Modification of the structural and redox properties of cytochrome c by heteropolytungstate binding.

This research explores the changes in structure and redox properties that occur in Cytochrome c, a key protein, when it interacts with large three-dimensional polyanions. The study reveals that the protein’s structure and properties are affected by the characteristics of the particle it binds with, as well as the pH and ionic strength of the surrounding environment.

Research Methodology

• The research studied the interplay between horse heart ferricytochrome c and different-sized polyanions to understand how surface electrostatic interactions can influence the cytochrome c’s structural and redox properties.
• They observed the way cytochrome c binds with large heteropolytungstates, such as (NaSb9W21O86)18- and (KAs4W40O140)27-, and a smaller ion (SiW11O39)8-. These ratios of interaction were 1/1 for larger polyanions, and 2/1 for the smaller ion.
• The environment’s pH and ionic strength, along with the polyanion’s size and charge, played a significant role in the structural changes of cytochrome c upon complexation.

Findings of the Research

• Three distinct forms of the complexed cytochrome c were detected using optical and EPR spectroscopies over a pH range of 6.5 to 8. These forms are dubbed as N, A and B forms.
• The N form is closely associated with the native structure of the protein, while the A form replicates cytochrome c in acidic conditions. The B form is a new discovery where the ‘heme’ pocket of the protein is open, but the iron it contains remains low-spin.
• The research uncovered that the redox potential of cytochrome c drops to 250-220 mV (compared to Normal Hydrogen Electrode, NHE) in the N form, and even further down to 80mV in the B form.
• This implies that the structure and redox properties of cytochrome c can be significantly influenced by the characteristics of the particles it binds with and the surrounding environmental conditions.