FLAVIN-SENSITIZED PHOTODYNAMIC MODIFICATION OF MULTISUBUNIT PROTEINS

Abstract— Riboflavin 5'-phosphate (FMN)-sensitized photodynamic modifications of multisubunit alcohol dchydrogenase, bacterial luciferase. L-glutamate dehydrogenase, and catalase all lead to significant formation of crosslinked species. On the contrary, irradiation of monomeric lysozyme, trypsin inhibitor, trypsin, and bovine serum albumin in the presence of FMN yields either no or only trace amounts of polymerized molecules. Photodynamic modifications thus appear to be much more efficient in crosslinking proteins with quaternary structures in their native forms. While no photodegradations of other proteins were found, FMN-sensitized modifications of the nonidentical dimeric (αß) bacterial luciferase resulted in the formation of two degraded fragments as well as two polymerized species. Singlet oxygen is shown to be involved in the photopolymerization of luciferase but it is unclear whether singlet oxygen is the sole species active in initiating the crosslinking reaction(s). FMN also sensitizes effective inactivations of luciferase which can be attributed to actions of singlet oxygen, triplet FMN, H₂O₂. and superoxide anion. Photodynamic inactivation of luciferase proceeds faster than photopolymerization; these processes are thus not coupled.