Photodynamic and light independent action of 8 to 2 carboxylic free porphyrins on some haem-enzymes

Backgrounds and aims: skin lesions in cutaneous porphyrias appear to be det ermined by the structural properties of the porphyrins accumulated. To bett er understand the relationship between the structure and physicochemical pr operties of porphyrins and their specific effect on protein configuration, the action of a whole range of 8 to 2 carboxylic porphyrins has been studie d. Materials and methods: delta -aminolevulinic acid dehydratase (ALA-D) an d porphobilinogen deaminase (PBG-D) partially purified from bovine liver, w ere exposed to 10 muM uroporphyrin (Uro), phyriaporphyrin (Phyria), hexapor phyrin (Hexa), pentaporphyrin (Penta), coproporphyrin (Copro) or protoporph yrin (Proto), either in the dark or under UV light. All experiments were pe rformed in the enzyme solutions after removing the porphyrins. Results: und er both illuminating conditions, all porphyrins inactivated the enzymes (20 -70% under control values), indicating photodynamic action mediated by oxid ative reactions and conformational changes due to direct binding of porphyr ins to the protein. Total thiol content in ALA-D was not significantly chan ged by most porphyrins under UV light, while all porphyrins increase total sulfhydryl groups in PBG-D (23-52% over the control values) indicating chan ges in the redox status of SH residues. Free amino groups were reduced by a ll porphyrins in ALA-D (23-56% under controls), instead they were enhanced in PBG-D (23-51% over controls), suggesting protein fragmentation. The form ation of molecular aggregates would be the consequence of cross-links betwe en oxidation products. while fragmentation can be attributed to either rupt ure of disulphur bridges and/or enhancement of free amino groups on the pro tein enzyme. Conclusions: the effect of the porphyrins on enzyme activity, total SH groups and free amino groups content, was different for ALA-D and PBG-D, even under the same illuminating conditions. On the basis of these r esults, no correlation between enzyme alterations and the physicochemical p roperties of porphyrins could be established. (C) 2001 Elsevier Science Ltd . All rights reserved.