Effect of cultivation conditions on activity of α-amylase from a tropical strain aspergillus flavus link

Abstract

An important integral part of the physiology of the fungal cell is the nature of the cascade of extracellular enzymes produced by fungi. A tropical strain Aspergillus flavus Link obtained from deteriorated tomato (Solanum lycopersicum) fruits grew in a growth nutrient medium composed of MgSO4.7H20, K2HPO4, KH2PO4, FeSO4.7H2O, potassium nitrate and starch at 30°C. Extracellular proteins produced by the isolate in the medium expressed α-amylase activity. The enzyme was partially purified by ammonium sulphate precipitation followed by dialysis. The enzyme exhibited optimum activity at 35°C and at pH 6.0. It possessed an apparent Km of 7.1 mg/ml for the hydrolysis of starch. The enzyme was stimulated by Na+ and Ca2+ but inhibited by ethylenediamine tetraacetic acid and 2,4-dinitrophenol. It lost 64.1% of its activity within 20 min of heating at 80°C. Of the nitrogenous compounds potassium nitrate, ammonium sulphate and casein, casein as nitrogen source in the defined growth medium with starch as carbon source supported most activity of α-amylase by the fungal isolate. Observations during the partial purification and characterization of the enzyme are herein reported.