The binding of aluminum to mugineic acid and related compounds as studied by potentiometric titration

Abstract

The phytosiderophores, mugineic acid (MA) and epi-hydroxymugineic acid (HMA), together with a related compound, nicotianamine (NA), were investigated for their ability to bind Al(III). Potentiometric titration analysis demonstrated that MA and HMA bind Al(III), in contrast to NA which does not under normal physiological conditions. With MA and HMA, in addition to the Al complex (AlL), the protonated (AlLH) and deprotonated (AlLH(-1)) complexes were identified from an analysis of titration curves, where L denotes the phytosiderophore form in which all the carboxylate functions are ionized. The equilibrium formation constants of the Al(III) phytosiderophore complexes are much smaller than those of the corresponding Fe(III) complexes. The higher selectivity of phytosiderophores for Fe(III) over Al(III) facilitates Fe(III) acquisition in alkaline conditions where free Al(III) levels are higher than free Fe(III) levels.

Isotope fractionation of zinc in the paddy rice soil-water environment and the role of 2’deoxymugineic acid (DMA) as zincophore under Zn limiting conditions

“…were statistically significant (n≥2 biological replicates), we used a t-test for unequal sample The pK a1 (3.10±0.01) corresponds to the proton dissociation of the terminal carboxylic group while pK a2 (7.97±0.01) and pK a3 (10.94±0.01) refer to the dissociation of protons from the secondary amine and the tertiary amine of the azetidine ring, respectively (Murakami et al, 1989) (see Figure 2). The proton that belongs to the terminal alcoholic group is only released in the presence of trivalent cations, as demonstrated using potentiometric titrations of Fe 3+ and Al 3+ with DMA (Yoshimura et al, 2011) and an X-ray crystal structure of a Co 3+ complex with MA (Mino et al, 1981). The proton dissociation on the other two carboxyl are difficult to measure because they are very low (pK<2, see Figure 2).…”

“…* Data retrieved from figures. (Murakami et al, 1989;Sugiura and Nomoto, 1984;Yoshimura et al, 2011). All studies used ligand material isolated from root washings to conduct measurements of complex stabilities.…”

Metallophores and Trace Metal Biogeochemistry

“…1), which is a surrogate for a metal ion's hardness (Duckworth et al 2009bHernlem et al 1999;Hider 1984). The difficulty in overcoming this trend in affinity in favor of a target metal is illustrated by the Table 1 Selected logb for a selection of metallophores with diverse metal ions Anderegg et al 1963;Bellenger et al 2007;Buglyo et al 1995;Carrano et al 1996;Choi et al 2006;Duckworth et al 2009c;Duckworth and Sposito 2005b;Enyedy et al 2004;Evers et al 1989;Farkas et al 2003;Harrington et al 2012b;Hernlem et al 1996;Jarvis and Hancock 1991;Kim et al 2009;Murakami et al 1989;Pesch et al 2012;Shenker et al 1996;Szabo and Farkas 2011;Whisenhunt et al 1996;Yoshimura et al 2011 …”

Distinct catalytic capacities of two aluminium-repressed Arabidopsis thaliana xyloglucan endotransglucosylase/hydrolases, XTH15 and XTH31, heterologously produced in Pichia

“…S2), enzymes that produce the secreted phytosiderophore, nicotianamine. This C 12 compound, synthesised from S-adenosylmethionine, complexes with several divalent metal ions and also with Fe 3+ , though apparently not strongly with Al 3+ (Yoshimura et al, 2011). In grasses, nicotianamine is a precursor of mugineic acid, a phytosiderophore that does complex with Al 3+ ; however, mugineic acid does not appear to occur in dicots such as Arabidopsis (Haydon and Cobbett, 2007).…”