The Retinal and 3-Dehydroretinal in Xenopus laevis Eggs are Bound to Lipovitellin 1 by a Schiff Base Linkage(Biochemistry)

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The egg of Xenopus laevis contains both retinal (ret_1) and 3-dehydroretinal (ret_2). The sum of the two retinals and the ratio of the ret_1 to ret_2 in one egg were not so diverse among the eggs in a brood, but the values between different broods varied in the ranges 40-60 pmol/egg and 0.67-1.35, respectively. Both retinals in the egg homogenate were precipitated in 20 mM Tris-HCl buffer, redissolved in NaCl solution at concentrations above 400 mM, and precipitated at 50-65% saturation with ammonium sulfate. The proteins containing retinals corresponded to lipovitellin (LV) on SDS-PAGE. The LV was chromatographed by gel filtration in the presence of SDS into two components, LV1 and LV2, and retinals bound covalently to the binding site by the treatment with sodium borohydride (NaBH_4) were cochromatographed with LV1. The protein with retinals was converted to a fluorescent product by the NaBHt treatment, following which both retinals could no longer be extracted with organic solvents. The fluorescence was observed even after delipidation of the NaBH_4-treated LV. These results indicate that the retinals are bound to the protein moiety of LV1 via a Schiff base linkage. The molar ratio of LV1 to one molecule of ret_1 Or ret_2 was in the range of 12-23. We discuss evidence that the retinals are bound to the lipovitellin precursor, vitellogenin, prior to the uptake of the vitellogenin into the oocyte.
社団法人日本動物学会の論文
1991-10-15