NADH photo-oxidation is enhanced by a partially purified λ-crystallin fraction from rabbit lens

Masayasu Bando, Mikako Oka, Kenji Kawai, Hajime Obazawa, Makoto Takehana

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Purpose: In the rabbit lens, high levels of reduced nicotinamide adenine dinucleotide (NADH) can function as a near-ultraviolet light (near-UV) filter, an effect apparently achieved by specific nucleotide binding to λ-crystallin. The present investigation asks whether λ-crystallin enhances NADH photo-oxidation by superoxide radicals produced via a photosensitization reaction of near-UV with NADH. Methods: λ-Crystallin was partially purified from rabbit lens soluble fraction by a two-step gel filtration and affinity column chromatography procedure. NADH solutions with or without partially purified λ-crystallin were subjected to near-UV irradiation or exposed to superoxide generated enzymatically by the xanthine/xanthine oxidase system. NADH oxidation was determined by assaying the decrease of absorbance at 340 nm. Results: When irradiated with near-UV, free NADH was oxidized very little in the absence of λ-crystallin. In contrast, NADH photo-oxidation was rapidly initiated in the presence of partially purified λ-crystallin. This λ-crystallin-enhanced NADH photo-oxidation was totally inhibited by adding superoxide dismutase. We also found that λ-crystallin largely increased NADH oxidation by a superoxide that is generated enzymatically. These results indicate that NADH bound to λ-crystallin rapidly reacts with superoxides. The reactivity of bound NADH with superoxide was almost equivalent to that of ascorbic acid. However, λ-crystallin-enhanced NADH oxidation exceeded the superoxide levels generated by NADH photosensitization and xanthine/xanthine oxidase. Conclusions: We conclude that NADH binding to λ-crystallin enhances NADH photo-oxidation through a radical chain reaction mechanism that is initiated by superoxides generated by NADH photosensitization and propagated by another superoxide from the molecule oxygen. High concentrations of NADH bound to λ-crystallin may be beneficial to the rabbit lens in scavenging the low amounts of superoxide produced by near-UV absorption, since oxygen tension in the lens is very low. We also discuss the function of near-UV-filtering and the anti-photo-oxidation systems in other vertebrate lenses.

元の言語English
ページ(範囲)1722-1729
ページ数8
ジャーナルMolecular vision
13
出版物ステータスPublished - 2007 9 18

ASJC Scopus subject areas

  • Ophthalmology

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    Bando, M., Oka, M., Kawai, K., Obazawa, H., & Takehana, M. (2007). NADH photo-oxidation is enhanced by a partially purified λ-crystallin fraction from rabbit lens. Molecular vision, 13, 1722-1729.