Effects of riboflavin deficiency on the synthesis of ester forms of riboflavin in the rat lens.

A few reports were found on the riboflavin (B2) in the eye tissues in various species (1-3). Flavin compound in the eye of Rana nigromaculata concentrates in the choroid, iris, ciliary body and is not present in other parts. The amount and distribution of flavin compound in the eye varies considerably in different species of frogs (4). The presence of B2 in the lens of haddock (Gadus aeglefinus), rabbit and other species could not be demonstrated (5). The synthesis of ester forms of B2 in the lenses of various species has not yet been determined, however, it should be noted that flavin-containing enzymes such as glutathione reductase exist in the lens (6, 7). Furthermore, we have reported that ester forms of B2 are synthesized from free riboflavin in the rat lens in vitro as well as in other tissues, and that synthesis of ester forms of B2 is carried out fairly actively (8). In the present study, the changes in formation of ester forms of B2 in the lenses of B2-deficient rats were investigated. Wistar strain male rats weighing about 50-70g were maintained on a B2 deficient diet as reported previously (9). Experiments were carried out at 4 and 8 weeks, respectively, after being fed a B2-deficient diet (Oriental yeast Co., Japan). NADPH-cytochrome c reductase activity (10), glutathione reductase activity (11) and B2 content (12) in the liver, and glutathione reductase activity in the lens (7) were determined as a marker of B2-deficient status. Lenses from excised eyes were carefully removed by the posterior approach and homogenized in 0.1M phosphate buffer (pH 7.5) containing ATP 1mM, MgCl2 1mM and ZnSO4 0.1mM to give a final concentration of 60mg wet weight per ml. Two ml of this homogenate was incubated with 0.02ml of 1.5ƒÊCi/ml D-[2-14C]-riboflavin solution (specific activity 31.0mCi/mmol) for 60min at 37•Ž after which it was