Cytochrome C Oxidase (Complex IV)
Definition
The terminal electron acceptor in the mitochondrial respiratory chain, inhibited by both cyanide and hydrogen sulphide. Inhibition prevents oxidative phosphorylation and ATP production, producing cellular asphyxia even when haemoglobin is fully oxygenated.
- Role
- Terminal electron acceptor, mitochondrial respiratory chain
- Inhibited by
- Cyanide and hydrogen sulphide
- Effect
- Blocks oxidative phosphorylation and ATP production
- Result
- Cellular asphyxia despite normal haemoglobin oxygenation
Common questions
Why can a cyanide poisoning victim have normal or even elevated blood oxygen saturation?+
Cyanide blocks the cell's ability to use oxygen at the mitochondrial level rather than preventing oxygen from binding haemoglobin, so oxygen remains in the blood while tissues cannot metabolise it, which is why pulse oximetry can mislead in these cases.
How does this mechanism distinguish chemical asphyxia from carbon monoxide poisoning?+
Carbon monoxide instead binds haemoglobin directly and displaces oxygen transport at the blood level, so the two toxins produce a similar functional outcome of tissue hypoxia through different points of failure in the oxygen delivery and use pathway.
Related terms
- Bitter-Almond Odour
- The characteristic smell of hydrogen cyanide, detectable at autopsy in approximately 40% of people (a genetically determined anosmia to HCN). Present in...
- Carboxyhaemoglobin (COHb)
- The compound formed when carbon monoxide binds to haemoglobin at the oxygen-binding site, with an affinity 200-250 times greater than oxygen. Produces...
- Cherry-Red Livor Mortis
- Bright pink-red post-mortem lividity produced by the spectral absorption shift of carboxyhaemoglobin; also seen in cyanide poisoning and hypothermia. Distinguished from natural...
- Co-Oximetry
- Spectrophotometric analysis of blood that simultaneously quantifies oxyhaemoglobin, deoxyhaemoglobin, carboxyhaemoglobin, methaemoglobin, sulphhaemoglobin, and total haemoglobin by their distinct absorption wavelengths. The primary...
- GC-FID
- Gas chromatography with flame ionisation detection. The standard analytical method for quantifying cyanide and methanol in blood and tissue specimens. Provides both...
- Knockdown Pattern (H2S)
- The scene distribution of multiple H2S victims clustered at the entrance or access point of a confined space, as first responders and...
- Sulphhaemoglobin (SHb)
- A modified haemoglobin species in which one or more pyrrole rings is sulphonated by reaction with hydrogen sulphide. Produces green-brown blood and...