1993, English, Article edition: Trp59 to Tyr substitution enhances the catalytic activity of RNase T1 and of the Tyr to Trp variants in positions 24, 42 and 45 Grunert, Hans-Peter; Landt, Olfert; Zirpel-Giesebrecht, Maria; ...

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Published
  • Oxford University Press
  • 1993-09-01 00:00:00.0
Language
  • English

Edition details

Title
  • Trp59 to Tyr substitution enhances the catalytic activity of RNase T1 and of the Tyr to Trp variants in positions 24, 42 and 45
Author
  • Grunert, Hans-Peter
  • Landt, Olfert
  • Zirpel-Giesebrecht, Maria
  • Backmann, Jan
  • Heinemann, Udo
  • Saenger, Wolfram
  • Hahn, Ulrich
Published
  • Oxford University Press
  • 1993-09-01 00:00:00.0
Physical Description
  • text/​html
Subjects
Notes
  • Using point mutated overproducing strains of E.coli , ribonuclease T1 was prepared with the single substitutions Tyr24Trp, Tyr42Trp, Tyr45Trp or Trp59Tyr and the corresponding double substitutions Tyr24Trp&​sol;Trp59Tyr, Tyr42Trp&​sol;Trp59Tyr and Tyr45Trp&​sol;Trp59Tyr. Steady state kinetics of the transesterification reaction for the two dinucleoside monophosphate substrates guanylyl-3′, 5′-cytidine and guanylyl-3′, 5′-adenosine indicate that the tryptophan can be introduced in different positions within the ribonuclease T1 molecule without abolishing enzymatic activity. The Trp59Tyr exchange even enhances catalysis of the cleavage reaction ( k cat &​sol; K m ) relative to the wild type enzyme and similar effects are found with single tyrosine to tryptophan substitutions. For the pH dependencies of the guanylyl-3′, 5′-cytidine transesterification reaction of wild type ribonuclease T1 and of the variants, typically bell-shaped curves are observed with a plateau in the range pH 4.5–7.0. Their shapes and slopes indicate that the enzymes are comparable in their macroscopic p K a , values. At pH 7.5, the variant Tyr45Trp&​sol;Trp59Tyr shows a more than 3-fold higher transesterification activity for guanylyl-3′, 5′-adenosine and a 2-fold increase for guanylyl-3′, 5′-cytidine compared to the wild type enzyme, i.e. this variant catalyses the transesterification of the substrate guanylyl-3′, 5′-adenosine with the same or better efficiency as guanylyl-3′, 5′-cytidine.
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  • Copyright (C) 1993, Oxford University Press
Language
  • English
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