Sensitizer‐induced Conformational Changes in Lens Crystallin—ii. Photodynamic Action of Riboflavin on Bovine Α‐crystallin

Abstract

Abstract— Photolysis of α‐crystallin in the presence of riboflavin under both aerobic and anaerobic conditions causes a rapid decrease in Trp emission; photooxidation most likely occurs via non‐covalent complex formation between the sensitizer molecule and the substrate. However, the change in the tertiary structure of the protein, as manifested in the near‐UV CD, is very different between aerobic and anaerobic photolysis. Riboflavin‐sensitized reaction under aerobic condition causes a major change in the microenvironments of thiol groups as well as in the near‐UV CD, whereas under anaerobic condition the change in the near‐UV CD is much less and SH‐group environments remain unaltered. The sensitizer in this photoinduced change in conformation of the protein is very selective and specific.

Monitoring Light‐induced Changes in Isolated, Intact Eye Lenses

“…2). In reactions involving N-FK as the photosensitizer, active species of oxygen such as lo2, OH', 05 and HzOz are produced, which have been implicated as responsible for protein crosslinking (Walrant and Santus, 1974;Foote, 1976;Saito et al, 1977;Goosey et al, 1980;Zigman;Jori and Spikes, 1981;Grossweiner, 1981;Zigler et al, 1982;Creed, 1984;Dillon, 1984) and also for the changes in protein tertiary structure (Andley et al, 1984;Bose et al, 1985Bose et al, , 1986Mandal et al, 1986). The results in Fig.…”

“…2 indicate that the N-FK undergoes substantial photodegradation and might not accumulate to high levels in the lens. Furthermore, it has been shown recently Bose et al, 1986) in the photosensitized reactions of crystallins that although the sensitizers methylene blue and riboflavin cause a major conformational change in these proteins, N-FK does not. Thus it appears that the photodynamic effects of endogenous N-FK in regard to lens damage might not be as critical as has been thought (Goosey et al, 1980;Goosey, 1981, 1984;Zigler et al, 1982).…”

“…Irradiation of the lens proteins, the crystallins, induces direct or sensitized photooxidation of the constituent tryptophan (Trp)t residues to Nformylkynurenine (N-FK) and other products, some of which have been identified in cataractous or aged lenses (Pirie, 1971;Grover and Zigman, 1972;Walrant and Santus, 1974;Dillon and Spector, 1980;Borkman et al, 1981;Zigler and Goosey, 1981;Liang et al, 1985). The photoinduced structural changes in several of the crystallins have also been documented in the solution state (Fujimori, 1982;Andley et al, 1984;Bose et al, 1985Bose et al, , 1986Mandal et al, 1986;Chakrabarti et al, 1986). We now relate these studies to the whole lens by monitoring in situ photoinduced changes directly in whole lenses isolated from mammalian and avian eyes.…”

Long‐term biomechanical properties of rabbit sclera after collagen crosslinking using riboflavin and ultraviolet A (UVA)

“…Also, the riboflavin was prepared without dextran this time so that the treated sclera was better hydrated. Other important factors that should have an influence on the prevention of retinotoxic effects are scleral thickness and dryness, the degree of saturation of the sclera with riboflavin, blood vitamin C and oxygen level (Bose et al. 1986; De La Rochette et al.…”

“…The observed biomechanical effect is caused by a photodynamic process involving the photosensitizer riboflavin (absorption peak around 370 nm) and UVA light of 370 nm. The riboflavin-sensitized UVA photoreaction generates free radicals and so-called reactive oxygen species (ROS) like superoxide anion (O 2 )), hydroxyl radical (·OH) or hydrogen peroxide (H 2 O 2 ) mainly via the so-called type I pathway of photosensitized oxidation (Bose et al 1986), which induce crosslinking of the collagen type I molecule chains leading to a significantly increased molecular weight. The aggregation of collagen is at least partially caused by the formation of dityrosine (Kato et al 1994).…”