Glycyl- and alanyl-tRNA synthetases from Bombyx mori. Purification and properties.

Glycyl- and alanyl-tRNA synthetases have been purified from an extract of Bombyx mori posterior silk glands by a procedure that allows for the simultaneous isolation of both enzymes. Glycyl-tRNA synthetase is a dimer of Mr = 160,000 consisting of similar or identical subunits, whereas alanyl-tRNA synthetase is a monomer of Mr = 110,000 to 115,000. The abundance of these two enzymes in the posterior silk gland is consistent with the observed adaptation of this organ to the production of the silk protein, fibroin. The two enzymes are similar in oligomeric structure to the corresponding enzymes in Saccharomyces cerevisiae, but dissimilar from their counterparts in Escherichia coli.