A study of the properties of two porphyringlobin species formed in the reaction of protoporphyrin IX with human globin |
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Authors: | Stanley Ainsworth and Amyra Treffry |
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Institution: | Department of Biochemistry, University of Sheffield, Sheffield S10 2TN, U.K. |
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Abstract: | Globin was prepared from the main (A(0)) component of human haemoglobin and reacted with protoporphyrin IX; the product, when subjected to chromatography on CM-Sephadex, separated into fast- and slow-moving species. These were isolated for examination. The dissociation constant for the tetramer-dimer equilibrium of fast-moving porphyringlobin was determined at 2.8x10(-6)m; this is to be compared with values of 2.2x10(-6)m and 8x10(-8)m determined for oxyhaemoglobin and the slow-moving porphyringlobin respectively. It was also shown that the thiol groups of fast-moving porphyringlobin react with 4,4'dithiodipyridine at an identical rate with those of oxyhaemoglobin; in comparison, the rates of reaction of deoxyhaemoglobin and porphyringlobin are much slower but are again identical with one another. The quenching of porphyringlobin fluorescence by I(-) ions was also studied. The quenching could not be represented by a simple Stern-Volmer relationship (whereas that of porphyrin-apomyoglobin is), but was represented by a model in which the fluorescence of fast-moving porphyringlobin was more accessible to the quencher than that of the slow-moving component. Similarly, fast-moving porphyringlobin was photodecomposed more rapidly by oxygen than the slow-moving species. |
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