There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
Spectrophotometric and radioactive techniques were used to measure the water solubility
of retinaldehyde, retinol (vitamin A), and retinoic acid under physiological conditions.
Hydration decreases the molar extinction coefficient of these substances and shifts
their absorption peak bathochromically (10 nm for retinal and approximately 1 nm for
the rest). We find their solubility to be about 0.1 microM at room temperature, pH
7.3 (with experimental values being 0.11 microM for retinaldehyde, 0.06 microM for
retinol, and 0.21 microM for retinoic acid). To prevent oxidative degradation of retinol,
which is the most labile retinoid, our argon-saturated buffer solutions contained
physiological levels of ascorbate or alpha-tocopherol. To the best of our knowledge,
water solubility of these compounds has not yet been previously reported. Although
the measured solubilities are relatively low, they are significant and may account
for the movement of retinoids through the aqueous phase as observed by others during
exchange with binding proteins and during intervesicular transfer in the absence of
binding proteins. Diffusion of uncomplexed retinoids through the aqueous phase can
be a major pathway for transport over subcellular distances.