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STRUCTURE AND STABILITY OF γ‐CRYSTALLINS‐V. COVALENT AND NONCOVALENT PROTEIN‐PROTEIN INTERACTIONS IN PHOTOSENSITIZED REACTIONS
Author(s) -
Kono Masahiro,
Mandal Krishnagopal,
Chakrabarti Bireswar
Publication year - 1988
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.1751-1097.1988.tb08849.x
Subject(s) - chemistry , covalent bond , iodoacetamide , dithiothreitol , non covalent interactions , crystallin , sodium dodecyl sulfate , polymerization , polyacrylamide gel electrophoresis , gel electrophoresis , chromatography , cysteine , photochemistry , organic chemistry , hydrogen bond , molecule , biochemistry , enzyme , polymer
— Irradiation of γ‐crystallins with 300 nm light or with the photosensitizers riboflavin or methylene blue (MB) leads to intermolecular cross‐linking and insolubilization. Sodium dodecyl sulfate polyacrylamide gel electrophoresis studies reveal that these cross‐links are composed of nondisulfide covalent bonds. The water‐insoluble phase is stabilized by noncovalent forces, as denaturants readily dissolve it. High‐performance liquid chromatography and electrophoresis results further indicate that the higher multimers are part of this water‐insoluble fraction only, with the exception of MB‐sensitized reactions, which are also able to produce a water‐soluble, high‐molecular‐weight protein of at least 1 million. Labeling the external sulfhydryl groups with iodoacetamide does not prevent the photoreac‐tions; however, a reducing agent such as dithiothreitol does. A mechanism involving initial oxidation and interaction of sulfhydryl groups (forming an intramolecular disulfide) buried within the protein as a necessary precursor to polymerization and precipitation has been proposed in the preceding paper. The present study provides support for this mechanism.