Bovine complex I is a complex of 45 different subunits.
Mammalian mitochondrial complex I is a multisubunit membrane-bound assembly with a molecular mass approaching 1 MDa. By comprehensive analyses of the bovine complex and its constituent subcomplexes, 45 different subunits have been characterized previously. The presence of a 46th subunit was suspected from the consistent detection of a molecular mass of 10,566 by electrospray ionization mass spectrometry of subunits fractionated by reverse-phase high pressure liquid chromatography. The component was found associated with both the intact complex and subcomplex Ibeta, which represents most of the membrane arm of the complex, and it could not be resolved chromatographically from subunit SGDH (the subunit of bovine complex I with the N-terminal sequence Ser-Gly-Asp-His). It has now been characterized by tandem mass spectrometry of intact protein ions and shown to be a C-terminal fragment of subunit SGDH arising from a specific peptide bond cleavage between Ile-55 and Pro-56 during the electrospray ionization process. Thus, the subunit composition of bovine complex I has been established. It is a complex of 45 different proteins plus non-covalently bound FMN and eight iron-sulfur clusters.
Carroll
Joe
J
Dunn Human Nutrition Unit, The Medical Research Council, Hills Road, Cambridge CB2 2XY, United Kingdom.
Fearnley
Ian M
IM
Skehel
J Mark
JM
Shannon
Richard J
RJ
Hirst
Judy
J
Walker
John E
JE
D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D042967:Electron Transport Complex I / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification; D008929:Mitochondria, Heart / Q000737:chemistry; D008970:Molecular Weight; D021122:Protein Subunits / Q000302:isolation & purification; D021241:Spectrometry, Mass, Electrospray Ionization
D021122:Protein Subunits; D042967:Electron Transport Complex I