High-pressure liquid chromatographic resolution of vitamin A compounds

An electrochemical system has been devised to measure phenol concentrations in aqueous solutions. The unit employs the immobilized enzyme, tyrosinase, to oxidize phenol in the presence of saturating levels of oxygen. The oxidation product, ortho-benzoquinone, is then chemically reduced in the presence of an excess of ferrocyanide ions. The coupled oxidation of ferrocyanide ions to ferricyanide ions results in a measurable potential difference in the electrochemical system. The resulting zero current potentials in these steady-state potentiometric measurements are shown to be directly proportional to the logarithm of phenol concentration over the range of 3.8 × 10^?7 to 1 × 10^?4m. The results of studies carried out with alternate substrates for the enzyme and interfering compounds are also presented.     

Liquid-gel partition chromatography of vitamin A compounds; formation of retinoic acid from retinyl acetate in vivo

A clear separation of retinol, retinal, and retinoic acid has been achieved by liquid-gel partition chromatography on Sephadex LH-20 with solvent mixtures of chloroform, Skellysolve B, and methanol. A mixture of retinyl esters, retinol, retinal, and retinoic acid has been resolved on hydroxyalkoxypropyl Sephadex using Skellysolve B and acetone. There is no decomposition of any of the vitamin A compounds during chromatography, and recovery is complete. The combination of mildness and potential for resolution makes liquid-gel partition chromatography a superior tool for the separation of vitamin A compounds. This method has been applied to the study of vitamin A metabolism at physiological levels in the vitamin A-deficient rat. Retinyl palmitate, an ester of retinoic acid, retinal, retinol, retinoic acid, and a polar metabolite have been demonstrated in various tissues of the rat 12 hr after a dose of 2 micro g of [11-(14)C]retinyl acetate.     

Rapid actions of vitamin D compounds.

The rapid actions of vitamin D compounds are surveyed in a variety of target tissues, including intestine, muscle, bone, hepatocytes, fibroblasts, HL-60 cells, kidney, mammary gland, and parathyroid. Evidence for non-nuclear receptors vs. membranophilic effects is discussed, followed by a consideration of signal transduction mechanisms including steroid hormone activated Ca2+ channels, phospholipid metabolism, protein kinases, and the role of G-proteins.     

Production of high-value compounds: carotenoids and vitamin E

The unraveling in recent years of the pathways and genes that are responsible for biosynthesis of vitamins and carotenoids in plants has provided new molecular tools that can be utilized to genetically modify the content and composition of these compounds in vivo. There have been recent examples of successful manipulation of carotenoid composition and vitamin E activity in plants using gene-transfer technology.