The Properties of Bovine Growth Hormone

The circular dichroism spectrum of bovine growth hormone in the wave length region 250 to 300 nm shows five peaks at 290.5, 284.5, 270, 264, and 258 nm. The longest wave length maximum at 290.5 is assigned to the 1 tryptophanyl residue. The two bands centered at 264 and 258 agree in wave length maxima with the circular dichroism bands of phenylalanyl model compounds. The two remaining peaks, although of opposite sign, are assigned in major part to tyrosyl residues. pH changes in aqueous solution have selective effects on the tryptophanyl and tyrosyl bands, whereas urea modifies them similarly. The phenylalanyl bands survive both extremes of pH and concentrated urea solutions. About half the peptide groups in bovine growth hormone participate in helical structures. In contrast to the important effects that acid and alkali have on the optical activity of the tryptophanyl and tyrosyl chromophores, the peptide dichroic activity is only slightly influenced. Most of the helical residues are, however, randomized in concentrated urea solution.