Batlle A, Grinstein M. [19] Preparation of porphobilinogen. Metabolism of Amino Acids and Amines Part A. Elsevier; 1970. pp. 220-2. [DOI: 10.1016/0076-6879(71)17184-4]

Amiodarone is a pharmacologically safe drug for porphyrias

Amiodarone (AD) is an effective antidysrythmic drug, however, there can be serious side effects, such as hepatic and neurological alterations, as well as skin photosensitization, as seen in porphyrias. Clinical signs in porphyrias might be triggered by the so-called porphyrinogenic drugs. Without sound basis, Amiodarone has been classified as an unsafe drug for porphyric patients. The aim of this work has been to study the effect of AD, both in vivo and in vitro, on heme metabolism. In the in vivo assays, the activities of 5-aminolevulinate synthetase (ALA-S), ALA dehydratase (ALA-D), porphobilinogenase (PBGase) and PBG-deaminase (PBG-D) in blood, liver, and kidney; hepatic and fecal porphyrins, urinary ALA, PBG and porphyrins in male mice strain CF1 treated with AD (100 mg i.p. daily) for 1 week and 1 month, were measured. No significanat differences were found for any of these parameters in the AD treated animals as compared to controls. In the in vitro experiments human blood, and mice blood, liver, and kidney, were used to measure the activities of ALA-S, ALA-D, PBGase, PBG-D and uroporphyrinogen decarboxylase, in the presence of varying concentrations of AD (0.0172-4.304 mM). AD did not modify any of the enzyme activities. All of the above biochemical parameters were studied in 17 cardiac patients under AD treatment for 3 to 20 years. Neither the activities of the heme enzymes, nor the levels of precursors and porphyrins in urine and plasma were altered. These findings clearly demonstrate that AD is a pharmacologically safe drug and can be used for the treatment of associated pathologies in porphyrias.

Rat harderian gland porphobilinogen deaminase: characterization studies and regulatory action of protoporphyrin IX

Properties of purified porphobilinogen deaminase (PBG-D; EC 4.3.1.8) from rat harderian gland are here presented. The enzyme behaves as a monomer of Mr 38 +/- 2 kDa and is optimally active at pH 8.0-8.2. Its activation energy, determined by an Arrhenius plot, is 76.1 kJ/mol. Initial velocity studies showed a linear progress curve for uroporphyringen I formation and a hyperbolic dependence of the initial rate on substrate concentration, indicating the existence of a sequential displacement mechanism. Apparent kinetic constants, Km and Vm, calculated at 37 degrees C and pH 8.0 were 1.1 microM and 170 pmol/min mg, respectively. The pH dependence of the apparent kinetic parameters revealed the ionization of residues with pKAES and pKBES of 7.4 +/- 0.1 and 8.6 +/- 0.1, respectively, and a pKE value of 8.0 +/- 0.1. Incubation of PBG-D with 5.0 mM N-ethylmaleimide and 5.0 mM 5,5'-dithiobis(2-nitrobenzoic acid) at pH 8.0 led to inhibitions of 70 and 50%, respectively. The effect of pH, as well as the effect of thiol reagents, on enzyme activity strongly suggests the involvement of cysteine residue(s) in the mechanism of uroporphyrinogen I biosynthesis, in both the catalytic reaction and the substrate binding. Rat harderian gland PBG-D activity decreased with increasing concentrations of protoporphyrin IX, reaching a 40% inhibition at the in vivo concentration of the porphyrin and 7 microM PBG. Even at saturating concentrations of substrate, inhibition by protoporphyrin was not completely reversed. So, accumulated porphyrin may act as an regulator of PBG-D activity in rat harderian gland.

Synthesis of the pyrrole porphobilinogen by sepharose-linked -aminolevulinic acid dehydratase

delta-Aminolevulinic acid dehydratase from Rhodopseudomonas spheroides was covalently linked to Sepharose 4B, which had been activated with cyanogen bromide. A column containing this enzyme gel readily catalyzed the synthesis of the pyrrole porphobilinogen on continuous passage of a solution of delta-aminolevulinic acid. Under the conditions of the procedures, product inhibition was minimized and a 50 to 94 percent yield was attained. A column containing about 1 milligram of enzyme was continuously operated for 27 days. Although its total activity appeared to be reduced about 30 percent at the end of this time, the bound enzyme produced approximately 200 milligrams of porphobilinogen each day, and about 5 grams of the pyrrole were isolated.