Euglena gracilis complex III prepared from its submitochondrial particles showed an atypical difference absorption spectrum for cytochrome c1 with α-peak at 561 nm. Pyridine ferrohemochrome of cytochrome c1 showed its α-peak at 553 nm. The amino-terminal sequence of cytochrome c1 suggested that its heme moiety was covalently linked to cysteine-39 through a single thioether bond. Phenylalanine occupied position 36 usually occupied by cysteine affording the other thioether bond. The total amino acid sequence of mature cytochrome c1 was determined by sequencing of its cDNA. The cDNA clone consisted of 872 base pairs encoding the mature protein with 243 amino acids. The putative sequence contained an unusual heme binding sequence, -F-A-P-C-H-, instead of the typical sequence, -C-X-Y-C-H-, found in other eukaryotic C-type cytochromes. Sequence comparison, gene manipulation, and physical studies indicated the heme ligands and a binding site to cytochrome c.
KeywordsHeme Iron Euglena Gracilis Submitochondrial Particle Horse Heart Cytochrome Thioether Bond
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