A study of the reaction of protoporphyrin IX with human globin

Abstract

The present paper reports an investigation of the reaction of protoporphyrin IX with globin prepared from the HbA₀ component of human blood. The porphyringlobin produced is always heterogeneous; however, when globin is used immediately after preparation, its affinity for porphyrin is higher and the product less heterogeneous than when the globin has been frozen or freeze-dried. The affinity of globin for haemin is less affected by its history. With freshly prepared globin, reconstitution at room temperature provides a different distribution of porphyringlobin species than reconstitution at 4°C. Further changes in the species distribution of cold-reconstituted samples may be observed by gel electrophoresis when the samples are aged for 24h at room temperature. Chromatographic separation of such porphyringlobin samples on CM-Sephadex generally revealed five species with two in predominating amounts. It was consistently observed that over a period of 18 days, the faster moving of the two main components decreased in amount whereas the slower-moving component correspondingly increased. However, when the main components are separated, they remain homogeneous over the same length of time. The effect of light on porphyringlobin was also investigated. It was shown that porphyringlobin is photo-oxidized: as a result the porphyrin is destroyed together with most of the histidine, methionine and all of the tryptophan residues of the protein.