Purification and Characterization of a Ribonuclease from <i>Aspergillus giganteus IFO 5818</i>, the Gigantin

Abstract

A protein has been isolated from a culture medium of Aspergillus giganteus IFO 5818 (gigantin) and purified by ion-exchange chromatography successively on DEAE-cellulose and carboxymethyl-cellulose, and gel-filtration chromatography on Biogel P10. With a high purity, gigantin was found to be a non-glycosylated basic protein with a relative molecular mass of 17000 +/- 200 determined in PAGE/SDS. Gigantin was able to digest the synthetic homopolymers of nucleic acids poly(A), poly(I), poly(C) and poly(U). The catalytic action has an optimal pH around 7.0, an optimal temperature at 45-55 degrees C and can be inhibited by cations. Gigantin activity, analyzed as its capacity to hydrolyze RNA from yeast, was comparable to that of alphasarcin, a similar biochemical protein produced by the strain A. giganteus MDH 18894. A study of the substrate specificity for alphasarcin indicated a preference for poly(A) and poly(I), while gigantin had greater activity on poly(C) and poly(U). The cross reaction of gigantin with a rabbit antiserum to alphasarcin suggests a high sequence similarity between both proteins. However, gigantin is immunologically distinguishable from alphasarcin as alphasarcin antiserum detects epitopes in alphasarcin that are not present in gigantin.