[Metabolic fate of porphyrin and its precursors in porphyria and porphyrinuria].

The metabolic fate of porphyrins and its precursors in porphyria and porphyrinuria is discussed to understand their excretion into the feces or urine. Eight enzymes play important roles in the porphyrin pathway. An enzymatic defect at each step of heme synthesis will induce each typical form of porphyria with the exception of the first enzyme. Each porphyria is described according to the enzyme in the heme biosynthetic sequence. Lead, which disturbs two enzymes involved in the heme biosynthesis, is one of typical chemicals inducing porphyrinuria. Lead porphyrinuria is also described according to the enzymes in the pathway. The figure of porphyrin pathway, drawn in details in the present chapter, will make it easier to understand the heme biosynthetic pathway related to porphyria or porphyrinuria.