Exocellular ribonuclease from Streptomyces aureofaciens II. Properties and specificity

Abstract

1. 1. Properties and specificity of exocellular ribonuclease from Streptomyces aureofaciens BM-K, a strain producing the antibiotic chlortetracycline, were studied. The enzyme had maximal activity at pH 7.0. The optimal temperature has been found to be around 45°. 2. 2. Ribonuclease was inhibited by divalent cations Cu 2+ and Zn 2+ and by increasing ionic strength. 3. 3. The enzyme was relatively heat-stable, the highest stability was observed at pH 7.0. At acidic pH values, the enzyme retained relatively high activity; at basic pH values (about 12) the loss of the activity was nearly 100%. 4. 4. The ribonuclease hydrolyzed yeast RNA to the only mononucleotide, guanosine 3′-phosphate, forming guanosine 2′,3′-cyclic phosphate as intermediate, and to the oligonucleotides with terminal guanosine 3′-phosphate. 5. 5. Polyguanylic and polyinosinic acids, but not polyadenylic, polyuridylic and polycytidylic acids, were split by the low ribonuclease activity. 6. 6. In excess the ribonuclease hydrolyzed polyadenylic acid, as well as polyguanylic and polyinosinic acids, partially hydrolyzed polyuridylic acids. 7. 7. From these results it was concluded that Streptomyces aureofaciens ribonuclease was an endonuclease specific for guanosine 3′-phosphate, similar to the ribonuclease T 1 (ribonucleate 2′-guaninenucleotido-2′-transferase (cyclising, EC 2.7.7.26).