studies on vitamins A1 and A2 and their derivatives

Abstract

Vitamin A, if it were to fulfil most of its systemic functions and exert its biological activity through its acid form, or presumably an active form derived from it, then nature is provided with the necessary mechanisms for the formation of the acid form from the aldehyde form. Consequently, the enzyme responsible for the formation of the acid form may assume greater importance than the enzyme responsible for the formation of the immediate precursor of the acid form, i.e., the aldehyde form, in the active metabolism of vitamin A. The present trend of assaying the biopotency of any vitamin on a particular species and then assuming it to hold good for other species as well may not be universally true. A more rational approach would be to assay the biopotency of the vitamin on a species for which it is natural. Studies on the metabolic transformations of vitamin A indicate that the active form of the vitamin is centred around its more oxidised state. Not only is the oxidation at the terminal side-chain end group effective in maintaining profound biological activity, but so is the oxidation at the -ionone ring of the molecule. As long as the terminal side-chain aldehyde group is available, oxidation at the -ionone ring may not affect the visual function of the vitamin. But it seems that oxidation either at the -ionone ring or in the side-chain end group results in the impairment of the reproductive function of vitamin A, especially in females. Thus, it is very likely that a conjugated system of four double bonds may be an absolute requirement for any vitamin A-like compound to exert its activity. While the aldehyde group is essential for its visual functions, the more oxidised derivative may fulfil its systemic functions. It may well be that oxidation at the -ionone ring makes the molecule more reactive so that vitamin A may take an active part in the multifarious biological functions in which it is implicated.