The protective function of hydrogen sulfide for lysozyme against riboflavin-sensitized photo-oxidation

Endogenous reactive oxygen species (ROS)-driven protein oxidation regulates emulsifying and foaming properties of liquid egg white

Highly oxidative reactive oxygen species (ROS) attack protein structure and regulate its functional properties. The molecular structures and functional characteristics of egg white (EW) protein (EWP) during 28 d of aerobic or anaerobic storage were explored to investigate the "self-driven" oxidation mechanism of liquid EW mediated by endogenous ROS signaling. Results revealed a significant increase in turbidity during the storage process, accompanied by protein crosslinking aggregation. The ROS yield initially increased and then decreased, leading to a substantial increase in carbonyl groups and tyrosine content. The free sulfhydryl groups and molecular flexibility in EWP exhibited synchronicity with ROS production, reflecting the self-repairing ability of cysteine residues in EWP. Fourier-transform infrared spectroscopy indicated stable crosslinking between EWP molecules in the early oxidation stage. However, continuous ROS attacks accelerated EWP degradation. Compared with the control group, the aerobic-stimulated EWP showed a significant decrease in foaming capacity from 30.5 % to 9.6 %, whereas the anaerobic-stimulated EWP maintained normal levels. The emulsification performance exhibited an increasing-then-decreasing trend. In conclusion, ROS acted as the predominant factor causing deterioration of liquid EW, triggering moderate oxidation that enhanced the superior foaming and emulsifying properties of EWP, and excessive oxidation diminished the functional characteristics by affecting the molecular structure.

An innovative study on the "on-off-on" detection of sulfur ions based on a TSPP-riboflavin fluorescent probe

In this paper, 5,10,15,20-(4-sulphonatophenyl) porphyrin (TSPP) was synthesized by a facile route and used as a fluorescent probe to construct a sensor system based on the high water solubility and high quantum yield. It was found that when riboflavin (RF) was introduced into the TSPP solution, the fluorescence intensity of TSPP decreased for the peaks at 645 nm and 700 nm based on the principle of the electrostatic attractions and hydrophobic interactions between TSPP and riboflavin. When the fluorescence emission peak of riboflavin appeared at 550 nm, the fluorescence sensor system changed from the "on" state to the "off" state. When sulfur ions (S2-) were further introduced into the TSPP-riboflavin system, the fluorescence intensity of riboflavin was further decreased based on the specific reaction between S2- and riboflavin. However, the fluorescence signal of TSPP was restored and the fluorescence sensing system changed from the "off" state to the "on" state. Therefore, TSPP was used as a fluorescent probe to construct an "on-off-on" fluorescent sensing system, the linear range of S2- detected by this system is 5.0 × 10-9 to 3.6 × 10-5 M, and the detection limit (LOD) is 1.1 × 10-9 M. The sensing system has higher accuracy and sensitivity, and it can be successfully used in the sensing of S2- in real samples.

Sensitized photo-oxidation of plant cytokinin-specific binding protein - Does the environment of the thioether group influence the oxidation reaction? From primary intermediates to stable products

The reactions of protein oxidation play a significant role in many biological processes, especially in diseases development. Therefore, it is important to understand, how the protein molecule behaves in the presence of oxidants. In the present work, photo-oxidation of phytohormone-binding plant protein (VrPhBP) was investigated using light and 3-carboxybenzophenone (3CB) as a sensitizer (one electron oxidant). The protein interacts with the sensitizer in the ground state forming a weak binding complex leading to the presence of bound and free 3CB in solution. The early events and transient species (such as radicals and radical ions) formed during irradiation were characterised by transient spectroscopy showing the formation of the sulphur radical cation Met>S^●+ (stabilized by (S∴N)⁺)and the tyrosyl radical TyrO^● on VrPhBP. Thus the 3CB excited triplet state was quenched by the Met and Tyr residues and mostly by Met (based on the deconvoluted transient absorption spectra).The presence of a Tyr side chain in the vicinity of a Met residue results in intramolecular electron transfer from Tyr to the Met>S^●+ radical cation, leading to regeneration of the thioether side chain and formation of TyrO^●. The presence of other side chains close to Met, such as Arg or Lys can induce the stabilization of Met>S^●+ via the formation of two-centered three-electron bonded species (S∴N)⁺. The transient species were additionally confirmed by stable product analysis. Based on SDS-PAGE, chromatography and mass spectrometry, the formation of methionine sulphoxide and Met-3CB adduct was identified together with di-Tyr cross links. On the basis of the experimental results the overall mechanism of VrPhBP photo-oxidation, from its early events to the formation of stable products, is described. In addition, a good correlation between the mechanisms of photooxidation of model compounds such as Met derivatives and peptides and those for real biological systems is emphasized.

Chemical foundations of hydrogen sulfide biology

Following nitric oxide (nitrogen monoxide) and carbon monoxide, hydrogen sulfide (or its newer systematic name sulfane, H2S) became the third small molecule that can be both toxic and beneficial depending on the concentration. In spite of its impressive therapeutic potential, the underlying mechanisms for its beneficial effects remain unclear. Any novel mechanism has to obey fundamental chemical principles. H2S chemistry was studied long before its biological relevance was discovered, however, with a few exceptions, these past works have received relatively little attention in the path of exploring the mechanistic conundrum of H2S biological functions. This review calls attention to the basic physical and chemical properties of H2S, focuses on the chemistry between H2S and its three potential biological targets: oxidants, metals and thiol derivatives, discusses the applications of these basics into H2S biology and methodology, and introduces the standard terminology to this youthful field.

Hydrogen sulfide in biochemistry and medicine

SIGNIFICANCE

An abundance of experimental evidence suggests that hydrogen sulfide (H(2)S) plays a prominent role in physiology and pathophysiology. Many targets exist for H(2)S therapy. The molecular targets of H(2)S include proteins, enzymes, transcription factors, and membrane ion channels.

RECENT ADVANCES

Novel H(2)S precursors are being synthesized and discovered that are capable of releasing H(2)S in a slow and sustained manner. This presents a novel and advantageous approach to H(2)S therapy for treatment of chronic conditions associated with a decline in endogenous H(2)S, such as diabetes and cardiovascular disease.

CRITICAL ISSUES

While H(2)S is cytoprotective at physiological concentrations, it is not universally cytoprotective, as it appears to have pro-apoptotic actions in cancer cells and is well known to be toxic at supraphysiological concentrations. Many of the pleiotropic effects of H(2)S on health are associated with the inhibition of inflammation and upregulation of prosurvival pathways. The powerful anti-inflammatory, cytoprotective, immunomodulating, and trophic effects of H(2)S on the vast majority of normal cells seem to be mediated mainly by its actions as an extremely versatile direct and indirect antioxidant and free radical scavenger. While the overall effects of H(2)S on transformed (i.e., malignant) cells can be characterized as pro-oxidant and pro-apoptotic, they contrast sharply with the cytoprotective effects on most normal cells.

FUTURE DIRECTIONS

H(2)S has become a molecule of great interest, and several slow-releasing H(2)S prodrugs are currently under development. We believe that additional agents regulating H(2)S bioavailability will be developed during the next 10 years.