Ribonuclease production by Aspergillus species

Ribonuclease production by Aspergillus flavipes. A sulphureus and A. fische ri in semisynthetic medium, after 24-144 hours at 30 degrees C under shakin g, was studied. After cultivation, the medium was separated from micelia by filtration and the resultant solution was used as enzymatic extract. The h ighest amount of biomass and RNase was obtained after 96 hours of cultivati on. The enzymes produced by three species presented similar characteristics , with optimum temperature at 55 degrees C and two peaks of activity at pH 4.5 and 7.0. A. flavipes RNases were more sensitive to temperature: 50% of the initial activity was lost after 1 hour at 70 degrees C. After this heat treatment, RNase of A. sulphureus lost 30% of this activity and that of A. fischeri only 16%. The nucleotides released by enzimatic hydrolysis of RNA were separated by ion exchange chromatography in a AG-1X8-formiate column and identified by paper chromatography. This procedure indicated that the r aw enzymatic extract of Aspergillus flavipes is able to hydrolyze RNA, rele asing 3'-nucleotides monophosphate at pH 4.5 and 3' and 5'-nucleotides mono phosphate at pH 7.0 and 8.5. This result suggests that this strain produces two different types of RNase, one acidic and other alcaline, with differen t specificities.