VITAMINS

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It is known that biotin deficiency induces both external and skeletal malformations in the embryos of fowl. Also biotin is greatly required for maintaining reproductive function and is contained in a large amount in the egg yolk. Therefore, this study was designed to elucidate the mechanism of biotin transport from hens to eggs and the nutritional magnitude of biotin during ovarian follicular growth. Biotin concentration in ovarian follicles was 87.5±29.3ng/g in the early stage of ovarian follicular growth, which had drastically increased to 674.1±91.4ng/g in the late stage and reached its highest value of 1072.5±197.6ng/g just prior to ovulation. The percentage of free biotin was 75.5±21.1% in the early stage, which had decreased to 28.2±8.8% with the growth of ovarian follicles in the late stage. These values subsequently increased to 73.9±19.2% just prior to ovulation and was 90.9±11.8% in mature egg yolk. These results demonstrate that biotin is stored as "protein binding biotin" from the early to middle stages of ovarian follicular growth and is metabolized to "free biotin" before ovulation, in which a large amount of biotin is transported from hens to eggs. It appears that free biotin is required for maintaining embryonic development soon after fertilization. From these findings, it is suggested that biotin is an essential nutrient and plays an important role in the normal development of embryos in fowls.

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Substantial amounts of vitamin B_<12> were found in some edible algae (green and purple lavers) and algal health food (chlorella and spirulina tablets and so on). Vitamin B_<12>-compounds were purified and characterized from these edible algae to clarify the chemical properties and bioavailability of the algal vitamin B_<12>. True vitamin B_<12> is the predominate cobamide of the eukaryotic algae (green and purple lavers and chlorella sp.). Feeding the purple laver to vitamin B_<12>-deficient rats or humans significantly improved the vitamin B_<12> status. Although these eukaryotic algae consist of both species with or without vitamin B_<12>-requirement, both of them have the ability to take up and accumulate exogenous vitamin B_<12>; there is little information available on physiological function of vitamin B_<12> in the algae. Pseudovitamin B_<12> (an inactive corrinoid compound) predominated in all edible cyanobacteria tested, Spirulina sp., Nostoc commune (Ishikurage), Aphanothece sacrum (Suizenji-nori), and Aphanizomenon flosaquae. They are not suitable for use as a vitamin B_<12> source, especially for vegetarians. Some of these edible cyanobacteria have the ability to de novo synthesize pseudovitamin B_<12>, which can mainly function as the coenzyme of cobalamin-dependent methionine synthase involved in DNA synthesis.

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