Reorganization of immobilized horse and yeast cytochrome c induced by pH changes or nitric oxide binding.

This research explores how changes in pH or the binding of nitric oxide affect the redox properties, or the electron transferring capability, of horse and yeast cytochrome c, a vital protein found in many organisms. These proteins were immobilized on a surface that can change its properties along with variations in pH. The results showed that the properties of yeast cytochrome c change after pH 6, while those of horse cytochrome c did not. The presence of nitric oxide slowed the electron-transfer rates in both cytochromes, probably induced by a change in the protein’s structure.

Cytochrome c and Redox Properties

• The study investigates horse and yeast cytochrome c, essential proteins playing crucial roles in electron transfer, specifically their redox properties, which are their capabilities to accept and donate electrons.
• The proteins are immobilized on carboxylic acid-terminated self-assembled monolayers (SAMs), a surface that is often used to observe the changes in the properties of immobilized particles.
• The aim is to study the behavior of these proteins across a wide range of pH (from pH 3.5 to 8), both in the absence and presence of nitric oxide, which plays a role in multiple cellular processes.

pH-Induced Changes in Cytochrome c

• Until about pH 6, both horse and yeast cytochrome c show similar behaviors in terms of midpoint potentials, coverages, and electron-transfer rate constants. This suggests that the proteins interact with the SAM surface similarly within this pH range.
• However, once the pH crosses 6, a notable decrease in electron-transferring rates is observed in yeast cytochrome c — a sign of a change in the electron tunneling pathway between the iron-containing heme of the protein and the electrode.
• This suggests the yeast protein reorients or changes position on the surface when the pH rises. Horse cytochrome c, however, does not exhibit such a change, pointing towards a specific charge distribution in yeast cytochrome c contributing to this behavior.

Impact of Nitric Oxide

• Adding nitric oxide to the environment also influences the electron-transfer rates. In the case of both yeast and horse cytochrome c, it resulted in a decrease in these rates at lower pH levels.
• This decrease may stem from nitric oxide inducing a conformational or structural change in the protein, affecting how it transfers electrons. Nitric oxide also seems to alter the reorganization energy for electron transfer, which means that it impacts the movement or realignment of charges during this process.

Key Findings and Impact

• This research points out key differences in how horse and yeast cytochrome c react to variations in pH and the presence of nitric oxide. It also suggests how the specific charge distribution on these proteins and their environment plays a role in their electron transferring capabilities.
• Given that cytochrome c plays crucial roles in many processes, such as cellular respiration and apoptosis, this understanding of its behavior in changing environments could further its respective field and create potential applications or therapies.