CHEMICAL MODIFICATION OF OVINE PROLACTIN WITH N-ACETYLIMIDAZOLE

Reaction of ovine prolactin (oPRL) with a 150-fold molar excess of N-a cetylimidazole over protein content resulted in the modification of 2. 5 tyrosine residues and 1.2 lysine residues. Acetylation greatly decre ased the in vitro binding capacity to lactogenic sites. This binding c apacity was partially restored by ammonium bicarbonate treatment, whic h removes O-acetyl groups from tyrosine residues but not N-acetyl grou ps from lysine residues. The modification extent of the tyrosine resid ues was determined. The results suggest that acetylation of tyrosine 4 4 or of tyrosine 96 is likely to be responsible for the decrease in bi nding activity of acetylated oPRL, and that one of these residues may play a role in the interaction of oPRL with lactogenic receptors. (C) Munksgaard 1993.