Comparative Immunological and Enzymatic Study of the Tryptophan Synthetase β 2 Subunit in the Enterobacteriaceae

Abstract

The β 2 subunits of tryptophan synthetase, formula α 2 β 2 , from Escherichia coli, Shigella dysenteriae, Enterobacter aerogenes, Salmonella typhimurium , and Serratia marcescens were compared by three criteria. (i) αβ association constants for the various β 2 subunits and E. coli α subunit varied between 3.6 × 10 8 m −1 for E. coli and 0.33 × 10 8 m −1 for S. marcescens ; values for the other organisms were intermediate. (ii) Antiserum neutralization of the β 2 subunit enzyme activity using anti- E. coli β 2 serum showed significant cross-reaction among the organisms ( E. coli , 1.0; S. dysenteriae , 0.98; S. typhimurium , 0.67; E. aerogenes , 0.61; S. marcescens , 0.42). (iii) Quantitative microcomplement fixation showed E. coli β 2 and S. marcescens β 2 subunits to have an index of dissimilarity of 1.8 while the other organisms had intermediate indexes. Similar complement fixation data were obtained with antisera from separate rabbits and from first course and boost sera. These findings suggest that the general surface structure and the respective α subunit binding site of the β 2 subunits from these Enterobacteriaceae have been strongly conserved.