cytochrome b6f complex

GO:0009512 · Energy complex · Multiprotein complex · Proposed

A thylakoid membrane protein complex that oxidizes plastoquinol, reduces a downstream soluble electron carrier for photosystem I, and contributes to proton translocation during oxygenic photosynthetic electron transport. [GO:0009512]

Part of: thylakoid membrane (GO:0042651)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Taxonomic distribution

• NCBITaxon:1117 Cyanobacteriota — COMMON: Cyanobacteria with internal thylakoids use cytochrome b6f as a major thylakoid electron-transport complex between plastoquinol and PSI. [DOI:10.1146/annurev-cellbio-120823-022747]

Canonical examples

• NCBITaxon:103690 Nostoc sp. PCC 7120 = FACHB-418 — Cyanobacterial model used to purify and determine the crystal structure of a stable dimeric cytochrome b6f complex. [DOI:10.1074/jbc.M809196200]

Functions

• photosynthetic electron transport chain GO:0009767 — Cytochrome b6f oxidizes plastoquinol downstream of PSII, reduces a soluble carrier for PSI, and couples that electron flow to thylakoid proton translocation.
  • GO:0009512 GO:0009512 defines the cytochrome b6f complex by electron transfer from reduced plastoquinone to oxidized plastocyanin with coupled proton translocation.
  • DOI:10.1146/annurev-cellbio-120823-022747 Perez-Boerema et al. 2024 place cytochrome b6f between PSII and PSI in the thylakoid electron-transport chain.

Mechanism graphs

Cytochrome b6f couples thylakoid quinol oxidation to proton transfer (FUNCTION)

In oxygenic thylakoid electron transport, cytochrome b6f receives electrons from the plastoquinone pool, passes them toward PSI through a soluble carrier, and contributes to the proton motive force.

Discussions

• CURATION_TODO (OPEN): Resolve exact source-neutral component groundings for cytochrome b6f core, Rieske, and small subunit families before adding subunit-level component rows. GO exactly grounds the complete b6f complex, but this first record does not yet distinguish conserved b6f constituents from bound cofactors, lipids, or organism-specific soluble electron carriers.

Evidence

• GO:0009512 Gene Ontology cellular-component term for the cytochrome b6f complex.
• GO:0042651 Gene Ontology cellular-component term for the thylakoid membrane that houses photosynthetic electron-transport complexes.
• GO:0009767 Gene Ontology biological-process term for the photosynthetic electron transport chain.
• DOI:10.1146/annurev-cellbio-120823-022747 Perez-Boerema et al. 2024, Evolution of Thylakoid Structural Diversity, Annual Review of Cell and Developmental Biology.
• DOI:10.1074/jbc.M809196200 Baniulis et al. 2009, Structure-Function, Stability, and Chemical Modification of the Cyanobacterial Cytochrome b6f Complex from Nostoc sp. PCC 7120, Journal of Biological Chemistry.

Curation history

• 2026-09-13T05:42:11Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
• 2026-09-13T05:42:57Z codex · EXPANDED_RECORD — Added thylakoid membrane parthood, cyanobacterial scope, a Nostoc canonical example, photosynthetic electron-transport function, GO and literature evidence, a nonmechanistic b6f electron/proton-coupling graph, and a b6f subunit-boundary TODO.
• 2026-09-13T05:43:22Z codex · REVISED_GRAPH_EVIDENCE — Replaced GO-only evidence on the b6f electron-transport graph edge with literature evidence for the process claim.

Source: data/structures/energy_complex/cytochrome_b6f_complex.yaml