title: A study of the properties of two porphyringlobin species formed in the reaction of protoporphyrin IX with human globin.
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.
mesh_terms: D001665:Binding Sites; D002852:Chromatography, Ion Exchange; D005914:Globins; D006454:Hemoglobins; D006801:Humans; D007700:Kinetics; D008027:Light; D046911:Macromolecular Substances; D008433:Mathematics; D010108:Oxyhemoglobins; D010777:Photochemistry; D011166:Porphyrins; D011485:Protein Binding; D011725:Pyridines; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013439:Sulfhydryl Reagents; D013997:Time Factors; D014461:Ultracentrifugation
chemical_list: D006454:Hemoglobins; D046911:Macromolecular Substances; D010108:Oxyhemoglobins; D011166:Porphyrins; D011725:Pyridines; D013439:Sulfhydryl Reagents; D005914:Globins