lac repressor: 3-fluorotyrosine substitution for nuclear magnetic resonance studies.

This paper describes the isolation of 3-fluorotyrosine-substituted lac repressor, and its 19F nuclear magnetic resonance spectrum. From the spectrum, one can conclude that for each of the four identical subunits of the repressor there are four or five surface tyrosines, two buried or internal tyrosines, and one tyrosine with an phenolic group ionized or involved in a hydrogen bond. Conditions are described that can be used for the 3-fluorotyrosine substitution of a variety of Escherichia coli proteins for 19F nuclear magnetic resonance studies.