Studies on cellulases of a phytopathogenic fungus, Pyricularia oryzae Cavara. III. Multiplicity of beta-glucosidase, and purification and properties of a second component.
To determine the relationship between the induction patterns of three components of beta-glucosidase of Pyricularia oryzae and carbon sources in the growth medium, various culture conditions were examined. Avicel, hydroxyethylcellulose and methyl-beta-D-glucoside as the carbon source induced both beta-glucosidase components, GB-1 and GB-2, whereas cellobiose and gentiobiose induced only one component, GB-1. Thus, these two components were induced independently and hence thought to be isozymes. The GB-2 was purified to homogeneity by ion exchange and gel filtration chromatographies from two different cultures on methyl-beta-D-glucoside and Avicel. The specific activity of GB-2 when salicin was used as substrate was approximately 5.9 mg glucose/min/mg protein. GB-2 was found to be an oligomeric glycoprotein, which consisted of two subunits with molecular weight of approximately 120,000, comprising a relatively large number of acidic amino acids and mannose, as is the case with GB-1. These two isozymes were clearly different in thermostability, GB-2 being more thermolabile than GB-1. However, the same carboxyl group (pKa 4.2--4.8) was found to be strongly implicated in the formation and dissociation of the enzyme-substrate complex for both of the enzymes, from the analysis of kinetic parameters as a function of pH.
D000596:Amino Acids / Q000032:analysis; D050260:Carbohydrate Metabolism; D002413:Cations, Divalent; D002480:Cellulase / Q000378:metabolism; D004790:Enzyme Induction; D005959:Glucosidases / Q000378:metabolism*; D007700:Kinetics; D003904:Mitosporic Fungi / Q000201:enzymology*; D008970:Molecular Weight; D001617:beta-Glucosidase / Q000302:isolation & purification / Q000378:metabolism*
D000596:Amino Acids; D002413:Cations, Divalent; D005959:Glucosidases; D001617:beta-Glucosidase; D002480:Cellulase