Abstract
Retinol-binding protein (RBP), isolated from serum of young yellow tail, was distinctly different from mammalian and avian RBPs,, in terms of a lack of binding site for prealbumin on the molecule of piscine RBP, circulating as a monomeric form. Hence, phylogenetic development of serum RBP and intracellular binding proteins for retinoids was also examined: A new molecular species, designated cellular retinoid-binding protein, F-type or CRBP(F), was found initially in fish eye cytosol, later in developing chick embryo brain as well as at a certain stage of regenerating rat liver. Moreover, CRBP(F) was considered to be one of oncofetal proteins, since the protein was detected in human fetal liver as well as in human hepatoma and experimentally induced hepatomas in rats and mice. By means of binding affinity to the receptor protein, a novel polyprenoic acid derivative: 3, 7, 11, 15-tetramethyl-2, 4, 6, 10, 14-hexadecapentaenoic acid was discovered and proved to have antitumor activity in experimental skin papilloma and hepatocarcinogenesis with better therapeutic index than those of previously known synthetic retinoids. Thus, the author has proposed a new naming of "Acyclic Retinoids" for the polyprenoic acid without any aromatic rings in the molecule.
