RT Book, Section A1 Bickers, David R. A1 Frank, Jorge A2 Goldsmith, Lowell A. A2 Katz, Stephen I. A2 Gilchrest, Barbara A. A2 Paller, Amy S. A2 Leffell, David J. A2 Wolff, Klaus SR Print(0) ID 56065730 T1 Chapter 132. The Porphyrias T2 Fitzpatrick's Dermatology in General Medicine, 8e YR 2012 FD 2012 PB The McGraw-Hill Companies PP New York, NY SN 978-0-07-166904-7 LK accessmedicine.mhmedical.com/content.aspx?aid=56065730 RD 2024/03/19 AB The porphyrias are among the most intriguing human diseases. Widely variable, even bizarre in their clinical manifestations, these disorders of porphyrin or porphyrin-precursor metabolism result from aberrations in the control of the heme biosynthetic pathway. Heme is essential for oxygen binding and transport (as in hemoglobin and myoglobin), for electron transport (as in cytochromes), and for monooxygenases such as cytochrome P450. Chlorophyll, a magnesium-chelated porphyrin, is another important tetrapyrrole that is critical for photosynthesis, the specialized energy-storing system found in plants in which the conversion of light energy into stabilized chemical energy is achieved with a sequence of oxidation-reduction reactions. The corrin ring, a cobalt-chelated tetrapyrrole, is a major constituent of vitamin B12, the lack of which results in pernicious anemia. Therefore, porphyrins are ubiquitous and essential biochemical constituents of living beings. The biologic importance of the porphyrins and their iron complexes lies in their capacity to facilitate metabolic reactions, either as oxidative components in the metabolism of steroids, drugs, and environmental chemicals or by enhancing gas exchange, such as oxygen and carbon dioxide, between the environment and the tissues of the body.