Purification and properties of alanyl-tRNA synthetase from Bombyx mori: a monomeric enzyme.

Alanyl-tRNA synthetase was purified from the posterior silk glands of Bombyx mori by ammonium sulfate fractionation and chromatography on DEAE-Sephacel and hydroxyapatite columns. The yield was about 100 mg of the enzyme per 1 kg of the glands. The enzyme required both L-alanine and alanine tRNA for pyrophosphate formation from ATP. The PPi formation was observed even after tRNA was fully aminoacylated. The enzyme was found to be a monomer of 115K daltons by SDS-polyacrylamide gel electrophoresis, gel filtration and suberimidate cross-linking experiments. The monomeric enzyme did not dimerize in the presence of the alanine tRNA. The enzyme and the tRNA formed a 1:1 complex. The results indicate that Bombyx mori alanyl-tRNA synthetase functions in a monomeric state.