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J Bacteriol. 1972 July; 111(1): 163-168
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Comparative Immunological and Enzymatic Study of the Tryptophan Synthetase ß₂ Subunit in the Enterobacteriaceae

Department of Biology, University of California, San Diego, La Jolla, California 92037, and Department of Microbiology, Scripps Clinic and Research Foundation, La Jolla, California 92037

ABSTRACT

The ß₂ subunits of tryptophan synthetase, formula ₂ß₂, from Escherichia coli, Shigella dysenteriae, Enterobacter aerogenes, Salmonella typhimurium, and Serratia marcescens were compared by three criteria. (i) ß association constants for the various ß₂ subunits and E. coli subunit varied between 3.6 x 10⁸M^–1 for E. coli and 0.33 x 10⁸M^–1 for S. marcescens; values for the other organisms were intermediate. (ii) Antiserum neutralization of the ß₂ subunit enzyme activity using anti-E. coli ß₂ 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 ß₂ and S. marcescens ß₂ 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 subunit binding site of the ß₂ subunits from these Enterobacteriaceae have been strongly conserved.

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