Comparative immunological and enzymatic study of the tryptophan synthetase beta 2 subunit in the Enterobacteriaceae.

The beta(2) subunits of tryptophan synthetase, formula alpha(2)beta(2), from Escherichia coli, Shigella dysenteriae, Enterobacter aerogenes, Salmonella typhimurium, and Serratia marcescens were compared by three criteria. (i) alphabeta association constants for the various beta(2) subunits and E. coli alpha subunit varied between 3.6 x 10(8)m(-1) for E. coli and 0.33 x 10(8)m(-1) for S. marcescens; values for the other organisms were intermediate. (ii) Antiserum neutralization of the beta(2) subunit enzyme activity using anti-E. coli beta(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 beta(2) and S. marcescens beta(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 alpha subunit binding site of the beta(2) subunits from these Enterobacteriaceae have been strongly conserved.