Proton-Coupled Electron Transfer and Redox-Active Tyrosines: Structure and Function of the Tyrosyl Radicals in Ribonucleotide Reductase and Photosystem II

Barry, Bridgette A.; Chen, Jun; Keough, James M.; Jenson, David L.; Offenbacher, Adam R.; Pagba, Cynthia V.

doi:10.1021/jz2014117

Cited by 43 publications

(77 citation statements)

References 107 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Increasing hydration decreases the activation energy, and moderate hydration levels, confer semiconductor-like properties on the collagen, with water possibly acting as an impurity [15]. Although the exact mechanism of tyrosyl formation is unclear, we can speculate that moderate hydration lowers the activation energy sufficiently to allow tyrosine oxidation via electron transfer (ET), proton transfer (PT), or proton-coupled electron transfer (PCET) (for review of PCET, see [16]). In buffered solution, tyrosyl formation could also have been facilitated by the presence of phosphate buffer [17].…”

Section: Discussionmentioning

confidence: 99%

Thermal and Photochemical Effects on the Fluorescence Properties of Type I Calf Skin Collagen Solutions at Physiological pH

Menter¹,

Freeman²,

Edukuye³

2015

OJPC

View full text Add to dashboard Cite

Mammalian collagens exhibit weak intrinsic UV fluorescence that depends on the age and previous history of the sample. Post-translational modifications result in additional fluorescent products (e.g. DOPA, dityrosine, and advanced glycation end products (AGE)). UV radiation can cause longer wavelength fluorescent oxidative bands. These alterations can assess the extent of photolysis. We describe the ground-and excited-state oxidative transformations of newly-purchased type I calf skin collagens (samples #092014 and #072012) and a 7-year-old sample (#072005). We compare the effects of UV radiation (mainly 254 nm) and age on the photochemical reaction kinetics and fluorescence spectral distribution of type I calf skin collagen at pH 7.4. The fluorescence spectra of samples #072012 and #092014 were similar but not identical to pure tyrosine, whereas #072005 indicated significant "dark" oxidation at the expense of tyrosine. Fading of oxidized product(s) at 270/360 nm is second-order. Build-up of 325/400 nm (dityrosine) fluorescence is linear with time. Rate parameters r2 and r 1 were respectively proportional to second order disappearance of ground state oxidation products and the quasi-first-order photochemical formation of dityrosine. There is a reciprocal relationship between the rates of decrease in the 270/360 nm fluorescence and concomitant increase in 325/400 nm fluorescence. Their relative rates depend on the age of the collagen sample. There is a reciprocal relationship between r 1 and r 2 . This relationship results because both ground state autoxidation and excited state photo-dimerization proceed via a common tyrosyl radical intermediate. Water of hydration appears to play a role in generating tyrosyl radical.

show abstract

Section: Discussionmentioning

confidence: 99%

Thermal and Photochemical Effects on the Fluorescence Properties of Type I Calf Skin Collagen Solutions at Physiological pH

Menter¹,

Freeman²,

Edukuye³

2015

OJPC

View full text Add to dashboard Cite

show abstract

“…The PSII membranes (referred to as BBY) were isolated from fresh spinach leaves as described previously [22,23]. Their final Chl concentrations were in the range 2.2-2.7 mg Chl mL −1 , and oxygen evolution rates were over 800 μmol O 2 (mg Chl) − 1 h −1 [24].…”

Section: Psii Samplesmentioning

confidence: 99%

Directly probing redox-linked quinones in photosystem II membrane fragments via UV resonance Raman scattering

Chen

Yao

Pagba

et al. 2015

Biochimica et Biophysica Acta (BBA) - Bioenergetics

Self Cite

View full text Add to dashboard Cite

In photosynthesis, photosystem II (PSII) harvests sunlight with bound pigments to oxidize water and reduce quinone to quinol, which serves as electron and proton mediators for solar-to-chemical energy conversion. At least two types of quinone cofactors in PSII are redox-linked: QA, and QB. Here, we for the first time apply 257-nm ultraviolet resonance Raman (UVRR) spectroscopy to acquire the molecular vibrations of plastoquinone (PQ) in PSII membranes. Owing to the resonance enhancement effect, the vibrational signal of PQ in PSII membranes is prominent. A strong band at 1661 cm(-1) is assigned to ring CC/CO symmetric stretch mode (ν8a mode) of PQ, and a weak band at 469 cm(-1) to ring stretch mode. By using a pump-probe difference UVRR method and a sample jet technique, the signals of QA and QB can be distinguished. A frequency difference of 1.4 cm(-1) in ν8a vibrational mode between QA and QB is observed, corresponding to ~86 mV redox potential difference imposed by their protein environment. In addition, there are other PQs in the PSII membranes. A negligible anharmonicity effect on their combination band at 2130 cm(-1) suggests that the 'other PQs' are situated in a hydrophobic environment. The detection of the 'other PQs' might be consistent with the view that another functional PQ cofactor (not QA or QB) exists in PSII. This UVRR approach will be useful to the study of quinone molecules in photosynthesis or other biological systems.

show abstract

“…The pK a,sol of an isolated Tyrosine is 10.9 [214], while the pK a,sol of the oxidized Y · H + is −2 [215], so a proton must be lost as the Tyr is oxidized. However, Y z is only transiently deprotonated, as it must rebind a proton to oxidize the OEC [216].…”

Section: Mechanism Of Proton Binding and Release That Generate Thementioning

confidence: 99%

“…The chemistry of redox active amino acids such as Tyr and Trp are well characterized [211, 214, 321, 322]. For Tyr the pK a,sol of the ground state is 10.9 [323].…”

Section: Mechanism Of Proton Binding and Release That Generate Thementioning

confidence: 99%

Molecular mechanisms for generating transmembrane proton gradients

Gunner

Amin

Zhu

et al. 2013

Biochimica et Biophysica Acta (BBA) - Bioenergetics

View full text Add to dashboard Cite

Membrane proteins use the energy of light or high energy substrates to build a transmembrane proton gradient through a series of reactions leading to proton release into the lower pH compartment (P-side) and proton uptake from the higher pH compartment (N-side). This review considers how the proton affinity of the substrates, cofactors and amino acids are modified in four proteins to drive proton transfers. Bacterial reaction centers (RCs) and photosystem II (PSII) carry out redox chemistry with the species to be oxidized on the P-side while reduction occurs on the N-side of the membrane. Terminal redox cofactors are used which have pKas that are strongly dependent on their redox state, so that protons are lost on oxidation and gained on reduction. Bacteriorhodopsin is a true proton pump. Light activation triggers trans to cis isomerization of a bound retinal. Strong electrostatic interactions within clusters of amino acids are modified by the conformational changes initiated by retinal motion leading to changes in proton affinity, driving transmembrane proton transfer. Cytochrome c oxidase (CcO) catalyzes the reduction of O2 to water. The protons needed for chemistry are bound from the N-side. The reduction chemistry also drives proton pumping from N- to P-side. Overall, in CcO the uptake of 4 electrons to reduce O2 transports 8 charges across the membrane, with each reduction fully coupled to removal of two protons from the N-side, the delivery of one for chemistry and transport of the other to the P-side.

show abstract

Proton-Coupled Electron Transfer and Redox-Active Tyrosines: Structure and Function of the Tyrosyl Radicals in Ribonucleotide Reductase and Photosystem II

Cited by 43 publications

References 107 publications

Thermal and Photochemical Effects on the Fluorescence Properties of Type I Calf Skin Collagen Solutions at Physiological pH

Thermal and Photochemical Effects on the Fluorescence Properties of Type I Calf Skin Collagen Solutions at Physiological pH

Directly probing redox-linked quinones in photosystem II membrane fragments via UV resonance Raman scattering

Molecular mechanisms for generating transmembrane proton gradients

Contact Info

Product

Resources

About