Appearance of nitrite reducing activity of cytochrome c upon heat denaturation.

The research article investigates the emergence of nitrite reducing activity in cytochrome c protein after heat denaturation, using equine heart cytochrome c as a test subject. The researchers found that this change in functionality was based on intrinsic changes within the protein itself, and noted that this biochemical response differs from most other known biological molecules.

Research Methodology and Findings

• The study began by denaturing the cytochrome c (Cyt c) protein found in equine hearts. Denaturing is a process where a protein unravels, losing its specific shape and hence, its function. In this case, the protein was subjected to high temperatures (100 degrees Celsius) for 30 minutes.
• The researchers then found that this denatured cytochrome c (dCyt c), had gained the ability to reduce nitrite ions (NO2-) when combined with dithionite and methylviologen in an aqueous solution under anaerobic conditions.
• By comparison, hemoglobin and myoglobin, two other proteins, were found to not have this same ability under the same conditions, establishing that this property is not a universal response to heat denaturation.
• Using spectroscopic methods, the research team discovered the alterations within the protein that allowed for this newfound ability. These changes included the unfolding of the peptide chain, exposure of the heme group, dissociation of the sixth ligand methionine sulfur, and the presence of autoxidizability.
• Moreover, it was confirmed that the dCyt c catalyzed nitrite reduction to produce ammonium via ferrous-NO complexes by a 6-electron and 8-proton reduction.
• The denatured cytochrome was also immobilized on a Sepharose resin and showed similar nitrite reducing activity. Furthermore, the resin remained active even after being used five times and being stored for up to one year.

Conclusion

• The scientists concluded that the cytochrome c protein can acquire new catalytic activities upon heat treatment. This observed adaptation is unique and uncommon among biological molecules.
• This finding provides new insights into the flexible functionality of proteins and might pave the way for innovative uses of protein denaturation in biotechnology.