Biochemical reactions involving electron transfer between substrates or enzyme cofactors are both common and physiologically important; they have been studied by means of a variety of techniques. In this paper we review the application of photochemical methods to the study of intramolecular electron transfer in hemoproteins, thus selecting a small, well-defined sector of this otherwise enormous field. Photoexcitation of the heme populates short-lived excited states which decay by thermal conversion and do not usually transfer electrons, even when a suitable electron acceptor is readily available, e.g., in the form of a second oxidized heme group in the same protein; because of this, the experimental setup demands some manipulation of the hemoprotein. In this paper we review three approaches that have been studied in detail: (i) the covalent conjugation to the protein moiety of an organic ruthenium complex, which serves as the photoexcitable electron donor tin this case the heme acts as the electron acceptor); (ii) the replacement of the heme group with a phosphorescent metal-substituted porphyrin, which on photoexcitation populates long-lived excited states, capable of acting as electron donors (clearly the protein must contain some other cofactor acting as the electron acceptor, most often a second heme group in the oxidized state); (iii) the combination of the reduced heme with CO (the photochemical breakdown of the iron-CO bond yields transiently the ground-state reduced heme which is able to transfer one electron (or a fraction of it) to an oxidized electron acceptor in the protein; this method uses a "mixed-valence hybrid" state of the redox active hemoprotein and has the great advantage of populating on photoexcitation an electron donor at physiological redox potential). (C) 2001 Academic Press.
Photochemically induced electron transfer / Bellelli, Andrea; Brunori, Maurizio; P., Brzezinski; M. T., Wilson. - In: METHODS. - ISSN 1046-2023. - STAMPA. - 24:2(2001), pp. 139-152. [10.1006/meth.2001.1175]
Photochemically induced electron transfer
BELLELLI, Andrea;BRUNORI, Maurizio;
2001
Abstract
Biochemical reactions involving electron transfer between substrates or enzyme cofactors are both common and physiologically important; they have been studied by means of a variety of techniques. In this paper we review the application of photochemical methods to the study of intramolecular electron transfer in hemoproteins, thus selecting a small, well-defined sector of this otherwise enormous field. Photoexcitation of the heme populates short-lived excited states which decay by thermal conversion and do not usually transfer electrons, even when a suitable electron acceptor is readily available, e.g., in the form of a second oxidized heme group in the same protein; because of this, the experimental setup demands some manipulation of the hemoprotein. In this paper we review three approaches that have been studied in detail: (i) the covalent conjugation to the protein moiety of an organic ruthenium complex, which serves as the photoexcitable electron donor tin this case the heme acts as the electron acceptor); (ii) the replacement of the heme group with a phosphorescent metal-substituted porphyrin, which on photoexcitation populates long-lived excited states, capable of acting as electron donors (clearly the protein must contain some other cofactor acting as the electron acceptor, most often a second heme group in the oxidized state); (iii) the combination of the reduced heme with CO (the photochemical breakdown of the iron-CO bond yields transiently the ground-state reduced heme which is able to transfer one electron (or a fraction of it) to an oxidized electron acceptor in the protein; this method uses a "mixed-valence hybrid" state of the redox active hemoprotein and has the great advantage of populating on photoexcitation an electron donor at physiological redox potential). (C) 2001 Academic Press.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.