Reaction of human chorionic somatomammotropin and human pituitary growth hormone with tetranitromethane at 0 degrees C

The comparative reactivity of the eight tyrosine residues which occur at homologous positions in human chorionic somatomammotropin and human pituitary growth hormone has been investigated by their reaction with tetranitromethane at 0 °C. The derivatives were characterized by circular dichroism spectra, spectrophotometric titrations, rate of tryptic digestion, and immunodiffusion. Pigeon crop-sac stimulating activities were fully retained in these derivatives. The extent of modification for human chorionic somatomammotropin and human pituitary growth hormone was 2.5 and 4.2 out of 8 residues, respectively. The location of each modified tyrosine residue in the derivatives was determined by amino acid analysis of isolated nitrated peptides after cyanogen bromide cleavage and enzymatic digestion. It was found that tyrosine-143 was highly reactive in the pituitary hormone but unreactive in the placental hormone.