PURIFICATION AND SOME PROPERTIES OF TWO ACID RIBONUCLEASES FROM THE MYCELIA OF ASPERGILL US NIGER

Abstract

Acid ribonuclease (RNase) was extracted from mycelia of Aspergillus niger 1617 and separated into two fractions designated acid RNases I (EC 3.1.27.1) and II (EC 3.1.27.3). Each fraction was partially purified and its enzymatic properties were examined. The molecular weight of acid RNase I was approximately 45, 000, and that of II was 13, 000. The optimal pH of acid RNase I was 3.5 and that of II, 4.5. Acid RNase I was inhibited markedly by Fe³⁺, Cu²⁺, Hg²⁺ and 5′-ATP, whereas II was inhibited markedly by Fe³⁺. Acid RNase I had no base specificity producing 3′-monophosphates of the four nucleosides and guanosine-2′, 3′-cyclic monophosphate. Acid RNase II was a guanine-specific RNase.
Changes in the activity of acid RNases I and II were studied during culture on agar medium. The activity of acid RNases I and II increased and reached their maxima during the late phase of active growth. After their maxima, the activity of acid RNase I remained unchanged, while that of II decreased and finally disappeared.