Studies on the Activity Of α-Amylase Produced from Fusarium spp. using Sweet Potato (Ipomoea batatas) Starch

Studies on the Activity Of α-Amylase Produced from Fusarium spp. using Sweet Potato (Ipomoea batatas) Starch.

ABSTRACT  

After a seven-day pilot studies, day 6 was found suitable for enzyme production from Fusarium species using starch from Ipomoea batatas (sweet potato) tubers as the carbon source. The specific activity of the crude enzyme was 55.45µ/mg. After ammonium sulphate precipitation and gel filtration, the specific activities were found to be 35.93µ/mg and 119.61µ/mg, respectively which corresponds to 3.33-fold purification.

The optimum pH and temperature of the partially purified enzyme were 6.0 and 50o C, respectively. The enzyme activity was strongly activated by Mn2+, Ca2+, and Mg2+ but inhibited by Co2+. The Michaelis constant (Km) and maximum velocity (Vmax) obtained from the Lineweaver-Burk plot of initial velocity data at different substrate concentrations were 5.44mg/ml and 12.57µmol/min, respectively. 

INTRODUCTION  

The α-Amylase (1,4-α-D-glucan glucano hydrolase, EC 3.2.1.1) is the most important carbohydrate degrading enzyme for all starch-based industries viz. food, paper, detergent, pharmaceutical, textile, baking and brewing industries (Gupta et al., 2003). It belongs to the family 13 of glycoside hydrolases (GH13) which randomly cleaves the α-1,4 linkages between adjacent glucose units in starch and related polysaccharides to produce mainly maltodextrins and maltose retaining α-anomeric configuration in the products.

According to the vast majority of known α-amylase structure, it composed of a single polypeptide chain folded into two large domains: N-terminal (A and B) and C-terminal (C) domains. Catalytic domain A contains (β⧸α)8 or TIM barrel structure, domain B consists of three-stranded antiparallel β-sheet structures and protrudes between β3 and α3 of domain A, whereas domain C with a β sheet structure is located in the C-terminal part of the polypeptide chain. Domain B is concerned for the substrate specificity and stability of the enzyme.

Amylases are widespread in animals, fungi, plants and are also found in the unicellular eukaryotes, bacteria, and archaea (Da lagea et al., 2007). Though plants and animals produce amylases, enzymes from microbial sources are generally used in industrial processes. This is due to a number of factors including productivity, thermo stability of the enzyme as well as ease of cultivating microorganisms (Reddy et al., 1999).

Amylases have been reported to be produced by a number of fungi, including Aspergillus, Rhizopus, Fusarium, Candida, Penicillium, Thermomucor, Basidiomycete, Fomitopsis, and Thermomyces (Kunamneni et al., 2005; Balkan and Ertan 2005; Yoon et al., 2006; Kumar et al., 2007; Mohamed et al., 2007). Majority of the studies on fungal amylases are based on mesophiles, rarely on facultative thermophiles (Maheswari et al., 2000). Current researches focus on thermo tolerant enzymes from thermophilic microbial strains. 

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