Abstract
In order to clarify the reason for the variation in specific activities of ribonuclease preparations from Rhizopus sp. ribonuclease (RNase Rh), low specific activity species (RNase Rh') were separated from native RNase Rh by DEAE Toyopearl 650 column chromatography and characterized. When RNase Rh' was subjected to gel electrophoresis in the absence of 2- mercaptoethanol, it gave a 24 kilodalton (kDa) protein band, but in the presence of the reducing agent it gave 17 and 7 kDa bands. These two peptides were separated by gel filtration and their NH2-terminal amino acid sequences were determined. The results indicated that RNase Rh' was an enzyme species cleaved at about the 50th residue of native RNase Rh by proteases during the course of purification, but the two fragments were still covalently joined by S-S bridges. RNase Rh' retained about 70% of the native activity and has a similar conformation to the native enzyme.
