Inhibitory Study of Ribonuclease L from Aspergillus sp. with Ferric Ion

Inhibitory study of RNase L with ferric ion was performed to clarify the function of the enzyme. The maximal inhibitory pH of ferric ion for the enzyme is in 3.5 ~ 5.0 and the type of inhibition is found to be competitive with the substrate. The Km for RNA and Ki of ferric ion are 1.54 × 10−1 mg/ml and 22.5 µM, respectively.As the recovery of activity from iron-inactivated RNase L is almost completely realized by dialysis against EDTA solution, the inhibition of RNase L with ferric ion is considered to be a reversible reaction. Moreover, the enzyme is rapidly inactivated by methylene blue- or rose bengal-sensitized photooxidation, but the photoinactivation of RNase L is protected in the presence of the competitive inhibitor, ferric ion. It may reasonably be taken as an evidence that ferric ion attacks the active site of the enzyme.