SUBCELLULAR SITES OF ZINC IN THE CRYSTALLINE LENS

The location of zinc in aqueous homogenized extracts of rabbit lenses indicated that about 95% of the total present was associated with the supernatant fraction. Gel-filtration of this solution on Sephadex G-200 or Sepharose CL-6B resulted in spectrophotometric identification of 4 or 5 peaks of protein that are expected to include lens crystallins. The zinc present in the supernatant was found to be closely associated with 2 of these peaks that had molecular weights estimated to be 40 kDa (55% of the zinc) and 670 kDa (30% of the zinc). The zinc contained in the associated fractions was not dialyzable against a solution containing 1 mM EDTA at pH 7.4. The zinc-metalloenzymes carbonic anhydrase and superoxide dismutase would not be expected to contribute more than about 10% to the total lenticular zinc, but they may be present in the 40 kDa fraction. Most of the protein-bound zinc in the lens is, thus, unaccounted for and possibly may be associated with lens crystallins.