AN ESSENTIAL TRYPTOPHAN RESIDUE OF GREEN CRAB (SYCLLA-SERRATA) ALKALINE-PHOSPHATASE

The, tryptothan residues in green crab (scylla serrata) alkaline phosp hatase (EC 3.1.3.1) have been modified by N-bromosuccinimide (NBS). Th e modification of five tryptophan residues leads to complete loss of e nzymatic activity. With the increase of NBS concentration, both the ab sorption at 278 nm and the fluorescence emission intensity at 335 nm o f the modified enzyme decreased markedly indicating the modification o f tryptophan residues. Quantitative treatment of the data (Tsou, Sci. Sinica 1962, 11, 1535-1558) shows that among the tryptophan residues m odified, one is essential for its catalytic activity. The presence of the substrate markedly protects the modification of tryptophan residue s as well as the inactivation, suggesting that the essential tryptopha n residue is situated at the active site of this enzyme.