ABSTRACT
An endo-polygalacturonase secreted by Aspergillus sojae was characterized after being purified to homogeneity from submerged cultures with orange peel as the sole carbon source by gel filtration and ion-exchange chromatographies. According to SDS-PAGE and analytical isoelectric focusing analyses, the enzyme presents a molecular weight of 47 kDa and pI value of 4.2. This enzyme exhibits considerable stability under highly acidic to neutral conditions (pH 1.5-6.5) and presents a half-life of 2 h at 50°C. Besides its activity towards pectin and polygalacturonic acid, the enzyme displays pectin-releasing activity, acting best in a pH range of 3.3-5.0. Thin-layer chromatographic analysis revealed that tri-galacturonate is the main enzymatic end product of polygalacturonic acid hydrolysis, indicating that it is an endo-polygalacturonase. The enzyme exhibits Michaelis-Menten kinetics, with KM and VMAX values of 0.134 mg/mL and 9.6 µmol/mg/min, respectively, and remained stable and active in the presence of SO2, ethanol, and various cations assayed except Hg2+.
Subject(s)
Aspergillus/enzymology , Polygalacturonase/chemistry , Polygalacturonase/isolation & purification , Polygalacturonase/metabolism , Carbon/metabolism , Chromatography, Gel/methods , Chromatography, Ion Exchange/methods , Chromatography, Thin Layer/methods , Citrus sinensis/chemistry , Electrophoresis, Polyacrylamide Gel/methods , Enzyme Assays/methods , Enzyme Stability/drug effects , Ethanol/metabolism , Fungal Proteins/chemistry , Fungal Proteins/metabolism , Hexuronic Acids/metabolism , Hydrogen-Ion Concentration , Isoelectric Focusing/methods , Kinetics , Metals/metabolism , Molecular Weight , Pectins/metabolism , Sulfur Dioxide/metabolism , Temperature , Time FactorsABSTRACT
Enzymatic decomposition of gelatin layers on used X-ray films and repeated utilization of the enzyme for potential application in silver recovery were investigated using keratinolytic serine proteases from Purpureocillium lilacinum LPS # 876. At pH 9.0, the enzymatic reaction was enhanced by the increase of enzyme concentration or by the increase of the temperature up to 60â. Under the conditions of 6.9 U/ml, 60â, and pH 9.0, hydrolysis of the gelatin layers and the resulting release of silver particles were achieved within 6 min. The protective effect of polyols against thermal denaturation was investigated. The presence of glycerol and propylene glycol increased enzyme stability. When the reusability of the enzyme for gelatin hydrolysis was tested, it could be seen that it could be effectively reused for more cycles when glycerol was added, compared with the enzyme without protective agents. The results of these repeated treatments suggested that a continuous process of recycling silver from used X-ray is feasible. Keeping in mind that recycling is (at the present time) needed and imperative, it can be remarked that, in this research, three wastes were successfully used: hair waste in order to produce serine proteases; glycerol in order to enhance enzyme thermal stability; and used Xray films in order to recover silver and PET films.
