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J. Biochem, 1980, Vol. 87, No. 4 1203-1208
© 1980 Japanese Biochemical Society

research-article

Studies on Cellulases of a Phytopathogenic Fungus, Pyricularia oryzae Cavara

IV. Kinetic Studies on ß-Glucosidases

Toshiya HIRAYAMA, Hideo NAGAYAMA* and Kazuo MATSUDA

Department of Agricultural Chemistry, Faculty of Agriculture, Tohoku University Sendai, Miyagi 980
*The Research Institute for Tuberculosis and Cancer, Tohoku University Sendai, Miyagi 980

Kinetic studies of the two ß-glucosidase isozymes, GB-1 and GB-2, which were purified from the culture filtrate of a phytopathogenic fungus Pyricularia oryzae, revealed that the latter isozyme was an allosteric protein with two substrate binding sites. The homotropic effects of o- and m-nitrophenyl-ß-D-glucosides on GB-2 showed positive cooperativity, whereas that of cellooligosaccharide showed negative cooperativity.

The affinity of GB-2 for cellooligosaccharide tended to increase with decreasing chain length, in contrast to that of GB-1. Glucono-{delta}-lactone and glucose acted as competitive inhibitors of GB-1 and GB-2.

As regards the control of the level of glucose formed by the cellulase system, it appears that the rate of formation of glucose by ß-glucosidase is reduced by the presence of the substrate, cellooligosaccharide, as well as by the product, glucose.


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