ABSTRACT
The structure and enzymatic transformations of vitamin A keto-metabolite isolated from the rat liver were investigated. With the aid of physico-chemical methods, using isotopes 3/ and 18O, PMR and mass-spectrometry it was demonstrated that the metabolite was an ester of 4-keto-retinol with palmitic acid. The structure of 4-keto-retinal was confirmed by the chemical synthesis and by the enzymatic production of its derivatives. Under the influence of alcohol dehydrogenase 4-keto-retinol in the presence of NAD transformed into 4-keto-retinal which was oxidized into 4-keto-retinoic acid with the participation ofaldehyde oxidase. Similar oxidative enzymatic transformations occurred with the reduced form of the metabolite--4-hydroxyretinol. All the products were characterized in detail. Metabolism of 4-keto-retinyl-palmitate in vivo is realized via the same pathway as metabolism of retinyl-palmitate. The general pattern of oxidation of beta-ionone ring in position 4 of vitamin A and carotenoids is discussed.
Subject(s)
Liver/metabolism , Vitamin A/metabolism , Alcohol Oxidoreductases , Aldehyde Oxidoreductases , Animals , Biotransformation , Catalysis , Chemical Phenomena , Chemistry , Electron Spin Resonance Spectroscopy , Mass Spectrometry , Rats , Spectrophotometry, Ultraviolet , Vitamin A/analogs & derivatives , Vitamin A/isolation & purificationABSTRACT
Vitamin A metabolites were studied in the liver of white mice, hamsters, guinea-pigs and rabbits after a single administration of retinyl acetate per os. In addition to retinol and retinyl palmitate, the mouse showed retinaldehyde which accumulated in the liver in the maximum concentration 3 hours later after the vitamin administration. Retinaldehyde isolated on aluminium oxide by means of TCA was examined with respect to absorption spectra in the UV-light, NaBH4 reduction with subsequent isolation of anhydrovitamin A from the reduced product as well as to absorption peaks in reactions with SbCl3 and thiobarbituric acid.
