Heme Biosynthesis and Porphyrin Metabolism

This chapter describes the mechanistic basis of metal-induced alterations in porphyrin metabolism as derived from experimental studies and summarizes the evidence supporting the utility of porphyrin measurements as a biomarker of exposure and effects of specific metals in human subjects, with specific emphasis on lead, mercury, and arsenic. Some perspectives and research needs regarding the use of porphyrin measurements as biomarkers of metal exposures and effects in human populations are also presented. 

The heme biosynthetic pathway, described in Fig. 1, functions in all nucleated cells to provide heme, chlorophyll, and related structures. In mam- 

The remaining steps of the heme biosynthetic pathway, by which coproporphyrinogen is converted to heme, are mediated by three mitochondrial enzymes. Coproporphyrinogen oxidase (EC 1.3.3.3), which is bound to the mitochondrial inner membrane (Elder and Evans 1978), decarboxylates the 

Porphyrin levels as measured in urine samples collected from healthy adult male subjects presenting to this laboratory during the period 1990-1992 for research purposes (Bowers et al. 1992). Values represent the means and standard deviations of 34 individual determinations for 24-h samples and 72 individual determinations for spot samples. 

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