A novel guanyl-preferable ribonuclease of Bacillus polymyxa: isolation and characterization of the enzyme.

Three forms of the extracellular alkaline ribonuclease of B. polymyxa (RNases Bpo I, Bpo II and Bpo III) were obtained in the homogeneous states. Relative molecular weights, N- and C-terminal amino acid sequences of the proteins were determined. The two higher-molecular weight forms of the enzyme (RNases Bpo I and Bpo III) were shown to be precursor molecules which differed from the mature B. polymyxa RNase (RNase Bpo II) by the presence of a extra twelve and six amino acid residues at the amino terminus, respectively. The study of catalytic properties of the enzyme elucidated that the extent of specificity of B. polymyxa RNase in respect to highpolymeric substrates is different from that of other natural Bacillus RNases. Amino acid composition of B. polymyxa RNase was established and structural similarity within family of Bacillus RNases is discussed. B. polymyxa RNase was shown to be inhibited by intracellular protein inhibitor of B. amyloliquefaciens RNase with the dissociation constant of 2.7 x 10(-12) M.