Role of Cysteine Residues in the Lac Permease of Escherichia coli

Donald R. Menick, Jonathan A. Lee, H. Ronald Kaback, Robert J. Brooker, T. Hastings Wilson

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


Oligonucleotide-directed, site-specific mutagenesis has been utilized to replace cysteine residues 1 17, 333, or 353 and 355 with serine in the lac permease of Escherichia coli. Replacement of Cys-117 or Cys-333 has no significant effect on permease activity, while permease with serine residues in place of Cys-353 and Cys-355 has about 50% of wild-type permease activity. The results provide a clear demonstration that cysteine residues at positions 117, 333, 353, and 355 are not obligatory for lactose/H+ symport. When considered in conjunction with previous findings, the results indicate that, of the eight cysteine residues in the lac permease, only Cys-154 is important for lactose transport. As discussed, the conclusion has important implications for the hypothesis that sulfhydryl—disulfide interconversion plays an important role in the symport mechanism.

Original languageEnglish (US)
Pages (from-to)1132-1136
Number of pages5
Issue number4
StatePublished - 1987
Externally publishedYes


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