Reactivity of Singlet Oxygen Toward Proteins: The Effect of Structure in Basic Pancreatic Trypsin Inhibitor and in Ribonuclease A

The reactions of singlet oxygen, ¹O₂, with large peptides have been described previously. It was found that even in these systems, which in their native form are generally not supposed to possess a stable structure in solution, the polypeptide does impede the access of ¹O₂ to the amino acids that react readily with ¹O₂. Here we describe the ¹0₂ reaction with two proteins of well-defined structure. The quenching of ¹O₂ by bovine pancreatic trypsin inhibitor (BPTI) and by ribonuclease A (RNase A) was compared to that of a solution at the same concentration as those of its constituent amino acids that react readily with ¹O₂. The proteins were studied in their native form, when partly denatured by splitting their S-S bonds and when fully denatured. It was found that while in the native form the quenching rate constant was seven times lower in BPTI (2.2 vs 15.2 times 10⁷WM^-1 s^-1) and three times lower in RNase A (11.0 vs 32 times 10⁷M^-l s^-1) than in a mixture of its constituent amino acid residues, it increased upon denaturation reaching in the fully denatured state the value of the corresponding amino acid mixture. More striking is the effect of the protein structure when comparing the fraction of the encounters between ¹O₂ and protein, which cause damage to the protein, as reflected in the decrease of its biological activity. This decrease is assumed to be due to the chemical (oxidative) reactions of ¹O₂ in the protein. In the exceptionally stable BPTI the fraction of such encounters was 0.05 and in RNase A it was 0.2, whereas for the amino acid tryptophan in solution, 0.7 of the collisions with ¹O₂ led to a chemical reaction.     

REACTIVITY OF SINGLET OXYGEN TOWARD LARGE PEPTIDES

Abstract— The reactions of singlet oxygen, ¹O₂, with amino acids and their derivatives have been studied previously. It was found that only five amino acid residues interact readily with ¹O₂. Here we describe its reactions with the large peptides melittin, neuropeptide Y (NPY) and insulin in their native and in their denatured forms. The singlet oxygen quenching by a polypeptide was compared with that of a solution at the same concentration as those of its constituent amino acids, which are known to react efficiently with ¹O₂. It was found that the quenching rate by such a mixture exceeded that of the polypeptides in their native form. The ratio of the rate constants for NPY to that of the corresponding amino acid mixture in solution was 0.75. For melittin in its monomeric form it was 0.83 and for a tetramer of melittin (at high ionic strength) it was 0.70. For native insulin the ratio of the rate constants was 0.55. For oxidized insulin with its -S-S- bridges opened the figure became 0.80. However, the quenching by all the polypeptides in their fully denatured form (in the presence of 6 M urea) equalled that of the corresponding amino acid mixtures. Although polypeptides are generally supposed not to possess a stable secondary structure in solution the effects are explained by shielding of some of the reactive amino acid residues in the chain by temporary folding or incipient secondary structures of the native polypeptide.
It is shown that the kinetics for a homogeneous solution of quenchers applies also to measurements in a polypeptide solution where the quenchers are localized along the polypeptide backbone and thus form clusters in solution.     

A hybrid asymptotic solution for the scattering by a pair ofparallel perfectly conducting wedges

The overlapping transition regions of the double diffraction by a pair of parallel wedge edges are considered for the hybrid case where the gap between the edges is small compared to the distances from the source and the observation point (plane-wave-far-field limit) and the scatterer as a whole is large (or infinite). A closed-form asymptotic solution for the scattered field continuous at all angles of incidence and scattering is constructed for this case. The peculiar feature of this solution is a hybrid representation of the field singly diffracted by the first wedge: a part of it is described by a nonuniform, geometrical theory of diffraction (GTD) expression, while the other part is described in terms of the uniform theory of diffraction (UTD). The rest of the diffracted ray fields are described by nonuniform expressions, with singularities mutually canceling on summation. This solution is applied to the scattering by a perfectly conducting rectangular cylinder with appropriate geometrical parameters, and agreement with moment method calculation is demonstrated     

Elimination of infinities in equivalent edge currents, Part II: Physical optics components

A solution finite for all directions of illumination and observation is derived for the physical optics (PO) components of equivalent edge currents. The solution is based on the uniform asymptotic theory of endpoint evaluation of integrals. An extension taking into account the variation of the surface metric with the distance from the edge is presented, and a similar extension for including slope diffraction is indicated. The expressions derived complement the results of our previous work on elimination of infinities from the fringe components of equivalent currents.     

A uniform GTD solution for the far-field scattering by polygonal cylinders and strips

The results of our recent asymptotic treatment of the double diffraction by a pair of parallel perfectly conducting wedges are applied to polygonal cylinders and strips. The combination of the appropriate nonuniform expression for the doubly diffracted ray field with the nonuniform geometrical theory of diffraction (GTD) expressions for the singly diffracted fields yields a uniform, closed-form solution for the far scattered field valid throughout the overlapping transition regions. The advantage over the existing uniform GTD solution for a polygonal cylinder consists in the extension from strictly grazing to nearly grazing incidence. For a strip, the present solution improves upon the accuracy of the previous uniform high-frequency solutions.     

Microspheres of Mixed Proteins

This paper describes the synthesis of mixed proteinaceous microspheres (MPMs) by the sonochemical method. The current fundamental research follows the research of Suslick and co‐workers who have developed a method by which high‐intensity ultrasound is used to make aqueous suspensions of proteinaceous microcapsules filled with water‐insoluble liquids. 1 By using high‐intensity ultrasound, we have synthesized microspheres made of a few different proteins. The three proteins used in the current experiments are bovine serum albumin (BSA), green fluorescent protein (GFP), and cyan fluorescent protein–glucose binding protein–yellow fluorescent fused protein (CFP‐GBP‐YFP). The two synthesized microspheres made of mixed proteins are BSA‐GFP and BSA‐(CFP‐GBP‐YFP). This paper presents the characterization of the sonochemically produced microspheres of mixed proteins. It also provides an estimate of the efficiency of the sonochemical process in converting the native proteins to microspheres.     

Evaluating the Influence of Warmup on Singing Voice Quality Using Acoustic Measures

Vocal warmup is generally accepted as vital for singing performance. However, only a limited number of studies have evaluated this effect quantitatively. In this study, we evaluated the effect of vocal warmup on voice production, among young female singers, using a set of acoustic parameters. Warmup reduced frequency-perturbation (p < 0.001) and amplitude-perturbation values (p < 0.05). In addition, warmup increased singer's formant amplitude (p < 0.05) and improved noise-to-harmonic ratio (p < 0.05). Tone-matching accuracy, however, was not affected by warmup. The effect of vocal warmup on frequency-perturbation parameters was more evident among mezzo-soprano singers than it was among soprano singers. It was also more evident in the low pitch-range than in the higher pitch-ranges (p < 0.05). The results of this study provide valid support for the advantageous effect of vocal warmup on voice quality and present acoustic analysis as a valuable and sensitive tool for quantifying this effect.     

An asymptotic solution for the diffraction by a discontinuity in curvature coupled with surface diffraction

An extension is developed for the asymptotic theory of electromagnetic diffraction by a discontinuity in curvature on a smooth convex perfectly-conducting surface. It covers the case where the rays incident on and diffracted from the discontinuity are nearly tangent to the surface or are creeping rays, so that surface diffraction is involved. This extension is restricted to those diffracted rays lying on the same side of the discontinuity as the incident ray; this includes backscatter but excludes forward scattering.     

Fast fabrication of super-hydrophobic surfaces on polypropylene by replication of short-pulse laser structured molds

A new two-step method, facilitating the rapid generation of super-hydrophobic surface structures via parallel laser processing followed by a replica generation by injection molding is reported. A self-made fused silica-based diffractive optical element (DOE) is applied to distribute the laser energy into a 25×25 dot matrix. This DOE is used as a transmission mask for surface ablation of metal molds, applying short-pulse UV laser pulses. In a subsequent process step, replicas of the processed stamp are produced by variothermal injection molding, enabling the mass production of the surface pattern on plastics parts. The resulting topography facilitates a super-hydrophobic behavior of the fabricated components.     

Metal-insulator transition in a system of superconducting vortices caused by a metallic gate

We address a recent experiment in which a strong decrease of the resistance of a superconducting film has been observed when a remote unbiased gate was placed above the film. Here we explain the experimental finding as a suppression of the vortex tunneling due to the orthogonality catastrophe of the electrons inside the gate. We interpret the change in the resistance of the film as a "metal-insulator" transition in the system of vortices induced by the gate.