.beta.-Galactosidase and production thereof

A powdery .beta.-galactosidase isolated from the culture medium of Penicillium multicolor and having the following characteristics:

• a. having a relative .beta.-galactosidase activity of 224% for o-nitrophenyl-.beta.-D-galactopyranoside and of 186% for p-nitrophenyl-.beta.-D-galactopyranoside when assumed that the relative .beta.-galactosidase activity is 100% for lactose;
• b. having a molecular weight of about 120,000 as determined according to the gel-filtration method;
• c. being active at pH of 2.5 to 7, the optimum pH being at 4.5;
• d. said .beta.-galactosidase activity being lost by heating at pH 6 and at 75.degree. C. for 15 minutes, the optimum temperature being at 55.degree. C.;
• e. said .beta.-galactosidase activity being stable in a pH range of 2.5 to 8.0 when standing at 4.degree. C. for 24 hours;
• f. said .beta.-galactosidase activity being stable at 100% at 60.degree. C. and reduced to 60% at 65.degree. C., to 25% at 70.degree. C. and to 0% at 75.degree. C. when standing at pH 6 for 15 minutes;
• g. said .beta.-galactosidase activity being inhibited by about 20% by the presence of mercuric ion (Hg.sup.++) but being not substantially inhibited by the presence of ferrous ion (Fe.sup.++) and cupric ion (Cu.sup.++) at a metal ion concentration of 10.sup.-3 M;
• and
• h. having an iso-electric point of 5.37 when measured according to an electrophoresis method.