Abstract
The photoproduction of vitamin D in the skin was essential for the evolutionary development of terrestrial vertebrates. During exposure to sunlight, previtamin D3 formed in the skin is isomerized to vitamin D3 (calciol) by a temperature-dependent process. Since early land vertebrates were poikilothermic, the relatively slow conversion of previtamin D3 to vitamin D3 at ambient temperature put them at serious risk for developing vitamin D deficiency, thus leading to a poorly mineralized skeleton that could have ultimately halted further evolutionary development of vertebrates on land. We evaluated the rate of isomerization of previtamin D3 to vitamin D3 in the skin of iguanas and found the isomerization rate was enhanced by 1100% and 1700% at 25 degrees C and 5 degrees C, respectively. It is likely that the membrane entrapment of previtamin D3 in its s-cis,s-cis conformation is responsible for the markedly enhanced conversion of previtamin D3 to vitamin D3. The membrane-enhanced production of vitamin D3 ensures the critical supply of vitamin D3 to poikilothermic animals such as iguanas.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Holick M. F., MacLaughlin J. A., Clark M. B., Holick S. A., Potts J. T., Jr, Anderson R. R., Blank I. H., Parrish J. A., Elias P. Photosynthesis of previtamin D3 in human skin and the physiologic consequences. Science. 1980 Oct 10;210(4466):203–205. doi: 10.1126/science.6251551. [DOI] [PubMed] [Google Scholar]
- Holick M. F., MacLaughlin J. A., Doppelt S. H. Regulation of cutaneous previtamin D3 photosynthesis in man: skin pigment is not an essential regulator. Science. 1981 Feb 6;211(4482):590–593. doi: 10.1126/science.6256855. [DOI] [PubMed] [Google Scholar]
- Tian X. Q., Chen T. C., Lu Z., Shao Q., Holick M. F. Characterization of the translocation process of vitamin D3 from the skin into the circulation. Endocrinology. 1994 Aug;135(2):655–661. doi: 10.1210/endo.135.2.8033813. [DOI] [PubMed] [Google Scholar]
- Tian X. Q., Chen T. C., Matsuoka L. Y., Wortsman J., Holick M. F. Kinetic and thermodynamic studies of the conversion of previtamin D3 to vitamin D3 in human skin. J Biol Chem. 1993 Jul 15;268(20):14888–14892. [PubMed] [Google Scholar]
- Yamamoto J. K., Borch R. F. Photoconversion of 7-dehydrocholesterol to vitamin D3 in synthetic phospholipid bilayers. Biochemistry. 1985 Jun 18;24(13):3338–3344. doi: 10.1021/bi00334a039. [DOI] [PubMed] [Google Scholar]