A protein was purified to homogene-ity. Determination of the mass by gel- filtration chromatography yields 60 kd. Chromatography in the presence of 6 M urea yields a 30- kd species. When the chromatography is repeated in the presence of 6 M urea and 10 mM – mercaptoethanol, a sin-gle molecular species of 15 kd results. Describe the structure of the molecule.
