156 VITAMIN D GROUP 



chemically. After irradiation, the provitamins of the mealworm, Tenebrio 

 molitor, the sea mussel, Myiilus edulis, the starfish, Asterias rubens, and 

 the sponge, Halychondria panicea, exhibited efficacy ratios of about 100 %, 

 which indicates the absence of much ergosterol. But the activated pro- 

 vitamin of the leech, Hirudo medicinalis, showed only 65 % effectiveness, 

 and that of the crab. Cancer pagurus, only 10 %. These must have contained 

 ergosterol, or some other provitamin of low efficacy ratio. 



The richest of all known animal sources of provitamin D is the ribbed 

 mussel, Modiolus demissus,^^- "^' ^^^ in which the provitamin content 

 amounts to from 35% to 50% of the total sterol. The crude provitamin 

 appears to be a mixture of provitamins D, according to Rosenberg and 

 Waddell,^-° who noted differences in chick-rat efficacy ratios of specimens 

 made from mussels from different environments. From the crude sterols 

 Petering andWaddell ^^ isolated a provitamin which they tentatively called 

 provitamin Dm (m for Modiolus) . This appears to be a single substance, with 

 29 carbon atoms, which in the activated form exhibits an efficacy ratio 

 10 % to 20 % higher than cod liver oil."^ 



5. Biogenesis 



Plants differ from animals in having no mechanism for the translocation 

 of lipoids. Therefore, in plants, the provitamin D, like all sterols, must origi- 

 nate and accumulate in the cells where it is found, whereas in animals its 

 origin may be remote from the site of accumulation. 



In plants ergosterol is the predominant provitamin D. In some of the 

 lower species it comprises up to 95 % of the total sterol, and hence it would 

 seem to be a primary metabolic product. Sumi^^* observed that the forma- 

 tion of ergosterol in the mushroom, Cortinellus shiitake, can occur at any 

 stage of the life cycle, and that the percentage of ergosterol steadily rises 

 i as the plant grows older. 



It would seem that in plants ergosterol is synthesized from simple com- 

 pounds of carbon. Thus ergosterol has been produced in Penicillium glaucum 

 from sucrose and tartaric acid,^^* in Mucor mucedo from lactose, ^^ in Peni- 

 cillium puherulum,^-^ Aspergillus fischeri,^-'^ and many other fungi^-* from dex- 

 trose as the carbon sources. 



123 M. Sumi, Set. Papers Inst. Phys. Chem. Research Tokyo, 20, 254 (1933). 



1" E. Gerard, Coynvt. rend. 114, 1544 (1892). 



126 E. Gerard, Comvt. rend. 121, 723 (1895); ./. pharm. chim. Ser. 6, 1, 601 (1895). 



126 J. H. Birkinshaw, R. K. Callow, and C. F. Fischmann, Biochem. J. 25, 1977 (1931). 



127 L. M. Pruess, W. H. Peterson, and E. B. Fred, /. Biol. Chem. 97, 483 (1932). 



128 L. M. Preuss, W. H. Peterson, H. Steenbock, and E. B. Fred, /. Biol. Chem. 90, 

 369 (1931). 



