@entity20538 -tRNA synthetase from @entity375 has been purified to homogeneity. This synthetase was found to be very sensitive to proteases present in the @entity375 extracts and to oxidizing agents of @entity1432 groups. In the absence of protease inhibitors and/or @entity16958 , the enzyme rapidly lost its activity and could not be isolated. The use of these protectors allowed us to obtain different oligomeric structures of the synthetase. In the presence of a minimal concentration of @entity16958 but in the absence of protease inhibitors, a tetrameric @entity20538 -tRNA synthetase of the @entity34215 beta 2 type (alpha = 67 600, beta = 57 500) with a very low specific activity was recovered. With high concentrations of both protectors, a dimeric enzyme was isolated with a specific activity comparable to that for other @entity375 synthetases. The enzyme was of the @entity34215 type where alpha = 70 000--80 000 daltons, depending on whether @entity19668 or @entity8161 was used as the protecting agent. The native form of the enzyme ( @entity34215 ) associated easily with other proteins in various complexes of molecular weights from 250 000 to 300 000, some of them containing @entity56040 -tRNA synthetase. The dimeric @entity20538 -tRNA synthetase was found in equilibrium with its subunits. Diluting the enzyme solution or increasing the salt concentration displaced the equilibrium toward the monomers, which are catalytically inactive for both the tRNA aminoacylation and the @entity7371 - @entity855 exchange reactions. Addition of both tRNAGly and @entity855 . @entity8723 plus @entity2228 displaced the equilibrium toward the dimeric form of the enzyme. @entity1432 groups were found to be involved in the association between the two subunits and in both activities of the synthetase. The results are interpreted in the light of possible regulatory mechanisms of the activity of this synthetase.

@entity20538 -tRNA synthetase from XXXX . Interconversion between active and inactive forms of the enzyme.

@entity16958 :: ('MESH:D004226', 'Chemical') :: ['dithioerythritol'] @entity20538 :: ('CHEBI:46740', 'Chemical') :: ['glycyl', 'Glycyl'] @entity7371 :: ('CHEBI:60614', 'Chemical') :: ['PPi'] @entity2228 :: ('CHEBI:57305', 'Chemical') :: ['glycine'] @entity8723 :: ('MESH:D015636', 'Chemical') :: ['MgCl2'] @entity19668 :: ('MESH:C003614|MESH:D010664', 'Chemical') :: ['phenylmethanesulfonyl fluoride'] @entity855 :: ('MESH:D000255', 'Chemical') :: ['ATP'] @entity1432 :: ('CHEBI:29256', 'Chemical') :: ['Thiol', 'thiol'] @entity34215 :: ('850406(Tax:4932)', 'Gene') :: ['alpha 2', 'alpha 2 = 160 000'] @entity375 :: ('4932', 'Species') :: ['yeast', "baker's yeast"] @entity56040 :: ('CHEBI:37897', 'Chemical') :: ['valyl'] @entity8161 :: ('MESH:D007531', 'Chemical') :: ['diisopropyl fluorophosphate']
@entity375 :: (4932,Species) :: ['baker's yeast']
