Evolutionary aspects of cytochrome c oxidase

Area of Science:

• Biochemistry
• Molecular Biology
• Evolutionary Biology

Background:

• Cytochrome c oxidase (COX) in eukaryotes has additional subunits compared to bacterial enzymes.
• These subunits increase with organismal evolutionary stage.
• Bacterial COX subunits I-III are mitochondrial DNA-encoded; eukaryotic COX subunits I-III are also mitochondrial DNA-encoded, but additional subunits are nuclear-encoded.

Purpose of the Study:

• To investigate the role of nuclear-coded subunits in mammalian cytochrome c oxidase activity.
• To determine if nuclear-coded subunits influence enzyme kinetics and allosteric regulation.

Main Methods:

• Enzyme activity assays on rat liver COX after dissociation of nuclear-coded subunits using laurylmaltoside and anions.
• Kinetic studies of ferrocytochrome c oxidation using reconstituted COX from bovine heart and P. denitrificans with intraliposomal nucleotides.
• Assessment of tissue-specific allosteric regulation by ADP in reconstituted bovine heart and liver COX.

Main Results:

• Dissociation of nuclear-coded subunits (e.g., VIa) increased rat liver COX activity to levels comparable to bacterial COX.
• Intraliposomal nucleotides influenced the kinetics of reconstituted bovine heart COX but not P. denitrificans COX.
• Reconstituted bovine heart COX showed tissue-specific ADP regulation, unlike bovine liver COX, correlating with differences in subunits VIa, VIIa, and VIII.

Conclusions:

• Nuclear-coded subunits of mammalian cytochrome c oxidase play a crucial role in regulating enzymatic activity.
• These subunits function as receptors for allosteric effectors, modulating the core enzyme's catalytic activity through conformational changes.
• The evolutionary increase in nuclear-coded subunits likely contributes to the fine-tuning of COX function in complex organisms.