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 30oC. 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 35oC 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 80oC. 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.