Abstract
Our findings that the apo β 2 subunit of tryptophan synthase of Escherichia coli is inactivated by the modification of one sulfhydryl residue per monomer by nitrothiocyanobenzoic acid and is reactivated by removal of the CN group indicate that the reactive sulfhydryl residue (SH-I) is essential for catalytic activity. SH-I is shown to be the same residue which was previously found to react with bromoacetylpyridoxamine phosphate and different from a sulfhydryl (SH-II) which reacts with N-ethylmaleimide in the presence of pyridoxal phosphate. The results of partial tryptic digestions of β 2 subunit labeled selectively at SH-I or SH-II show that both sulfhydryl residues are located in the F 1 fragment which also contains the pyridoxal phosphate binding site.
Published Version
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