Purification and Characterization of Iso-Ribonucleases from a Novel Thermophilic Fungus

A thermophilic fungus previously isolated from composted horse manure was found to produce extracellular iso-RNases that were purified 127.6-fold using a combination of size exclusion chromatography and a novel affinity membrane purification system. The extent of purification was determined electrophoretically using 4%–15% gradient polyacrylamide gels. RNase activity was dependent on the presence of a metal co-factor with significantly more activity with Zn(2+) or Mn(2+) than Mg(2+). The RNases exhibited maximum activity at both pH 3.0 and pH 7.0 with no activity at pH 2.0 or 10.0. The optimal temperature for the iso-RNase was 70 °C. The molecular weight of the iso-RNase was determined to be 69 kDa using a Sephadex G-75 column.