title: Cytochromes b561: ascorbate-mediated trans-membrane electron transport.
abstract: CONCLUSIONS
  Cytochromes b561 (CYB561s) constitute a family of trans-membrane (TM), di-heme proteins, occurring in a variety of organs and cell types, in plants and animals, and using ascorbate (ASC) as an electron donor. CYB561s function as monodehydroascorbate reductase, regenerating ASC, and as Fe³⁺-reductases, providing reduced iron for TM transport. A CYB561-core domain is also associated with dopamine β-monooxygenase redox domains (DOMON) in ubiquitous CYBDOM proteins. In plants, CYBDOMs form large protein families. Physiological functions supported by CYB561s and CYBDOMs include stress defense, cell wall modifications, iron metabolism, tumor suppression, and various neurological processes, including memory retention. CYB561s, therefore, significantly broaden our view on the physiological roles of ASC.
  
  
  BACKGROUND
  The ubiquitous nature of CYB561s is only recently being recognized. Significant advances have been made through the study of recombinant CYB561s, revealing structural and functional properties of a unique "two-heme four-helix" protein configuration. In addition, the DOMON domains of CYBDOMs are suggested to contain another heme b.
  
  
  RESULTS
  New CYB561 proteins are still being identified, and there is a need to provide an insight and overview on the various roles of these proteins and their structural properties.
  
  
  CONCLUSIONS
  Mutant studies will reveal in greater detail the mechanisms by which CYB561s and CYBDOMs participate in cell metabolism in plants and animals. Moreover, the availability of efficient heterologous expression systems should allow protein crystallization, more detailed (atomic-level) structural information, and insights into the intra-molecular mechanism of electron transport.
authors.affiliation: Department of Biology, University of Antwerp, Antwerp, Belgium. han.asard@ua.ac.be
authors.forename: Han
authors.initials: H
authors.lastname: Asard
authors.forename: Raffaella
authors.initials: R
authors.lastname: Barbaro
authors.forename: Paolo
authors.initials: P
authors.lastname: Trost
authors.forename: Alajos
authors.initials: A
authors.lastname: Bérczi
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism*; D003573:Cytochrome b Group / Q000737:chemistry / Q000502:physiology*; D004579:Electron Transport; D006801:Humans; D010084:Oxidation-Reduction; D010944:Plants / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D013329:Structure-Activity Relationship
chemical_list: D003573:Cytochrome b Group; C023646:cytochrome b561; D001205:Ascorbic Acid