Protein damage and degradation by oxygen radicals. II. Modification of amino acids.

— The photophysics and photochemistry of tryptophan and its simple derivatives is comprehensively reviewed with special emphasis on excitation by near-UV radiation. Topics explicitly discussed include the origins of large Stokes shifts in the fluorescence spectra, photoionization, the puzzle of multiple tryptophan fluorescence decay time, photochemical reactions in the presence and absence of oxygen, and the possible mechanisms of these reactions. A separate section reviews the photosensitizing properties of N-formylkynurenine, an important photooxidation product of tryptophan.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1751-1097.1984.tb03890.x

The photophysics and photochemistry of the near-uv absorbing amino acids–ii. tyrosine and its simple derivatives

Nanoparticles used for biological and biomedical applications encounter a host of extracellular proteins. These proteins rapidly adsorb onto the nanoparticle surface, creating a protein corona. Poly(ethylene glycol) can reduce, but not eliminate, the nonspecific adsorption of proteins. As a result, the adsorbed proteins, rather than the nanoparticle itself, determine the cellular receptors used for binding, the internalization mechanism, the intracellular transport pathway, and the subsequent immune response. Using fluorescence microscopy and flow cytometry, we first characterize a set of polystyrene nanoparticles in which the same adsorbed protein, bovine serum albumin, leads to binding to two different cell surface receptors: native albumin receptors and scavenger receptors. Using a combination of circular dichroism spectroscopy, isothermal titration calorimetry, and fluorescence spectroscopy, we demonstrate that the secondary structure of the adsorbed bovine serum albumin protein controls the cellular ...

https://pubs.acs.org/doi/pdf/10.1021/jp502624n

Secondary structure of corona proteins determines the cell surface receptors used by nanoparticles.

Perfluorochemicals are globally pervasive contaminants that are persistent, bioaccumulative, and toxic Perfluorocarboxylic acids (PFCAs) with 8−13 carbons accumulate in the liver and blood of aquatic organisms; PFCA−protein interactions may explain this accumulation pattern Here, the interactions between PFCAs with 8−11 carbons and serum albumin are examined using three experimental approaches: surface tension titrations, 19F NMR spectroscopy, and fluorescence spectroscopy Surface tension titrations indicate complex formation at high (mM) PFCA concentrations Secondary association constants ranging from 102 to 104 M−1 were determined from 19F NMR titrations at high PFCA:albumin mole ratios Fluorescence measurements indicate that PFCA−albumin interactions alter the protein conformation at low PFCA:albumin mole ratios (up to 5:1) and suggest two binding classes with association constants around 105 and 102 M−1 While 19F NMR and fluorescence provide both qualitative and quantitative information about PF

Binding of Perfluorocarboxylates to Serum Albumin: A Comparison of Analytical Methods

A recently discovered photodecarboxylase from Chlorella variabilis NC64A ( CvFAP) bears the promise for the efficient and selective synthesis of hydrocarbons from carboxylic acids. CvFAP, however, exhibits a clear preference for long-chain fatty acids thereby limiting its broad applicability. In this contribution, we demonstrate that the decoy molecule approach enables conversion of a broad range of carboxylic acids by filling up the vacant substrate access channel of the photodecarboxylase. These results not only demonstrate a practical application of a unique, photoactivated enzyme but also pave the way to selective production of short-chain alkanes from waste carboxylic acids under mild reaction conditions.

Hydrocarbon Synthesis via Photoenzymatic Decarboxylation of Carboxylic Acids.

— The quantum yields and lifetimes of the fluorescence of tyrosine and tryptophan were determined in D2O-H2O and glycerol-H2O solvent mixtures of varying composition from 10 vol.% to 100% H2O at 15°C. Forboth amino acids the ratio of the quantum yields in D2O and H2O (i.e., qD/qH) was smaller than the ratio of the corresponding lifetimes (D/H). For tyrosine the ratio of the quantum yields in glycerol and H2O (qG/qH) was also smaller than the corresponding G/H ratio, but for tryptophan qG/gHG/H. The proximity of the q vs. plots for tyrosine in the two solvent mixtures indicates that at 15°C neither D2O nor glycerol, in the pure state or when diluted with H2O, quench tyrosine significantly. However, H2O quenches tyrosine by a dynamic process, which increases both the radiative and the nonradiative rate constant. The quenching action is attributed to a tyrosine-H2O exciplex, whose formation is independent of bulk viscosity and dielectric constant. Unlike tyrosine, tryptophan is quenched weakly by D2O by a static process at 15°C (i.e., involving no change in), but H2O quenches tryptophan much more efficiently by a dynamic process, which involves the nonradiative rate constant, but not the radiative constant. These results are explained on the basis of electrostatic complexation of the ammonium group to the carbon atom adjacent to the ring nitrogen with a lifetime which is longer thanin D2O but shorter thanin H2O, with solvent reorientation possibly also being an important factor in the quenching. This explanation is consistent with the fact that concentrated (8 M) urea increases q andof aqueous tryptophan ˜ 15–20%, while guanidine hydrochloride (6.4 M) has the opposite effect, i.e., it decreases q and t of tryptophan ˜ 15–20%, and with the fact that neither 8 M urea nor 6.4 M guanidine hydrochloride affects any fluorescence parameter of tyrosine at all.

The quenching of tyrosine and tryptophan fluorescence by h2o and d2o

The fluorescence parameters, lifetime, relative quantum yield, maximum and mean wavelength, half-width, and polarization, of bovine serum albumin (BSA) were measured at 15°C in aqueous solutions containing varying concentrations of different chemical perturbants, glycerol, Cu2+ ions, guanidine hydrochloride, and urea. By considering a quenching mechanism as being either dynamic or static, depending upon whether the quenching is or is not accompanied by a change in the fluorescence lifetime, we were able to correlate the changes produced in the various fluorescence parameters by the different chemical perturbants with changes in macromolecular structure as the concentration of perturbant was gradually increased. The addition of glycerol and of Cu2+ ions indicated that in aqueous BSA both tryptophan residues are below the surface of the macromolecule, out of contact with solvent water, and, as a consequence, they are statically quenched. “Ultra-Pure” guanidine hydrochloride at 2.4 M or more caused a drastic conformation change, which resulted in the emergence of a visible tyrosine peak at 304 nm in the BSA fluorescence spectrum when either 260- or 270-nm excitation was employed. With the same excitation, the enhancement of BSA tyrosine fluorescence by 6–8 M ultra-pure urea produced only a shoulder near 304 nm in the BSA fluorescence spectrum. We have introduced the use of a new relative quantum yield for protein fluorescence, q′, referenced to the quantum yield of unquenched free tryptophan, which eliminates the quenching action of water from the reference.

Static and dynamic quenching of protein fluorescence. I. Bovine serum albumin.

The fluorescence parameters—lifetime, relative quantum yield, wavelength of maximum fluorescence intensity, half-width, and polarization—of 0.01% lysozyme were measured at 15°C in aqueous solution, in glycerol–water mixtures (0–90% v/v glycerol), in aqueous urea (0–8M) solutions, and in aqueous guanidine hydrochloride (0–6.4M) solutions. The changes in the static and dynamic quenching of lysozyme fluorescence, monitored by the quantum yield and lifetime measurements, were correlated with the other fluorescence parameters and compared with our earlier results with bovine serum albumin.



The results were interpreted in terms of induced conformational changes. The various perturbants altered the fluorescence parameters of lysozyme and bovine serum albumin very differently. The differences were shown to be entirely consistent with our earlier conclusion that bovine serum albumin fluorophores are nonsurface residues and with the conclusion of others that lysozyme fluorophores are surface residues. Unlike their effects on bovine serum albumin, urea and guanidine hydrochloride affect lysozyme structure quite differently, both in nature and degree. We have suggested that the affect of urea on lysozyme fluorescence is an indirect result of reduction in the size of the cleft brought about by the structure-breaking action of urea on water in the cleft. 4M Urea is sufficient for this reaction.



Large decreases in the polarization of the fluorescence of lysozyme in the 0.8–1.6M and 3.2–4.8M guanidine hydrochloride ranges demonstrated two guanidine hydrochloride-induced conformation changes. A red shift of the fluorescence maximum to 354 nm indicated that the second transition completely exposes all fluorescing tryptophan residues of lysozyme to mobile solvent water. However, even 6.4M guanidine hydrochloride did not completely unravel the lysozyme molecule at 15°C, as evidenced by its failure to cause any of the tyrosine residues to become fluorescent.

Static and dynamic quenching of protein fluorescence. II. Lysozyme

We present the design and fabrication of a diffractive element that increases the effective numerical aperture of a scanned retinal display. This enables a large exit pupil to be achieved in helmet-mounted applications.

Diffractive optical elements for numerical aperture expansion in retinal scanning displays

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The quenching of tyrosine and tryptophan fluorescence by h2o and d2o

Static and dynamic quenching of protein fluorescence. I. Bovine serum albumin.

Static and dynamic quenching of protein fluorescence. II. Lysozyme

Diffractive optical elements for numerical aperture expansion in retinal scanning displays