MetaCyc Polypeptide: light-independent protochlorophyllide reductase subunit N

Gene: bchN Accession Number: G-10103 (MetaCyc)

Synonyms: LI-POR subunit N, DPOR subunit N

Species: Rhodobacter capsulatus

Component of:
NB protein
light-independent protochlorophyllide reductase (extended summary available)

Gene Citations: [Youvan84, Youvan84a, Bauer88]

Molecular Weight of Polypeptide: 45.83 kD (from nucleotide sequence), 52 kD (experimental) [Nomata05 ]

Unification Links: DIP:DIP-59277N , Protein Model Portal:P26164 , UniProt:P26164

Relationship Links: Entrez-Nucleotide:RELATED-TO:Z11165 , InterPro:IN-FAMILY:IPR000510 , InterPro:IN-FAMILY:IPR005970 , PDB:Structure:3AEK , PDB:Structure:3AEQ , PDB:Structure:3AER , PDB:Structure:3AES , PDB:Structure:3AET , PDB:Structure:3AEU , Pfam:IN-FAMILY:PF00148

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Subunit of: NB protein

Species: Rhodobacter capsulatus

Subunit composition of NB protein = [BchB]2[BchN]2
         light-independent protochlorophyllide reductase subunit B = BchB
         light-independent protochlorophyllide reductase subunit N = BchN

Component of: light-independent protochlorophyllide reductase (extended summary available)

Molecular Weight: 200 kD (experimental) [Nomata05]

Created 19-Jul-2007 by Caspi R , SRI International

Subunit of: light-independent protochlorophyllide reductase

Species: Rhodobacter capsulatus

Subunit composition of light-independent protochlorophyllide reductase = [(BchL)2][(BchB)2(BchN)2]
         bchL dimer = (BchL)2
                 light-independent protochlorophyllide reductase subunit L = BchL
         NB protein = (BchB)2(BchN)2
                 light-independent protochlorophyllide reductase subunit B = BchB
                 light-independent protochlorophyllide reductase subunit N = BchN

There are two different enzymes system that can catalyze the reduction of protochlorophyllide a to chlorophyllide a - a light-independent enzyme and a light-dependent enzyme. The light-dependent enzyme is present in all oxygenic phototrophs (see protochlorophyllide oxidoreductase from Arabidopsis thaliana col for example). The light-independent enzyme is found in all photosynthetic bacteria (including cyanobacteria), algae and gymnosperms. Many organisms possess both enzymes [Bollivar06]. The possession of the light-independent enzyme permits the organism to synthesize chlorophyll (or bacteriochlorophyll) in the dark.

The Rhodobacter capsulatus enzyme is composed of three subunits, encoded by the bchB, bchL and bchN genes. Initial work indicated that the bchL gene product is necessary for protochlorophillde reductase function [Yang90]. Subsequent work revealed the identity of the other two subunits [Burke93, Bollivar94].

The enzyme is very similar to the nitrogenase enzyme system. This similarity helped form an assay for the enzyme activity, and facilitated its characterization [Nomata05]. The three components were over-expressed, purified, and combined in vitro. Gel filtration chromatography indicated that the N and B proteins form a heterotetrameric complex [(BchN)2(BchB)2], known as the NB protein, and that the L-protein exists as a homodimer.

The Vmax for the complex was determined to be 232 pmol/min/mg protein.

The crystal structure of the NB protein was obtained at a resolution of 2.3Å. Each catalytic BchN-BchB unit contains one Pchlide and one iron-sulfur cluster [Muraki10].

Created 19-Jul-2007 by Caspi R , SRI International

Enzymatic reaction of: light-independent protochlorophyllide reductase

EC Number:

chlorophyllide a + 2 an oxidized ferredoxin + 2 ADP + 2 phosphate <=> protochlorophyllide a + 2 a reduced ferredoxin + 2 ATP + 2 H2O

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the opposite direction.

In Pathways: superpathway of bacteriochlorophyll a biosynthesis , chlorophyllide a biosynthesis II (anaerobic)

Cofactors or Prosthetic Groups: a [4Fe-4S] iron-sulfur cluster [Nomata05]

Kinetic Parameters:

Km (μM)
protochlorophyllide a


Bauer88: Bauer CE, Young DA, Marrs BL (1988). "Analysis of the Rhodobacter capsulatus puf operon. Location of the oxygen-regulated promoter region and the identification of an additional puf-encoded gene." J Biol Chem 263(10);4820-7. PMID: 3127391

Bollivar06: Bollivar DW (2006). "Recent advances in chlorophyll biosynthesis." Photosynth Res 90(2);173-94. PMID: 17370354

Bollivar94: Bollivar DW, Suzuki JY, Beatty JT, Dobrowolski JM, Bauer CE (1994). "Directed mutational analysis of bacteriochlorophyll a biosynthesis in Rhodobacter capsulatus." J Mol Biol 237(5);622-40. PMID: 8158642

Burke93: Burke DH, Alberti M, Hearst JE (1993). "bchFNBH bacteriochlorophyll synthesis genes of Rhodobacter capsulatus and identification of the third subunit of light-independent protochlorophyllide reductase in bacteria and plants." J Bacteriol 175(8);2414-22. PMID: 8385667

Muraki10: Muraki N, Nomata J, Ebata K, Mizoguchi T, Shiba T, Tamiaki H, Kurisu G, Fujita Y (2010). "X-ray crystal structure of the light-independent protochlorophyllide reductase." Nature 465(7294);110-4. PMID: 20400946

Nomata05: Nomata J, Swem LR, Bauer CE, Fujita Y (2005). "Overexpression and characterization of dark-operative protochlorophyllide reductase from Rhodobacter capsulatus." Biochim Biophys Acta 1708(2);229-37. PMID: 15953479

Yang90: Yang ZM, Bauer CE (1990). "Rhodobacter capsulatus genes involved in early steps of the bacteriochlorophyll biosynthetic pathway." J Bacteriol 172(9);5001-10. PMID: 2203738

Youvan84: Youvan DC, Alberti M, Begusch H, Bylina EJ, Hearst JE (1984). "Reaction center and light-harvesting I genes from Rhodopseudomonas capsulata." Proc Natl Acad Sci U S A 81(1);189-192. PMID: 16593406

Youvan84a: Youvan DC, Bylina EJ, Alberti M, Begusch H, Hearst JE (1984). "Nucleotide and deduced polypeptide sequences of the photosynthetic reaction-center, B870 antenna, and flanking polypeptides from R. capsulata." Cell 37(3);949-57. PMID: 6744416

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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