Cobalt-cytochrome c. I. Preparation, properties, and enzymic activity

Area of Science:

• Biochemistry
• Bioinorganic Chemistry

Background:

• Cytochrome c is a vital protein in cellular respiration.
• Cobalt substitution offers a tool to probe protein function and electron transfer mechanisms.

Purpose of the Study:

• To develop an improved method for preparing cobalt-cytochrome c.
• To characterize the properties of cobalt-cytochrome c and its interactions with enzymes.

Main Methods:

• Improved cobalt insertion procedure.
• Optical spectroscopy for characterizing cobalt-cytochrome c.
• Enzymatic assays to assess oxidation-reduction rates.

Main Results:

• Cobalt-cytochrome c is a six-coordinated species with distinct spectral properties.
• Cobalt-cytochrome c exhibits a significantly lower redox potential (Em,7 = -140 mV) compared to native ferrocytochrome c (Em,7 = +250 mV).
• Cobalt-cytochrome c is oxidized by cytochrome oxidase at 45% of the native rate but is not reduced by key reductase enzymes, indicating altered binding sites.

Conclusions:

• Cobalt substitution modifies the stereoelectronic interactions within cytochrome c.
• The reductase binding site integrity is compromised, while the oxidase binding site is modified.
• Cobalt-cytochrome c serves as a valuable probe for understanding electron transfer pathways and enzyme interactions.