Porphyrins and the Porphyrias
2008; Elsevier BV; Linguagem: Inglês
10.1016/b978-0-12-370491-7.00008-8
Autores Tópico(s)Neonatal Health and Biochemistry
ResumoThis chapter presents some basic concepts related to porphyrins and the porphyrias. The metal–porphyrin complexes are found widespread in nature as constituents of compounds of fundamental importance in the metabolic processes of life. The photosynthetic pigment of plants, chlorophyll, is a magnesium porphyrin. The iron–porphyrin complexes of animals are found as prosthetic groups of proteins, including the hemoglobins, myoglobins, and the heme enzymes peroxidase, catalase, and the cytochromes. The porphyrins also exist in nature in their free state or as zinc complexes, and it is this group that is associated with the porphyrias and the porphyrinurias. The term porphyria is used to define those disease states that have a hereditary basis with increased urinary or fecal excretion of uroporphyrins and coproporphyrins. Depending on the fundamental biochemical defect, the porphyrias can be broadly classified on the basis of their tissue of origin, the erythropoietic system, or the liver. The term porphyrinuria is used to define those acquired conditions in which the principal porphyrins being excreted are the coproporphyrins. Excess coproporphyrin excretion is observed in a wide variety of conditions including infections, hemolytic anemias, liver disease, and lead poisoning. The screening test for coproporphyrinuria has been especially useful for detecting exposure to lead. This chapter discusses the structure of porphyrins, and also elaborates the synthesis of porphyrins and heme. The chapter concludes with discussing classification of porphyrias, erythropoietic porphyrias, hepatic porphyrias, and porphyrinurias.
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