Characterization of the amino acids essential for the photo- and radioprotective effects of a Bowman-Birk protease inhibitor-derived nonapeptide

The Bowman-Birk protease inhibitor has been reported to exert photo- and ra dioprotective activity. This effect was assigned to a cyclic nonapeptide se quence which is known to contain the amino acids responsible for the anti-c hymotryptic activity of the BBI, The present study indicated that lineariza tion of the nonapeptide resulted in a significant loss of anti-proteolytic activity, whereas the photo- and radioprotective capacity persisted. Substi tution of the amino acids Leu or Ser of the nonapeptide, essential for the anti-proteolytic activity, with different amino acids,indicated that rather the hydrophobic features of the amino acids in this position than charge a re critical to retain the photo- and radioprotective effect. These results suggest the existence of a bifunctional peptide sequence with antiproteolyt ic and photo-/radioprotective capacity. However, the lack of correlation be tween the photo-/radioprotective activity and the anti-proteolytic activity within the peptides generated by modification of the linear nonapeptide ar gues for the existence of two closely colocalized domains within the nonape ptide responsible for photo-/radioprotection and protease inhibition.