Purification and crystallization of the polypeptide hormone human chorionic somatomammotropin

We have purified the large polypeptide hormone human chorionic somatomammotropin to near electrophoretic homogeneity by a new purification scheme. The hormone crystallized from polyethylene glycol in a form suitable for high resolution x-ray analysis; the crystals are monoclinic, space group C2, a = 123.9, b = 30.3, c = 53.8 A, beta = 119 degrees 30 min, with 1 molecule/asymmetric unit. The growth-promoting activity of homogeneous hormone and of dissolved crystals was measured through their effect on committed erythroid precursor cells in tissue culture assays. Both homogeneous and redissolved crystalline hormone had activities comparable to that of hormone purified by standard procedures. The latter preparations yielded either no crystals, or disordered crystals unsuitable for x-ray analysis.