ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

• seed development and mobilization of storage protein during seed gennination or
seedling growth;
• pathogen suppression; and
• pest proteinases."
Proteinase inhibitors which occur naturally play a crucial role in balancing body functions
(Kowalska, 2(07). Protease can be inactivated by being blocked by inhibiturs andIor by
proteins being broken down into simpler substances through hydrolysis (Troncoso et al.,
2007).
Proteinase inhibitors are proteins that bind to proteases, inhibiting proteolytic activity, and
have been detected in animals, plants and microorganisms (Bhattacharyya et aI., 2007;
Rawlings et al., 2004). Zhang et al. (2004) observed the proteinase inhibitors accwnulate
at high levels in many plants becanse of attacks by bacteria and fungi, wounds and plant
hormones. Bhattacharyya et al., (2007) identified 59 individual families of proteinase
inhibitors, which could be classified mainly as serine, cysteine, aspartic or metallo
inhibitors. By the 1930s, the presence of proteolytic enzyme inhibitors had been detected
in plants, although these had been identified in animals during the nineteenth century.
Read and Haas (1938) reported that an aqueous extract of soybean flour inhibited the
ability of trypsin to liquefy gelatin. The fraction of soybean protein responsible for this
effect was partially purified by Bowman (1944) and Birk (1961) and subsequently isolated
in crystalline form by Kunitz (1945).
Proteolytic enzyme inhibitors are widespread throughout all living entities
(Bhattacharyya et aI., 2007). Proteinase inhibitors in plants could be a form of storage
protein (Valueva and Mosolov, 1999) or may be to protect the plant against infections
and disease. Generally, these proteins form part of a defense mechanism in plants to
defend them against proteinases ofpests and pathogens and discourage herbivores (Tiffin
and Gaut, 2001; Tamhane et aI., 2005). Proteinase inhibitors cause amino acid
deficiencies which affect the development and growth of an insect. When gut proteinases
are inhibited or digestive enzymes are vastly over-produced, the insect may die because
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