature on inhibitor activity Temperature is one of the most important parameters that affect the rate of enzyme hydrolysis. The optimum temperature displayed for both inhIbitors was 40° C and, at extreme temperature, inhibitors became inactive. Optimum temperature for the navy-bean amylase inhibitor was 37° C, but activity was lost at 90° C (Hoover and Sosulski, 1984). A similar optimum temperature of 37° C was also observed for the a-amylase inhibitor from a Pacchyrhizus erosus tuber (Noman et al., 2006). It can be concluded from these 138
Bl.4.3.3 results that amylase inhibitors are fairly heat-stable (PratInbha et al., 1995) and that the residual activity inprocessed Amadumbe (Section A) could be attrIbuted to this property. Effect ofpH on the interaction ofamylase with the inhibitor The AI protein was not active at acidic pH. The proteins isolated from Colocasia antiquorum (Sharma et aI., 2006) were basic proteins. Because of the two peaks of optimal pH points, it is possible that isoenzymes are present. A similar optimum pH 7.0 was observed for the a-amylase inhibitor from the P. erosus tuber (Noman et al., 2006). The partially purified and characterized a-amylase inhibitors from Amadumbe showed similar properties when compared with a-amylase inhibitors from other tubers. Although the Amadumbe a-amylase inhibitors showed activity against mammalian amylases, processing greatly inactivated the biological activity ofthe inhibitors. 139
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Bl.4.3.3<br />
results that amylase inhibitors are fairly heat-stable (PratInbha et al., 1995) and that the<br />
residual activity inprocessed Amadumbe (Section A) could be attrIbuted to this property.<br />
Effect ofpH on the interaction ofamylase with the inhibitor<br />
The AI protein was not active at acidic pH. The proteins isolated from Colocasia<br />
antiquorum (Sharma et aI., 2006) were basic proteins. Because of the two peaks of<br />
optimal pH points, it is possible that isoenzymes are present. A similar optimum pH 7.0<br />
was observed for the a-amylase inhibitor from the P. erosus tuber (Noman et al., 2006).<br />
The partially purified and characterized a-amylase inhibitors from Amadumbe showed<br />
similar properties when compared with a-amylase inhibitors from other tubers. Although<br />
the Amadumbe a-amylase inhibitors showed activity against mammalian amylases,<br />
processing greatly inactivated the biological activity ofthe inhibitors.<br />
139
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