CHEMICAL COUPLING OF GLUCOAMYLASE PRODUCED BY Arthrobotrys conoides ONTO COTTON CLOTH AND Ocimum basilicum SEEDS AND CHARACTERIZATION OF THE IMMOBILIZED ENZYME

摘要

Glucoamylase produced by Arthrobotrys conoides was immobilized onto cotton cloth pieces (CC) and seeds of Ocimum basilicum (OB) employing five different approaches. Mechanical stability of CC and large surface area provided by the microfibrillar structure in the mucilage of OB seeds offers the advantage for their use as immobilization matrices. Periodate treated enzyme coupled to polyethylenimine treated support gave the best results with immobilization percentage of 67.5 and 53 for CC and OB seeds respectively. Immobilized enzymes exhibited broader pH and temperature activity profiles as compared to those of native and PI oxidized forms. Immobilization conferred stability to the enzyme in acidic region and also improved its thermo-stability. Km values for starch were found to be 0.08 and 0.105 mg.ml-1 for native and PI treated forms and, 2.3 and 2.6 mg.ml-1 for enzymes bound to CC and OB respectively. Although the enzyme preparations were optimally active at 50?C, recycling studies indicated optimum temperature of 40?C for saccharification of starch. CC and OB bound preparations could be recycled 13 and 11 times respectively every 2h at 40?C, with retention of 50% activity. Immobilized preparations were able to convert starch to an extent of 61-64%. Conversion percentage improved to 73% when CC preparation was incubated with starch at increased speed of agitation indicating diffusional limitations as one of the factors influencing the apparent decrease in the affinity of the immobilized enzyme for its substrate. Cloth bound preparation was found to be superior in its performance in comparison to enzyme coupled to OB.