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PROFLAVINE‐SENSITIZED SELECTIVE PHOTOOXXDATION OF THE TRYPTOPHYL RESIDUES IN PAPAIN
Author(s) -
JORI G.,
GALIAZZO G.
Publication year - 1971
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1971.tb06200.x
Subject(s) - chemistry , papain , proflavine , tryptophan , moiety , indole test , molecule , stereochemistry , crystallography , photochemistry , enzyme , amino acid , organic chemistry , biochemistry , dna
— A detailed analysis of the effects of acidic pH values and of temperature on the ultraviolet absorption spectrum of papain demonstrated that the protein can exist in several more or less denatured conformations depending on the surrounding medium. Proflavine‐sensitized photooxidation of papain, under experimental conditions corresponding to the spectroscopically detected conformational states, allowed us to modify separately the five tryptophyl residues. Tryptophan‐7 and 69 appear to be at least partially exposed to the aqueous environment in native papain; however, the former becomes inaccessible to the photooxidizing agent at temperatures lower than 15°C. The photooxidative conversion of these residues to formyl‐kynurenine has no appreciable effect on the tertiary structure as well as on the enzymic activity of papain. On the other hand, tryptophan‐177. which appears to be largely buried, can also be modified with minor variations in the spatial geometry of the protein, but its indole moiety must be critically involved in the enzyme‐substrate interaction, since its conversion to formyl‐kynurenine almost completely inhibits the catalytic activity. Finally, tryptophan‐181 and ‐26 are deeply buried in internal hydrophobic clusters and become available to photooxidation only after the protein molecule has been extensively disorganized. Our results suggest that the solution conformation of some areas of the papain molecule may be different from that in the crystal state as deduced from X‐ray diffraction studies.