Abstract
Photoisomerization of all-trans-retinoic acid and the geo-metrical isomers [9-cis-retinoic acid, 11-cis-retinoic acid, 13-cis-retinoic acid and 9, 13-di-cis-retinoic acid] in ethanol and their biological effects on F9 teratocarcinoma cells were analyzed. The rates of photoisomerization of the retinoic acids illuminated by fluorescent lamps (1, 200 lx) increased in inverse proportion to their concentrations. When the ethanolic solution of all-trans-retinoic acid (10-5 M) was kept under illuminated condition, the equilibrium mixture of the geometrical isomers of retinoic acid [all-trans-retinoic acid 25%, 9-cis-retinoic acid 10%, 11-cis-retinoic acid 10%, 13-cis-retinoic acid 30%, 9, 13-di-cis-retinoic acid 5% and uniden-tified compound 20%] formed at around 30 min. The apparent velocity of the photoisomerization was approximately 8×10-7 mol/L .min. Equi-librium mixtures with similar compositions were obtained by the photo-isomerization of other geometrical isomers. The geometrical isomers produced by the photoisomerization possessed significantly different bio-logical effects in the induction of differentiation of F9 cells into parietal endoderm-like cells: activities of 9-cis-retinoic acid (ED50, 8×10-7 M), 11-cis-retinoic acid (EDS0, 8×10-7 M), and 13-cis-retinoic acid (ED50, 8×10-7 M) were approximately 1/10 of all-trans-retinoic acid (ED50, 8×10-8 M), and activity of 9, 13-di-cis-retinoic acid (ED50, 1×10-5 M) was 1/100 of the level of all-trans-retinoic acid. Further, the retinoic acids acted with each other additively on F9 cells.
