ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

calcium metalloenzymes, are completely unable to function. MacGregor et al., (2001)
commented that these amylases are crucial to the carbohydrate metabolism of many
autotrophic and heterotrophic organisms.
a-Amylase catalyzes the break down of 0.-(1,4) glycosidic linkages found in starch
components and other related carbohydrates (DoleekoVli-MareSova et al., 2005). In
autotrophic organisms, sugars are gradually released from starch which has previously
been stored, thus providing energy for proper growth. Amylases have established many
valuable functions within society, some of which are disease testing, fruit ripening and
malt production (Teotia et al., 2001). a-Amylases also play a major part in breaking
down starch in germinating seeds (Jones and Jacobsen, 1991). Usually, the major
constituent ofman's diet is carbohydrate and the main carbohydrate ingested is starch. a­
Amylases are the most important means heterotrophic organisms use to digest starch
(Silva et at., 2000).
Several compounds found in nature are responsible for inhibiting enzymes, especially the
hydrolases (Kokiladevi, 2005). Current investigations in the field of proteinase and
amylase inhibitors and the growing interest in these phytochemicals in industry and
pharmacy have led researchers to inquire directly into their exact biological function.
Some of these inhibitors are proteins which decrease specific enzyme activities, such as
the inhIbitors ofproteases and amylases (Whitaker and Feeney, 1973).
In 1934, Chrzaszcz and Janicki identified AI in wheat and since then, numerous studies
have recognized the fact that a-amylase inhibitors occur naturally in a wide variety of
plants. Richardson (1991) and Franco et al. (2002) proposed that a-Amylase inhibitors
may simply be classified by their tertiary structure into six different classes, which
researchers identify as lectin-like, knottin-like, cereal-type, Kunitz-like, y-purothionin­
like and thautamin-like. The molecular weight, disulfide bond content, three-dimensional
structure and stability to heat and denaturing agent (Teles et at., 2004) differentiate
among these families. Each family of a-amylase inhIbitors shows particular specificity
features:
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