PURIFICATION OF THE XENOPUS-LAEVIS DOUBLE-STRANDED-RNA ADENOSINE-DEAMINASE

A double-stranded RNA adenosine deaminase that catalyzes the conversio n of adenosines to inosines in duplex RNA substrates was purified to n ear homogeneity from Xenopus laevis eggs. The final specific activity was approximately 2.0 nmol of inosine min-1 mg-1 at 25-degrees-C and p H 7.9 with a 794-base pair RNA substrate. Sodium dodecyl sulfate-polya crylamide gel electrophoresis revealed a single major approximately 12 0-kDa protein band by silver staining. The purified enzyme migrated wi th an apparent molecular mass of 90 +/- 10 kDa during high performance liquid chromatography. Gel filtration of the partially purified enzym e gave an apparent molecular mass of 210 +/- 20 kDa, suggesting that t he enzyme may dimerize or associate with other cellular components. Su bstrate modification was inhibited by excess substrate, thiol reagents , heparin, and moderate concentrations of monovalent cations.