Immunochemical comparisons of mutant and wild-type α-subunits of tryptophan synthetase

The effects of single and double amino acid substitutions on the tertiary structure of the α-subunit of tryptophan synthetase from Escherichia coli have been investigated by comparing the reactions of mutant and wild-type enzymes with β 2-subunit and with antibodies directed against the wild-type α-subunit. About half the mutants exhibited reduced binding affinities β 2-subunit. In micro-complement fixation assays, however, every mutant reacted with antisera exactly like wild-type. The results suggested that, when present, tertiary structure changes in the mutant proteins tested were limited, possibly to the portions of the surface comprising the active site and the β 2-subunit binding site.