The occurrence of vitamin A in biological membranes

Abstract 1. 1. Rats maintained on a low vitamin A intake were intraperitoneally injected with 50.7 μg [11,12- 3 H 2 ]retinyl acetate. 15 h later, the animals were killed and liver and kidney plasma membranes, kidney endoplasmic reticulum and erythrocyte ghosts were prepared. 2. 2. The labeled vitamin A content of the membrane preparations varied consistently between 0.003–0.005 μg retinol/mg N, while the level in the homogenate varied from 0.001–0.009 μg retinol/mg N. The labeled vitamin A content of the erythrocyte ghosts was low (max. 0.0001 μg retinol/mg N) probably due to heavy hemoglobin contamination. 3. 3. The radioactive vitamin A compounds were strongly bound to the membranes: n- hexane removed only 7% of the radioactive compounds, whereas chloroform-methanol (2:1, v/v) extraction of the membrane preparations removed 90% of the radioactive compounds. 4. 4. Thin-layer chromatography of the chloroform-methanol (2:1, v/v) extract of the kidney endoplasmic reticulum, in three different solvent systems, revealed that retinol and retinoic acid were the dominant forms of vitamin A. This was confirmed by combined column and thin-layer chromatography (using a fourth solvent system) of the chloroform-methanol (2:1, v/v) extract of endoplasmic reticulum.