Studies on extracellular ribonucleases of Ustilago sphaerogena. Purification and properties

Abstract

1. Four ribonucleases were isolated from culture media of Ustilago sphaerogena. They were designated ribonucleases U1, U2, U3 and U4. 2. They were purified about 1600-, 3700-, 1100- and 16-fold respectively. 3. It was shown by gel filtration that ribonucleases U1, U2 and U3 have molecular weights about 10000 like ribonuclease T1, and that ribonuclease U4 is much larger. 4. Ribonucleases U1, U2 and U3 are thermostable, but ribonuclease U4 is not. 5. The pH optimum of ribonucleases U1 and U4 is pH8·0–8·5, and that of ribonucleases U2 and U3 is pH4·5.