Nature of the provitamin D of the ribbed mussel, Modiolus demissus (Dillwyn).

Since 1934, when it was shown that ergosterol is not the only provitamin D occurring in nature (l), the provitamin D content of the mixed sterols from many sources has been investigated (2-6). It has been found that the sterols from many of the invertebrates contain a surprisingly large amount of provitamin D as measured spectroscopically. Windaus (3) and Bock and Wetter (4) were able to isolate, in certain cases, a provitamin D fraction sufficiently pure for identification a.nd they always obtained either ergosterol or 7-dehydrocholesterol. Boer et al. (7, 8) described the preparation of provitamin-containing sterols from several invertebrate sources and claimed that, on irradiation, these sterols yield a vitamin D which is highly efficacious when tested on chicks. These workers also described the purified provitamin sterol from selected sources, particularly the edible mussel, Mytilus e&&s, and the periwinkle, Littorina littorea. The physical and chemical constants given for these provitamin fractions indicated that they were different from known sterols, but the fact was not thoroughly excluded that they were mixtures. More recently van der Vliet (9, 10) reported a detailed study of Mytilus provitamin D and concluded that it was a mixture. While none of the components was isolated in pure form, on the basis of fractionation procedures, degradation, and biological efficacy of certain fractions he concluded that the provitamin mixture consisted of approximately 50 per cent 7-dehydrocholesterol, 17 per cent ergosterol, and nearly 33 per cent of a third provitamin tentatively identified as 22-dehydro-7-dehydrocholesterol (A68 ‘9 22-cholestatrien-3-01). In addition, there was evidence of a small amount of an unidentified fourth component. Prior to World War II the mixed sterols of M. edulis were developed in Holland as a commercial source of provitamin D. Large quantities of these sterols were imported by the du Pont company during the period 193840 and irradiated with ultraviolet light to yield vitamin D preparations for use particularly in poultry and animal feeds. Thus we had an opportunity of learning the provitamin D content of these sterols and, after careful irradiation, the yield and biological efficacy of the vitamin D