Reaction of Singlet Oxygen with Tryptophan in Proteins: A Pronounced Effect of the Local Environment on the Reaction Rate

Abstract

Singlet molecular oxygen, O(2)(a(1)Δ(g)), can influence many processes pertinent to the function of biological systems, including events that result in cell death. Many of these processes involve a reaction between singlet oxygen and a given amino acid in a protein. As a result, the behavior of that protein can change, either because of a structural alteration and/or a direct modification of an active site. Surprisingly, however, little is known about rate constants for reactions between singlet oxygen and amino acids when the latter are in a protein. In this report, we demonstrate using five separate proteins, each containing only a single tryptophan residue, that the rate constant for singlet oxygen reaction with tryptophan depends significantly on the position of this amino acid in the protein. Most importantly, the reaction rate constant depends not only on the accessibility of the tryptophan residue to oxygen, but also on factors that characterize the local molecular environment of the tryptophan in the protein. The fact that the local protein environment can either appreciably inhibit or accelerate the reaction of singlet oxygen with a given amino acid can have significant ramifications for singlet-oxygen-mediated events that perturb cell function.

Subtle Differences in Virus Composition Affect Disinfection Kinetics and Mechanisms

“…We note here that the local environment and accessibility to a specific site have been reported as being crucial elements in accounting for protein reactivity toward 1 O 2 (39). Free chlorine.…”

Scope and limitations of the TEMPO/EPR method for singlet oxygen detection: the misleading role of electron transfer

“…Its reactions include oxidation of lipids [1][2], proteins [3][4][5] and nucleic acids [6][7][8], that may trigger a biological damage. This reaction cascade can lead to undesired adverse effects, like drug-induced phototoxicity [9][10], but can also be exploited to produce beneficial effects as in photodynamic therapy [11][12].…”

Photochemistry and Spectroscopy of Singlet Oxygen in Solvents. Recent Advances which Support the Old Theory

“…The realm of chemical phenomena in which the singlet g a ∆ 1 oxygen participates is now great and wonderful [39,40,57] with most applications in medicine [58][59][60][61][62]. Thus, it is important to know all physicochemical factors determining the O 2 ( g a∆ 1 ) lifetime in various environments, especially in biological solvents [40,59].…”

“…Thus, it is important to know all physicochemical factors determining the O 2 ( g a∆ 1 ) lifetime in various environments, especially in biological solvents [40,59]. Extensive experimental studies during last five decades [1][2][3] provide huge information and its systematization attempts occur often in various reviews [1,19,27,32,40,[61][62][63][64].…”