title: A simple fractionation protocol for, and a comprehensive study of the molecular properties of, two major endopolygalacturonases from Aspergillus niger.
abstract: A comprehensive study on purification and characterization of the two endopolygalacturonases from Aspergillus niger, PG II and PG IV, accounting for 70% of the total polygalacturonase activity, is reported. These enzymes were purified to homogeneity using ion-exchange chromatography and gel filtration. The enzymes had specific activities of 982 and 3750 units/mg, and their molecular masses were 61 and 38 kDa, respectively. The pH optimum of PG II was pH 3.8-4.3 and for PG IV it was between pH 3 and 4.6, and the temperature optima also differed for the enzymes. The enzymes preferred pectic acid as a substrate, cleaving it at random, leading to the release of oligogalacturonides as products. The K(m) values of the two enzymes were found to be 0.12 and 0.72% respectively. The enzymes were rich in hydrophilic amino acids and relatively low in the sulphur-containing amino acids. Both enzymes were rich in beta-structure and differed in their tertiary folding. The tryptophan residues were in a hydrophobic environment. The enzymes differed in their thermal stability; the midpoint of thermal inactivation, T(m), of the two enzymes was found to be 43 degrees C for PG II and 46 degrees C for PG IV.
authors.affiliation: Department of Protein Chemistry and Technology, Central Food Technological Research Institute, Mysore 570013, India.
authors.forename: Sridevi Annapurna
authors.initials: SA
authors.lastname: Singh
authors.forename: A G
authors.initials: AG
authors.lastname: Appu Rao
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology*; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D011096:Polygalacturonase / Q000302:isolation & purification / Q000378:metabolism*; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: C400187:endopolygalacturonase II; D011096:Polygalacturonase