An Arabidopsis cytochrome b561 with trans‐membrane ferrireductase capability

Abstract

Ascorbate-reducible cytochromes b561 (Cyts-b561) are a class of intrinsic trans-membrane proteins. Tonoplast Cyt-b561 (TCytb), one of the four Cyt-b561 isoforms in Arabidopsis was localized to the tonoplast. We demonstrate here that the optical spectra, EPR spectra and redox potentials of recombinant TCytb are similar to those of the well characterized bovine chromaffin granule Cyt-b561. We provide evidence for the reduction of ferric-chelates by the reduced TCytb. It is also shown that TCytb is capable of trans-membrane electron transport from intracellular ascorbate to extracellular ferric-chelates in yeast cells.

The Bradyrhizobium japonicum frcB Gene Encodes a Diheme Ferric Reductase

“…Oxidation of FrcB was discerned spectrophotometrically by comparing the reduced sample to that oxidized by FeCl 3 . Dithionite (final concentration of 200 M) was added to 20 M protein.…”

“…The mammalian heme protein Dcytb is expressed under iron-limiting conditions in duodenal cells (22). Homologs of Dcytb are found in other mammalian cell types as well as other eukaryotic species (3,4,13,36,42). Although Fre1 and Dcytb have been well described and are necessary for ferric iron reduction in whole cells, ferric reductase activity has not been demonstrated in the purified proteins.…”

Dihydrolipoic acid reduces cytochrome b561 proteins

“…It seems that other members of the protein family are present in a very small amount in their natural sources and appropriate amounts of these Cyt-b561 proteins could be obtained only after establishing a heterologous expression system for producing recombinant Cyt-b561 proteins. Such expression systems were developed and successfully used in the characterization of CGCB (Bérczi et al 2005;Liu et al 2005Liu et al , 2007, of the duodenum-localized Cyt-b561 (DCB; Ludwiczek et al 2008;Oakhill et al 2008), of the lysosome-localized Cyt-b561 (LCB; Zhang et al 2006), of the putative tumour suppressor Cytb561 (TSCB; Mizutani et al 2007;Bérczi and Asard 2008;Recuenco et al 2009), and of the tonoplast-localized Cyt-b561 (TCB; Griesen et al 2004;Bérczi et al 2007;Cenacchi et al 2011) in the last 10 years. Only speculations exist, however, for the biological function of Cyt-b561 proteins other than CGCB and DCB (e.g.…”

“…Although the amino acids of the two interloop regions between TM2 and TM3 as well as between TM4 and TM5 ( proteins, possibly resulting in significant differences in the location and shape of the split α-band of the HA-side hemes. We should also recall that there is a significant difference between the location of the EPR signal attributed to the HA-side heme in TCB and TSCB (Bérczi et al 2007(Bérczi et al , 2010Desmet et al 2011). While g z =3.14 (Bérczi et al 2007) and g z =3.16 (Desmet et al 2011) was obtained for the HA-side heme in TCB in sucrose monolaurate and DM micelles, respectively, a considerably lower value of g z =2.96 (Bérczi et al 2010) LA/DHLA has recently gained substantial interest in biochemistry, food and pharmaceutical sciences as antioxidant, nutritional supplement and therapeutic agent (Packer et al 1996(Packer et al , 1997Li et al 2004;Han et al 2008).…”

Direct Recording of Trans-Plasma Membrane Electron Currents Mediated by a Member of the Cytochrome b561 Family of Soybean

“…CYB561 of chromaffin granules in mammals reduces intravesicular MDHA to sustain ASC-dependent catecholamine biosynthesis (Njus and Kelley, 1993), and a similar MDHA reductase activity was demonstrated in several CYB561 plant isoforms (Horemans et al, 1994;Nakanishi et al, 2009;Asard et al, 2013). On the other hand, the activity of plant CYB561 with ferrichelates (Bérczi et al, 2007) recalls the activity of a duodenal CYB561 isoform (duodenal cytochrome b564 [Dcytb]) of mammals that performs the ASC-dependent reduction of ferric chelates derived from the diet, allowing the absorption of ferrous iron by divalent metal transporters (McKie et al, 2001). In several instances, both in plants and animals, single CYB561 isoforms proved capable of reducing both MDHA and ferrichelates, leaving some uncertainty about their specific role in vivo (Asard et al, 2013).…”