Characterization of the reaction products of cytochrome c with glutathione by mass spectrometry

Cytochrome c-Capped Fluorescent Gold Nanoclusters: Imaging of Live Cells and Delivery of Cytochrome c

Cytochrome c-capped fluorescent gold nanoclusters (Au-NCs) are used for imaging of live lung and breast cells. Delivery of cytochrome c inside the cells is confirmed by covalently attaching a fluorophore (Alexa Fluor 594) to cytochrome c-capped Au-NCs and observing fluorescence from Alexa 594 inside the cell. Mass spectrometry studies suggest that in bulk water, addition of glutathione (GSH) to cytochrome c-capped Au-NCs results in the formation of glutathione-capped Au-NCs and free apo-cytochrome c. Thus glutathione displaces cytochrome c as a capping agent. Using confocal microscopy, the emission spectra and decay of Au-NCs are measured in live cells. From the position of the emission maximum it is shown that the Au-NCs exist as Au8 in bulk water and as Au13 inside the cells. Fluorescence resonance energy transfer from cytochrome c-Au-NC (donor) to Mitotracker Orange (acceptor) indicates that the Au-NCs localise in the mitochondria of live cells.

The redox state of cytochrome c modulates resistance to methotrexate in human MCF7 breast cancer cells

Background

Methotrexate is a chemotherapeutic agent used to treat a variety of cancers. However, the occurrence of resistance limits its effectiveness. Cytochrome c in its reduced state is less capable of triggering the apoptotic cascade. Thus, we set up to study the relationship among redox state of cytochrome c, apoptosis and the development of resistance to methotrexate in MCF7 human breast cancer cells.

Results

Cell incubation with cytochrome c-reducing agents, such as tetramethylphenylenediamine, ascorbate or reduced glutathione, decreased the mortality and apoptosis triggered by methotrexate. Conversely, depletion of glutathione increased the apoptotic action of methotrexate, showing an involvement of cytochrome c redox state in methotrexate-induced apoptosis. Methotrexate-resistant MCF7 cells showed increased levels of endogenous reduced glutathione and a higher capability to reduce exogenous cytochrome c. Using functional genomics we detected the overexpression of GSTM1 and GSTM4 in methotrexate-resistant MCF7 breast cancer cells, and determined that methotrexate was susceptible of glutathionylation by GSTs. The inhibition of these GSTM isoforms caused an increase in methotrexate cytotoxicity in sensitive and resistant cells.

Conclusions

We conclude that overexpression of specific GSTMs, GSTM1 and GSTM4, together with increased endogenous reduced glutathione levels help to maintain a more reduced state of cytochrome c which, in turn, would decrease apoptosis, thus contributing to methotrexate resistance in human MCF7 breast cancer cells.

Studies of interaction between insulin and glutathione using electrospray ionization mass spectrometry

RATIONALE

The interaction of glutathione (GSH) with insulin plays an important role in the degradation or regulation of insulin. The characterization of the reaction products of GSH and insulin is very important for a proper understanding of the mechanism of insulin regulation of GSH.

METHODS

Solutions of insulin and glutathione were incubated under different experimental conditions in vitro. The reaction products were determined by electrospray ionization (ESI) ion trap mass spectrometry combined with Fourier transform ion cyclotron resonance (FTICR) mass spectrometry.

RESULTS

The multi-reaction products were identified, including insulin A chain with two intrachain disulfides, insulin B chain with one intrachain disulfides, GSH-modified insulin, GSH-modified A chain, GSH-modified B chain, aggregates of A chain and B chain, and reduced A chain and B chain. The binding site of the B chain with insulin was determined directly by tandem mass spectrometry (MS/MS) without enzyme digestion. It was found that the reaction between GSH and insulin was pH-, O(2)- and temperature-dependent.

CONCLUSIONS

The results provide insight into the interaction between GSH and insulin. It has also been demonstrated that ESI-MS combined with high-resolution FTICRMS and MS/MS provides a powerful tool for screening the reactions of proteins and small molecules.

A novel role for cytochrome c: Efficient catalysis of S-nitrosothiol formation

Although S-nitrosothiols are regarded as important elements of many NO-dependent signal transduction pathways, the physiological mechanism of their formation remains elusive. Here, we demonstrate a novel mechanism by which cytochrome c may represent an efficient catalyst of S-nitrosation in vivo. In this mechanism, initial binding of glutathione to ferric cytochrome c is followed by reaction of NO with this complex, yielding ferrous cytochrome c and S-nitrosoglutathione (GSNO). We show that when submitochondrial particles or cell lysates are exposed to NO in the presence of cytochrome c, there is a robust formation of protein S-nitrosothiols. In the case of submitochondrial particles protein S-nitrosation is paralleled by an inhibition of mitochondrial complex I. These observations raise the possibility that cytochrome c is a mediator of S-nitrosation in biological systems, particularly during hypoxia, and that release of cytochrome c into the cytosol during apoptosis potentially releases a GSNO synthase activity that could modulate apoptotic signaling.

Nitrite anions induce nitrosative deamination of peptides and proteins

In the present study, reactions of sodium nitrite with proteins/peptides were characterized with mass spectrometry. The reaction generates two major products: replacement of the amino group by a hydroxyl group and formation of an alkene derivative by loss of a NH3 group at the N-terminus and the side chain of lysine residues of proteins/peptides. The reaction proceeds rapidly in weak acidic solution and at 37 degrees C in the presence of a millimolar concentration of nitrite, demonstrating that nitrite induces nitrosative deamination in proteins and peptides. The facile nitrite-induced modification of amino groups of protein/peptides changes the chemical nature of proteins and may have various applications in peptide synthesis, analytical chemistry, and protein engineering. It also provides information to enhance our understanding of functions of nitrite ions in biology and food preservation.