PORPHYRIN-INDUCED PROTEIN STRUCTURAL ALTERATIONS OF HEME ENZYMES

Some alterations in the protein structure of delta-aminolevulinic acid dehydratase (ALA-D) and porphobilinogen deaminase (PBG-D) induced by uroporphyrin (URO) and prototoporphyrin (PROTO) have been observed pre viously, To obtain further evidence of these phenomena, the absorption and fluorescence spectra of ALA-D and PBG-D and the total protein con tent of sulfhydryl and free amino groups were analyzed after exposure of the enzymes to URO I and PROTO TX, ALA-D and PBG-D were partially p urified from bovine liver and exposed to URO I or PROTO IX, both in th e dark and under UV Light. All experiments were performed in the enzym e solutions after removing the porphyrins. Absorbance spectra changes in the region of 220-300 nm were registered, indicating the interactio n of the porphyrins with the molecular structure of the enzymes, The m ain changes in the fluorescence spectra were observed in the spectral region of 555 nm, and only slight modifications in the spectral region of 340-360 nm; moreover, alterations were stronger upon UV irradiatio n and in the presence of URO I when compared with darkness and PROTO I X, Variations in total SH groups would suggest the formation of disulf ur bridges induced by URO I and the rupture of some S-S groups induced by PROTO IX. The effect of porphyrins on free amino groups mould refl ect a combination of cross-linking and fragmentation of proteins, Stru ctural changes mere observed when the enzymes mere exposed to the porp hyrin both in the dark or under UV light; however, they were stronger in the latter condition, These results suggest that porphyrins per. se could act directly on the protein structure and that this action moul d be enhanced upon UV irradiation. (C) 1997 Elsevier Science Ltd.