<原著>ニホンアマガエル(Hyla japonica)水晶体ζ-クリスタリン : ウシガエル(Rana catesbeiana)水晶体ρ-クリスタリンとの比較

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ρ-Crystallin, a taxon-specific crystallin, expressed in the lenses of American Bullfrog (Rana catesbeiana) and Black-spotted Pond Frog (Rana nigromaculata) occupies about 8% of the wet-weight of their tissues. The crystallin belongs to the superfamily of aldo-keto reductases, but shows no enzymatic activity. The present study demonstrates that ζ-crystallin, instead of ρ-crystallin, is expressed in the lens of tree frog (Hyla japonica). ζ-Crystallin is known to be present in the lenses of camel and guinea pig and shows the instrinsic enzymatic activity of quinone reductase (EC 1.6.99.2, NADPH: quinone oxidoreductase). Tree frog lens ζ-crystallin also had the enzymatic activity, and catalyzed the reduction of 9,10-phenanthrenequinone (Km:42μM) using NADPH as a cofactor, and was strongly inhibited by dicumarol, anti-coagulant drug, with IC_<50> of 4μM. The crystallin consisted of 38 kDa subunits did not cross-react with anti-ρ-crystallin antibodies. During ρ-crystallin molecular evolution, the crystallin probably has lost the aldo-keto reductase activity to avoid the development of diabetic complications such as cataract. On the other hand, the overproduction of ζ-crystallin with intrinsic enzymatic activity in lens does not affect the physiological functions of the tissue. It is interesting that NADPH-binding ability is conserved in the both crystallins. Because NADPH efficiently absorbs near-ultraviolet light, the nucleotide may protect retina from the toxicity caused by the near-UV irradiation. There is a possibility that NADPH-binding ability of the both crystallins contributes to maintain the high concentration of NADPH in the lenses. In the present study, the analysis of taxon-specific crystallin led to the finding of ρ-crystallin in the lens of tree frog and this approach may be available for the biochemical classification of many other animals in addition to frogs and toads.
2000-06-30

<原著>ニホンアマガエル(Hyla japonica)水晶体ζ-クリスタリン : ウシガエル(Rana catesbeiana)水晶体ρ-クリスタリンとの比較

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