TY - JOUR
T1 - Stability constants of the fungal siderophore rhizoferrin with various microelements and calcium
AU - Shenker, M.
AU - Hadar, Y.
AU - Chen, Y.
PY - 1996
Y1 - 1996
N2 - Stability constants of metal-ligand complexes determine their speciation in solution at equilibrium. Therefore, stability constants of siderophore-metal complexes are of crucial importance in studies of their efficiency as Fe mediators. In this study, potentiometric titrations were used to determine protonation and stability constants of Fe3+, Fe2+, Cu2+, Ca2+, and Zn2+ with rhizoferrin, a siderophore produced by Rhizopus arrhizus, which has been shown in previous studies to be an effective carrier of Fe to plants. Rhizoferrin was found to be a specific Fe3+ chelator but with a stability constant lower than most microbial siderophores. The ferric complex of rhizoferrin is anionic throughout the pH range prevailing in soils, and therefore, it is expected to be mobile in the rhizosphere. The following log K(app) values at 25°C, pH 7.0, and 0.1 M ionic strength were determined: 19.1, 7.5, 6.2, 6.0, and 4.4 for Fe3+, Fe2+, Cu2+, Ca2+, and Zn2+, respectively. The apparent stability constant (K(app)) value for the ferric complex of rhizoferrin suggests that ligand exchange with mugineic acid is the mechanism facilitating the efficiency of rhizoferrin as an Fe carrier to graminaceous plants.
AB - Stability constants of metal-ligand complexes determine their speciation in solution at equilibrium. Therefore, stability constants of siderophore-metal complexes are of crucial importance in studies of their efficiency as Fe mediators. In this study, potentiometric titrations were used to determine protonation and stability constants of Fe3+, Fe2+, Cu2+, Ca2+, and Zn2+ with rhizoferrin, a siderophore produced by Rhizopus arrhizus, which has been shown in previous studies to be an effective carrier of Fe to plants. Rhizoferrin was found to be a specific Fe3+ chelator but with a stability constant lower than most microbial siderophores. The ferric complex of rhizoferrin is anionic throughout the pH range prevailing in soils, and therefore, it is expected to be mobile in the rhizosphere. The following log K(app) values at 25°C, pH 7.0, and 0.1 M ionic strength were determined: 19.1, 7.5, 6.2, 6.0, and 4.4 for Fe3+, Fe2+, Cu2+, Ca2+, and Zn2+, respectively. The apparent stability constant (K(app)) value for the ferric complex of rhizoferrin suggests that ligand exchange with mugineic acid is the mechanism facilitating the efficiency of rhizoferrin as an Fe carrier to graminaceous plants.
UR - http://www.scopus.com/inward/record.url?scp=0029664078&partnerID=8YFLogxK
U2 - 10.2136/sssaj1996.03615995006000040026x
DO - 10.2136/sssaj1996.03615995006000040026x
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AN - SCOPUS:0029664078
SN - 0361-5995
VL - 60
SP - 1140
EP - 1144
JO - Soil Science Society of America Journal
JF - Soil Science Society of America Journal
IS - 4
ER -