delta-Aminolevulinic acid dehydratase inactivation by uroporphyrin I in light and darkness.

1. The action of uroporphyrin I on erythrocytic ALA-D activity under dark and light conditions was examined. 2. Photo and non-photoinactivation of ALA-D induced by uroporphyrin I were observed. 3. Both effects were dependent on uroporphyrin concentration, temperature and time of exposure of the protein to the porphyrin. 4. Light-dependent effect of uroporphyrin I is related with the phototoxicity of porphyrins and could be produced by primary amino acid photooxidation followed by secondary cross-linking of the protein. 5. Light-dependent effect of uroporphyrin I could be ascribed to a direct enzyme inhibition due to binding of the porphyrin to the protein inducing structural changes at or near its active site.

How the atmosphere and the presence of substrate affect the photo and non-photoinactivation of heme enzymes by uroporphyrin I.

1. The effect of URO I on the activity of ALA-D, PBGase, deaminase and URO-D, both in aerobiosis and anaerobiosis, was studied. 2. Photoinactivation of the enzymes was much lower in an anaerobic than in an aerobic atmosphere. 3. Dark inactivation in the absence of oxygen was lower than its presence. 4. Preincubation in the presence of ALA or PBG protected the enzymic activity of ALA-D, PBGase and deaminase against URO I-inactivation both under u.v. light and in the dark. 5. Photoinactivating action of URO I would be mediated by reactive oxygen species generated by the excited porphyrin after its absorption of light. Dark inactivation, in aerobiosis, can also be partly mediated by amino acid oxidation, although to a lesser extent than that observed under u.v. light.

Further evidence on the photodynamic and the novel non-photodynamic inactivation of uroporphyrinogen decarboxylase by uroporphyrin I.

The action of uroporphyrin I (URO I) on the activity of red cell uroporphyrinogen decarboxylase (URO-D) in the dark and under UV light was studied. Light-dependent-and light-independent inactivation was observed. Both effects increased at increasing concentrations of URO I, the former reached its maximum at 150 microM of sensitizer. At 100 microM of URO I, both light and dark inactivation were temperature dependent amounting to about 50% at 30-37 degrees C. The velocity of dark inactivation increased with increasing temperature in the range of 0 to 45 degrees C. Photoinactivation can be ascribed to primary oxidation of essential amino acids, very likely histidyl residues, followed by secondary inter or intrapeptide cross-linking. Dark inactivation could be the result of both oxidation and cross-linking (although to a less degree than that produced by light) and also direct inhibition of the enzyme by induced conformational changes at its active site through binding of the porphyrin to the protein. When the action of URO I was tested on partially purified URO-D, the enzyme appeared to be more susceptible to the dark than to the light effect.

Photodynamic and non-photodynamic action of several porphyrins on the activity of some heme-enzymes.

The action of porphyrins, uroporphyrin I and III (URO I and URO III), pentacarboxylic porphyrin I (PENTA I), coproporphyrin I and III (COPRO I and COPRO III), protoporphyrin IX (PROTO IX) and mesoporphyrin (MESO), on the activity of human erythrocytes delta-aminolevulinic acid dehydratase, porphobilinogenase, deaminase and uroporphyrinogen decarboxylase in the dark and under UV light was investigated. Both photoinactivation and light-independent inactivation was found in all four enzymes using URO I as sensitizer. URO III had a similar action as URO I on porphobilinogenase and deaminase and PROTO IX exerted equal effect as URO I on delta-aminolevulinic acid dehydratase and uroporphyrinogen decarboxylase. Photodynamic efficiency of the porphyrins was dependent on their molecular structure. Selective photodecomposition of enzymes by URO I, greater specificity of tumor uptake by URO I and enhanced porphyrin synthesis by tumors from delta-aminolevulic acid, with predominant formation of URO I, underline the possibility of using URO I in detection of malignant cells and photodynamic therapy.

Photodynamic inactivation of red cell uroporphyrinogen decarboxylase by porphyrins.

The effects of light and porphyrins on the activity of red cell uroporphyrinogen decarboxylase were studied. Photoinactivation of uroporphyrinogen decarboxylase was dependent on uroporphyrin concentration, irradiation time and temperature. Using 40 W/m2 of UV light intensity, 40-45% decreased activity was produced with 200 microM uroporphyrin I, at 37 degrees C and after 2 hr of illumination. It has been demonstrated that porphyrins photoinactivate uroporphyrinogen decarboxylase and a mechanism for this action in relation to skin lesions is proposed.

Is hepatoerythropoietic porphyria a homozygous form of porphyria cutanea tarda? Inheritance of uroporphyrinogen decarboxylase deficiency in a Spanish family.

A patient with hepatoerythropoietic porphyria (HEP) is described. He was shown by a family study to be homozygous for a gene that causes greater than 95% suppression of erythrocyte uroporphyrinogen decarboxylase activity.

Studies on in vitro formation of complexes between porphyrins and chloroquine.

Gel filtration and spectrophotometric studies revealed that uroporphyrin, heptacarboxylic-, and pentacarboxylic-porphyrins form in vitro complexes with chloroquine.

Patterns of porphyrin-excretion in female estrogen-induced porphyria cutanea tarda.

It has been suggested that the urinary profile of porphyrins excreted by female patients with estrogen-induced porphyria cutanea tarda is peculiar in that heptacarboxylic porphyrin equals or exceeds uroporphyrin. The chromatographic pattern of urinary porphyrin excretion was studied in nine females with porphyria cutanea tarda precipitated by estrogens, 129 porphyric males, and nine females, whose porphyria was not hormone-induced. Both female porphyric groups showed absolutely the same urinary chromatographic pattern and looked quite similar to the pattern observed in male patients. None of our female porphyric patients, whether treated with estrogens or not, showed percentage values for the heptacarboxylic porphyrin higher or equal to the uroporphyrin values. Our results do not support the hypothesis that the profile of urinary porphyrin excretion found in estrogen-induced porphyria cutanea tarda is atypical.