Abstract
Despite being one of the most studied proteins in biology, the photolysis mechanism of myoglobin heme affected by endogenous substances free amino acids is still in controversy. The transient absorption and kinetic processes of photo-excited myoglobin in three forms and the effects of free excited tryptophan on redox reaction of myoglobin were monitored by laser flash photolysis. With dual energy superposition of direct light irradiation and indirect energy transferred from the free excited tryptophan, the variation value in optical density (ΔOD) of MetMb increased by 66.7%, from 0.9 to 1.5. The ΔOD value of MbO2 in ferrous form increased from 0.9 to 1.25, while the ΔOD value of DeoxyMb increased from 0.75 to 1.2. The decay time of excited DeoxyMb was prolonged obviously with the excited tryptophan, while the decay time of excited MbO2 and MetMb was shortened significantly. The excited tryptophan could promote laser induced reaction processes of myoglobin in different forms by intermolecular energy transfer to one final similar photo reaction state. The possible photo induced reaction mechanisms of DeoxyMb, MbO2, MetMb with and without free tryptophan were also proposed.
Highlights
The results discovered that the rotation of His-64 was identi ed as the characteristic behaviour of a transient species produced by myoglobin-CO photolysis
F43Y Mb mutant with a tryptophan (Trp)–heme cross-link can efficiently catalyse the oxidation of indole to indigo, which proved the signi cant effects of Trp on myoglobin functions.[20]
Hayon et al.,[21] using laser ash photolysis, showed that the photo-excited tryptophan transformed to a single excited tryptophan accompanied by two nonradiative relaxation pathways
Summary
The optical properties of tryptophan (Trp),[21,22] tyrosine (Tyr),[23] phenylalanine (Phe)[24] and cysteine (Cys)[22] are widely applied in the determination of protein spectrum, especially in the region of near ultraviolet. Hayon et al.,[21] using laser ash photolysis, showed that the photo-excited tryptophan transformed to a single excited tryptophan accompanied by two nonradiative relaxation pathways. Electron (eaqÀ) and tryptophan cationic free radicals Trpc+ are generated rstly, and Trpc+ is rapidly converted into Trpc and H+ ((1) and (2)). The triplet formation 3Trp is generated by intersystem crossing from the photo excited state of singlet formation 1Trp* ((3) and (4)). The molecular energies of various excited tryptophan states are
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