Heme Biosynthesis in Intermittent Acute Porphyria: Decreased Hepatic Conversion of Porphobilinogen to Porphyrins and Increased Delta Aminolevulinic Acid Synthetase Activity
01 Nov 1970-Proceedings of the National Academy of Sciences of the United States of America (National Academy of Sciences)-Vol. 67, Iss: 3, pp 1315-1320
TL;DR: A micro-radio-chemical assay of delta-aminolevulinic acid synthetase, and some of its applications, are described, and this first and rate-controlling enzyme in the biosynthetic pathway is subject to negative feedback regulation by the end product, heme.
Abstract: Hepatic conversion of porphobilinogen to porphyrins was less than 50% of control levels in human subjects with the genetic disease, intermittent acute porphyria. This relative block in heme biosynthesis may be relevant to a concomitant 6- to 10-fold elevation in δ-aminolevulinic acid synthetase activity, since this first and rate-controlling enzyme in the biosynthetic pathway is subject to negative feedback regulation by the end product, heme. A micro-radio-chemical assay of δ-aminolevulinic acid synthetase, and some of its applications, are described.
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TL;DR: It is proposed that porphyria cutanea tarda results from the combination of an inherited defect in uroporphyrinogen decarboxylase and an acquired factor, usually siderosis associated with alcoholic liver disease.
Abstract: Uroporphyrinogen decarboxylase activity was measured in liver and erythrocytes of normal subjects and in patients with porphyria cutanea tarda and their relatives. In patients with porphyria cutanea tarda, hepatic uroporphyrinogen decarboxylase activity was significantly reduced (mean 0.43 U/mg protein; range 0.25-0.99) as compared to normal subjects (mean 1.61 U/mg protein; range 1.27-2.42). Erythrocyte uroporphyrinogen decarboxylase was also decreased in patients with porphyria cutanea tarda. The mean erythrocyte enzymatic activity in male patients was 0.23 U/mg Hb (range 0.16-0.30) and in female patients was 0.17 U/mg Hb (range 0.15-0.18) as compared with mean values in normal subjects of 0.38 U/mg Hb (range 0.33-0.45) in men and 0.26 U/mg Hb (range 0.18-0.36) in women. With the erythrocyte assay, multiple examples of decreased uroporphyrinogen decarboxylase activity were detected in members of three families of patients with porphyria cutanea tarda. In two of these families subclinical porphyria was also recognized. The inheritance pattern was consistant with an autosomal dominant trait. The difference in erythrocyte enzymatic activity between men and women was not explained but could have been due to estrogens. This possibility was supported by the observation that men under therapy with estrogens for carcinoma of the prostate had values in the normal female range. It is proposed that porphyria cutanea tarda results from the combination of an inherited defect in uroporphyrinogen decarboxylase and an acquired factor, usually siderosis associated with alcoholic liver disease.
258 citations
TL;DR: Evidence is provided that decreased activity of heme synthetase is the basic defect in the heme synthetic pathway in protoporphyria, which is probably responsible for protoporphyrin accumulation and hence the biochemical and clinical features observed in prophyria.
Abstract: The final step in heme biosynthesis is chelation of porphyrin with Fe++ catalyzed by the mitochondrial enzyme heme synthetase. We have employed a sensitive radiochemical assay for this enzyme, using 59Fe and deuteroporphyrin or protoporphyrin as substrates. In this method iron is maintained in the ferrous state, oxygen is excluded from the incubation system, and labeled heme product is extracted into ethyl acetate. This assay has been used to measure the activity of heme synthetase in homogenates of liver, obtained by needle biopsy, and in sonicates of human skin fibroblasts, cultured in vitro. In addition, activity of the first enzyme of the heme synthetic pathway, delta-aminolevulinic acid synthetase, has been measured in fibroblast lysates. Lysates of fibroblasts from eight patients with protoporphyria had activities of delta-aminolevulinic acid synthetase which did not differ significantly from those of eight normal fibroblast lines, whereas activity of heme synthetase, with either deuteroporphyrin or protoporphyrin as substrate, was markedly decreased in sonicates of skin fibroblasts from these patients, the mean being 8% of control with deuteroporphyrin and 14% with protoporphyrin as substrate. In homogenates of liver from five patients with protoporphyria, activity of heme synthetase was also significantly less than that found in six patients without prophyria, the mean being 13% of control with protoporphyrin as substrate. These results provide evidence that decreased activity of heme synthetase is the basic defect in the heme synthetic pathway in protoporphyria. This deficiency is probably responsible for protoporphyrin accumulation and hence the biochemical and clinical features observed in protoporphyria.
217 citations
TL;DR: In a family with intermittent acute porphyria five affected members were found to have decreased erythrocyte uroporphyrinogen I (URO)-synthetase activity, when compared to unaffected members.
Abstract: In a family with intermittent acute porphyria (IAP) five affected members were found to have decreased erythrocyte uroporphyrinogen I (URO)-synthetase activity, when compared to unaffected...
197 citations
TL;DR: In a patient with a severe attack of acute intermittent porphyria, hematin given intravenously caused marked diminution of serum delta-aminolevulinic acid and porphobilinogen.
Abstract: In a patient with a severe attack of acute intermittent porphyria, hematin given intravenously caused marked diminution of serum δ-aminolevulinic acid and porphobilinogen. The decline of aminolevulinate was more rapid than that of porphobilinoge. After 2 days of hematin administration, about 5 days were required for δ-aminolevulinic acid, and 11 days for porphobilinogen to return to the concentrations that were detected before treatment. Urinary excretion of both compounds also decreased after hematin administration. Considerable amounts of porphobilinogen were also found in the cerebrospinal fluid of the patient.
171 citations
TL;DR: Fecal protoporphyrin is increased in patients with variegate porphyria, even during clinical remission, suggesting an enzymatic defect in the terminal portion of the heme biosynthetic path.
Abstract: Fecal protoporphyrin is increased in patients with variegate porphyria, even during clinical remission, suggesting an enzymatic defect in the terminal portion of the heme biosynthetic path...
141 citations