Reaction of ribosomal sulfhydryl groups with 5,5′-dithiobis(2-nitrobenzoic acid)

A. Seetharama Acharya, P. B. Moore

Research output: Contribution to journalArticle

48 Scopus citations

Abstract

The number of sulfhydryl groups in the Escherichia coli ribosome has been measured by titration with 5,5′-dithiobis(2-nitrobenzoic acid). Under denaturing conditions, there are 38.8 ± 1.0 titratable thiols per 70 S ribosome and 22.8 ± 0.3 and 12.9 ± 0.3 titratable thiols per 50 S and 30 S subunits, respectively. Three categories of thiol groups can be distinguished in the native 70 S ribosome, a "fast reacting" class of about 3 residues, a "slow reacting" class of about 10 residues and a "buried" class including about 26 residues. The addition of polyuridylic acid to reaction mixtures protects a fast-reacting thiol in the 30 S subunit belonging to protein S1. The addition of urea to ribosome solutions makes the buried residues titratable. Denaturation occurs as a sharp transition at a urea concentration between 4 and 4.5 m. Urea does not fully dissociate the ribosome into RNA and protein. Instead, in the case of the 30 S subunit, a slowly sedimenting particle forms in the presence of urea, containing roughly 65% of the normal amount of protein.

Original languageEnglish (US)
Pages (from-to)207-221
Number of pages15
JournalJournal of Molecular Biology
Volume76
Issue number2
DOIs
StatePublished - May 15 1973

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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