Molybdenum transport in plants and animals
See also molybdoenzymes, molybdenum storage proteins, molybdo-pterin, Mo co-factor
Molybdenum transport as molybdate and comparison with sulfate. Preventing extracellular uptake by complexing.
It is likely that molybdenum is taken up and transported in plants and animals in the form of the simple molybdate ion [MoO4]2-. In sheep [Scaife, 1956] molybdenum in the blood and urine is readily dialysable and is entirely anionic. A study of molybdenum toxicity in the microorganism Salmonella typhimurium has indicated that molybdate and sulfate are transported in the same system [McKillen and Spencer, 1970]. In this organism uptake of molybdenum and molybdenum toxicity are prevented by complexing of extracellular molybdate with L-cysteine and reduced glutathione. However, it has also been suggested that in the microorganism Aspergillus nidulans molybdenum is taken up in a phosphorylated entity and a carbohydrate [Arst et al., 1970; Arst and Cove, 1970]. The following chelating agents have been reported to be effective against molybdenum toxicity in mice (presumably because they coordinate with the molybdate ion): ethylenediaminetetraacetate, diethylenetriaminepentaacetate, unithiol and deoxycholate [Chem. Abs,1971]
Scaife, J. F., New Zealand J. Sci. Technol., 1956, 38A ,293.
McKillen, M. N.and Spencer, B., Biochem. J., 1970, 118 , 27.
Arst, H. N., MacDonald, D. W. and Cove, D. J., Mol. Gen. Genet., 1970, 108 , 129.
Arst, H. N. and Cove, D. J., Mol. Gen. Genet., 1970, 108 , 146.Chem. Abs., 1971, 74 , 99958u.
Multiplicity of Sulfate and Molybdate Transporters and Their Role in Nitrogen Fixation in Rhizobium leguminosarum bv. viciae Rlv3841
Rhizobium leguminosarum Rlv3841 contains at least three sulfate transporters, i.e., SulABCD, SulP1 and SulP2, and a single molybdate transporter, ModABC. SulABCD is a high-affinity transporter whose mutation prevented growth on a limiting sulfate concentration, while SulP1 and SulP2 appear to be low-affinity sulfate transporters. ModABC is the sole high-affinity molybdate transport system and is essential for growth with NO3- as a nitrogen source on limiting levels of molybdate (molybdate, a quadruple mutant with all four transporters inactivated, had the longest lag phase on NO3-, suggesting these systems all make some contribution to molybdate transport. Growth of Rlv3841 on limiting levels of sulfate increased sulB, sulP1, modB, and sulP2 expression 313.3-, 114.7-, 6.2-, and 4.0-fold, respectively, while molybdate starvation increased only modB expression (three- to 7.5-fold). When grown in high-sulfate but not low-sulfate medium, pea plants inoculated with LMB695 (modB) reduced acetylene at only 14% of the wild-type rate, and this was not further reduced in the quadruple mutant. Overall, while modB is crucial to nitrogen fixation at limiting molybdate levels in the presence of sulfate, there is an unidentified molybdate transporter also capable of sulfate transport.
Cheng, G., Karunakaran, R., East, A. K., and Poole, P. S.,Multiplicity of Sulfate and Molybdate Transporters and Their Role in Nitrogen Fixation in Rhizobium leguminosarum bv. viciae Rlv3841, Molecular plant-microbe interactions : MPMI, 2016, 29, 143-52.
Microbial ligand coordination: Consideration of biological significance
Siderophores are generally considered to be microbial chelating compounds secreted by bacteria to facilitate uptake of iron(III). Certain siderophores, however, have a high affinity for other transition metal ions, including manganese(III), copper(II), molybdenum(VI), and vanadium(V). A new class of microbial ligands produced by methanotrophs, called chalkophores, is produced to facility copper uptake.
This review considers the coordination of siderophores to Mn(III), Cu(II/I), Mo(VI) and V(V), and their stability constants relative to Fe(III), when available, as well as the coordination complexes of chalkophores to Cu( l). (C) 2015 Elsevier B.V. All rights reserved.
Springer, S. D., and Butler, A.,Microbial ligand coordination: Consideration of biological significance, Coordination Chemistry Reviews, 2016, 306, 628-635.