STUDIES IN PORPHYRIA .6. BIOSYNTHESIS OF PORPHYRINS IN MAMMALIAN SKIN AND IN SKIN OF PORPHYRIC PATIENTS

[摘要] Porphyrin biosynthesis in mammalian skin and in skin obtained from patients with selected types of porphyria was studied. Cutaneous porphyrinogenesis required the precursor .delta.-aminolevulinic acid (ALA) which, when added to murine, rat, and human skin in vitro, was rapidly converted to porphyrins. Total porphyrin content was quantitated by fluorescence assay, and spectral studies indicated that more than 80% of the porphyrin produced was protoporphyrin. The majority of skin porphyrinogenesis occurred in epidermis or in epidermal derivatives such as hair roots. Known inducers of hepatic .delta.-aminolevulinic acid synthetase (ALAS), the rate-limiting enzyme for heme biosynthesis, were not inducers when added to skin in vitro. Skin from patients with acute intermittent porphyria demonstrated a 43% decrease in cutaneous porphyrin production as compared to unaffected normals. This is consistent with the known deficiency of uroporphyrinogen synthetase that was previously demonstrated in the liver and red blood cells of these patients. Porphyrinogenesis in skin of patients with porphyria cutanea tarda was not different from controls. Skin has the enzymatic capacity to synthesize porphyrins from added ALA and cutaneous porphyrinogenesis from ALA is deficient in patients with acute intermittent porphyria.