title: Different characteristics of ferrochelatase in cultured fibroblasts of erythropoietic protoporphyria patients and normal controls.
abstract: Ferrochelatase activity was measured in crude extracts of fibroblasts, obtained from erythropoietic protoporphyria patients and healthy controls. The enzyme activity in erythropoietic protoporphyria fibroblasts was about 50% lower, compared to the controls. The sulfhydryl-oxidising reagent diamide inhibited the normal enzyme by about 50%, whereas ferrochelatase from erythropoietic protoporphyria fibroblasts was completely insensitive to the reagent. Pb2+ inhibits ferrochelatase activity by reacting with essential sulfhydryl groups. Low concentrations of Pb2+ inhibited the normal enzyme by 56%, but the mutant enzyme by only 8%. The photodynamic activity of bound mesoporphyrin substrate caused a biphasic inactivation of the normal enzyme. During the first 5 min of illumination a fast decrease of enzyme activity occurred to about 60% of the initial value. Experimental evidence indicates that this first phase of inactivation is caused by photooxidation of sulfhydryl groups. During further illumination inactivation continued at a much slower rate. With ferrochelatase from erythropoietic protoporphyria fibroblasts only the second, slow phase of photodynamic inactivation was observed. These observations suggest a mutation of ferrochelatase in erythropoietic protoporphyria, affecting the reactivity of sulfhydryl groups, involved in the catalytic activity of the enzyme.
authors.affiliation: Sylvius Laboratories, Department of Medical Biochemistry, Leiden, The Netherlands.
authors.forename: C
authors.initials: C
authors.lastname: Blom
authors.forename: E C
authors.initials: EC
authors.lastname: Klasen
authors.forename: J
authors.initials: J
authors.lastname: Van Steveninck
mesh_terms: D004920:Erythropoiesis; D005294:Ferrochelatase / Q000378:metabolism*; D005347:Fibroblasts / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D008190:Lyases / Q000378:metabolism*; D011164:Porphyrias / Q000201:enzymology*; D012016:Reference Values; D012867:Skin / Q000201:enzymology*
chemical_list: D008190:Lyases; D005294:Ferrochelatase