Topography of Escherichia coli ribosomal protein L12 in situ.

The ionization constants of each individual free amino group of Escherichia coli ribosomal protein L12 as it exists on the native intact 50-S subunit has been determined. All these amino groups are exposed and have pK values varying from 9.7 to 11.0. The amino terminus, on the other hand, is unreactive and therefore appears to be buried. In addition, the reactivities indicate that the aminoterminal region of residues 1--59 undergoes a pH-dependent conformational change on the 50-S subunit.