Trinitrophenylation of bovine growth hormone

Bovine growth hormone was chemically modified with picryl sulfonic acid, at pH 8.4 during 2 and 5 min of reaction. The N-terminal residue provides the most reactive amino group followed by the epsilon-amino groups of lysine 179 and lysines 143, 69, 111, 170 and 166 in decreasing order. These results agree with those obtained previously with equine growth hormone, except that residue 156 is not modified in bovine growth hormone. An important decrease in biological activity occurs between 2 and 5 min of reaction without sensible modification in the alpha-helix content of the molecule.