Evidence for the steric proximity of Tyr 174 and Lys 111 in bovine growth hormone

Bovine growth hormone was modified by reaction with 1,5-difluoro-2,4-dinitro-benzene under conditions favouring production of intramolecularly crosslinked derivatives from monomeric molecules. The monomeric fraction, isolated by chromatography on Sephadex G-100, was oxidized or reduced and carbamido-methylated and trypsin digested. The resulting peptides were fractionated on SP-Sephadex and further purified by peptide mapping or HPLC. Two modified peptides containing sequences 108–112 or 108–113 and 171–176 of bGH were obtained, including a dinitrophenylene bridge between lysine 111 and tyrosine 174, thus suggesting the stereochemical proximity of these residues.