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An unusual fluorescence spectrum of a protein proteinase inhibitor, streptomyces subtilisin inhibitor

1976; Elsevier BV; Volume: 453; Issue: 2 Linguagem: Inglês

10.1016/0005-2795(76)90147-1

1878-1454

Yukiko Uehara, Ben’ichiro Tonomura, Keitarō Hiromi, Sakae Sato, Sawao Murao,

Synthesis and Reactivity of Heterocycles

Streptomyces subtilisin inhibitor, a dimeric protein proteinase inhibitor isolated in crystalline form by Murae et al. in 1972, contains three tyrosine and one tryptophan residues per monomer unit and has unusual fluorescence properties. When excited at 280 nm, it shows a characteristic fluorescence spectrum having a peak at 307 nm and a shoulder near 340 nm, a feature which has been recognized only for a very few cases in proteins containing both tyrosine and tryptophan residues. When excited at 295 nm, at which tyrosine scarcely absorbs, the inhibitor shows an emission spectrum with a peak at 340 nm characteristic of a tryptophan residue. The emission with a peak at 307 nm is considered to arise from the tyrosine residues. The tryptophan quantum yield of Streptomyces subtilisin inhibitor excited at 295 nm is very small, indicating that the tryptophan fluorescence is strongly quenched in the native state of the inhibitor. Below pH 4 the peak of the fluorescence spectrum of the inhibitor excited at 280 nm shifts toward 340 350 nm with a concomitant increase in the quantum yield. The structural change induced by low pH seems to release the tryptophan fluorescence from the quenching.