title: An essential tryptophan in the active site of phospholipase A2 from the venom of Bitis gabonica.
abstract: The role of tryptophan in phospholipase A2 (EC 3.1.1.4) from the venom of the gaboon viper, Bitis gabonica, has been investigated. Modification of the enzyme with N-bromosuccinimide and 2-nitrophenylsulfenylchloride showed that the two tryptophan residues in the enzyme, viz. Trp-28 and Trp-59, differ in reactivity towards the reagents. Only Trp-28 reacted with N-bromosuccinimide while a preferential reaction occurred between Trp-59 and 2-nitrophenyl-sulfenylchloride. In each case it was found that loss of enzyme activity was specifically correlated with modification of TRP-28. CD spectra indicated that neither the local nor the gross conformation of the enzyme was altered by modification of Trp-28 and it was therefore concluded that Trp-28 is crucial for enzyme activity. The active enzyme was protected against N-bromosuccinimide inactivation by micellar concentrations of substrate or substrate analogue, suggesting that Trp-28 is involved in substrate binding.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001665:Binding Sites; D002918:Chymotrypsin; D002942:Circular Dichroism; D003488:Cyanogen Bromide; D004229:Dithiothreitol; D007461:Iodoacetates; D010446:Peptide Fragments / Q000032:analysis; D010740:Phospholipases; D011485:Protein Binding; D011487:Protein Conformation; D012910:Snake Venoms; D014364:Tryptophan / Q000032:analysis
chemical_list: D000596:Amino Acids; D007461:Iodoacetates; D010446:Peptide Fragments; D012910:Snake Venoms; D014364:Tryptophan; D010740:Phospholipases; D002918:Chymotrypsin; D003488:Cyanogen Bromide; D004229:Dithiothreitol