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Table 6 Enzymes of the BChl a biosynthesis pathway that are particularly sensitive to oxygen

From: Inhibition of bacteriochlorophyll biosynthesis in the purple phototrophic bacteria Rhodospirillumrubrum and Rhodobacter capsulatus grown in the presence of a toxic concentration of selenite

Gen name Enzyme name Functional groups sensitive to oxygen
bchI bchD bchH Mg-chelatase BchH contains the particular cystein motif CX2CX3CX14C, which coordinates a [4Fe - 4S] - cluster. This iron - sulfur cluster is particularly sensitive to oxygen and is transformed to a [3Fe - 4S] cluster in its presence. [78].
bchM Mg-PPIX-O-methyltransferase The methyl group is supplied by S - adenosyl - methionine. The oxygen - sensitive BchH has been proposed to be the substrate - binding protein of BchM [79, 80]
bchE Mg - PPIX - O - CH3 oxidative cyclase BchE contains a conserved CX3CX2C cystein motif, which coordinates an oxygen - sensitive [4Fe - 4S] - cluster [77].
bchL bchN bchB Dark allowed protochlorophyllide oxidoreductase (DPOR) The reductase component BchL contains two conserved cysteine residues and the BchL- dimer coordinates an oxygen - sensitive [4Fe - 4S]-cluster [89]. The catalytic component (BchN-BchB)2 also contains conserved cysteines, which coordinate [4Fe - 4S]-clusters, however these are not oxygen-sensitive [129]
bchX bchY bchZ Chlorin reductase (COR) BchX, BchY and BchZ are enzyme subunits structurally and functionally similar to BchL, BchN, and BchB, respectively [90, 91]. It has been shown that the subunit dimers (BchL)2 and (BchX)2 of DPOR and COR, respectively, which drive electrons to the substrates of these enzymes, are exposed to the cytoplasm [91, 92], i.e. to selenite and to the ROS produced during selenite reduction.
  1. Note that each of these enzymes contain SAM, and/or [4Fe-4S] clusters coordinated by cysteine residues, that are potential targets for inactivation by both selenite and the ROS produced during the reduction of selenite to elemental selenium. These potential targets are highlighted using boldface characters