[Tryptophanyl-tRNA-synthetase: limited proteolysis by elastase and isolation of "one-site" enzyme]

Each subunit of the dimeric tryptophanyl-tRNA-synthetase from beef pancreas is subjected to limited hydrolysis by elastase in two stages, according to scheme: 60 00 +/- 2000 leads to 51 000 +/- 2000 leads to 40 000 +/- 1500 daltons. In the course of the second step tryptophanyl-tRNA-synthetase looses its enzymatic activity. In the presence of substrates the pattern of fragments does not change. Formation of tryptophanyladenylate enzyme complex decreases the rate of proteolysis. Using the ability of synthetase to form one mole of stable aminoacyladenylate per mole of synthetase, the "one-site" enzyme was obtained by action of elastase on aminoacyladenylate-enzyme complex. This "one-site" enzyme consists of two subunits, one of which has a molecular weight of 51 000 daltons and is active and the other has a molecular weight of 40 000 daltons and is inactive. The "one-site" enzyme had Km values for all substrates for both aminoacylation and ATP--[32P]PP exchange reactions which are similar to values of Km for the native enzyme.