- any of several carrier molecules in the mitochondria of plant and animal cells, consisting of a protein and an iron-containing porphyrin ring and participating in the stepwise transfer of electrons in oxidation reactions: each cytochrome alternately accepts and releases an electron at a slightly lower energy level in the order designated b, c1, c, a, and a3.
- any of a group of naturally occurring compounds, consisting of iron, a protein, and a porphyrin, that are important in cell oxidation-reduction reactions
