Thomas Emery

Iron oxidation by casein

Casein accelerates the oxidation of Fe(II) to Fe(III) and the resulting Fe(III) remains strongly bound to the casein. Removal of phosphate from the casein abolishes the oxidative process. The oxidation rate is proportional to the casein concentration, and with high casein concentrations the rate is pseudo-first-order with respect to Fe(II) with a half-life of approximately 2 minutes. The oxidized iron is stoichiometrically bound to the casein, each mg of casein binding approximately 10 micrograms of iron. The physiological significance is discussed.

Malonichrome, a new iron chelate from Fusarium roseum

The predominant iron chelates, or siderochromes, produced by the fungus, Fusarium roseum during culture periods up to seven days are the ester type fusarinine compounds. During longer periods of incubation, the fusarinine compounds completely disappear from the culture medium and are replaced by a new siderochrome. The new compound has been isolated, purified, and its structure determined. It is a cyclic hexapeptide containing one residue of L-alanine, two residues of glycine and three residues of delta-N-hydroxyornithine. The hydroxylamino groups of the ornithine residues are acylated with 3 mol of malonic acid to form a negatively charged ferrichrome type chelate. The circular dichroism spectrum indicates that the stereochemistry about the iron is lambda-cis. This compounds, which we name malonichrome, is not an efficient iron donor to F. roseum nor does it show growth factor activity towards Arthrobacter flavescens.

Uptake and translocation of iron from ferrated rhodotorulic acid in tomato

Abstract Micro‐organisms may develop an iron‐deficiency stress when grown in an alkaline environment and secrete ferric‐specific chelators known as siderophores. Some of these siderophores may have stability constants which can exceed 30. This is comparable to the synethetic Fe chelate FeEDDHA. Our objective was to determine if the Fe‐efficient T3238 FER tomato and the Fe‐inefficient T3238 fer tomato could use iron supplied as the siderophore ferrated‐rhodotorulic acid. After these two tomato cultivars were grown with adequate nutrition to obtain plants large enough for experimental testing, they were grown without iron until Fe‐deficiency‐stress symptoms developed and then iron was supplied as ferrated‐rhodoturulic acid. Iron efficient T3238 FER tomato utilized iron supplied as the siderophore and greened whereas, the Fe‐inefficient T3238 fer tomato plants were chlorotic because they could not use the iron in the siderophore. This study demonstrated that some higher plants subjected to various degrees of...

The biological activity of some siderochrome derivatives.

Abstract Semisynthetic derivatives of natural trihydroxamic acid iron chelates, or siderochromes, have been prepared and tested for biological activity. The activity of these compounds as growth factors for Arthrobacter JG-9 or as antagonists to the siderochrome antibiotic, albomycin, is relatively unaffected by structural alteration. However, their ability to function as ferric ionophores for the fungus, Ustilago sphaerogena , is very sensitive to minor structural variations. Branching at the β-position of the hydroxamate acyl function leads to loss of all biological activity.

Role of two siderophores in Ustilago sphaerogena: Regulation of biosynthesis and uptake mechanisms

Under iron-deficient conditions the smut fungus Ustilago sphaerogena produces two kinds of siderophores, ferrichrome and ferrichrome A. Regulation of ligand biosyntheses and uptake mechanisms of the iron chelates were studied to determine the role of each chelate in U. sphaerogena. The biosynthesis of each ligand was differentially regulated. Ferrichrome A, the more effective chelate, was preferentially synthesized under more extreme conditions of iron stress, but completely repressed when the cell was supplied with sufficient iron. In contrast, biosynthesis of ferrichrome was strongly but not completely repressed by iron. The mechanism of repression was examined using a newly developed in vivo synthesis assay. Chromium and gallium-containing siderophore analogs had no effect on siderophore ligand biosynthesis. Iron, added as siderophores, resulted in increased oxygen uptake and amino acid transport, which was soon followed by decreased ligand biosynthesis, suggesting that regulation may be indirect and related to oxidative metabolism. Uptake experiments were used to rule out a ligand-exchange mechanism for ferrichrome A-iron transport. The data suggest that ferrichrome A-iron is taken up at a specific site that results in a rapid distribution of iron inside the cell.

Synthetic ferrichrome analogues with growth promotion activity for Arthrobacterflavescens

Two families of trihydroxamic acid analogues of ferrichrome were chemically synthesized and tested for biological activity with Arthrobacter flavescens. Compounds using a tertiary amine as anchor showed little activity. Several compounds using tetrahedral carbon as anchor showed activity approaching or equalling that of the natural siderophore, ferrichrome. The biological activity is discussed in relation to physical and chemical properties of the analogues.

Retrohydroxamate ferrichrome, a biomimetic analogue of ferrichrome

A new synthetic analogue of ferrichrome, retrohydroxamate ferrichrome, has been examined for biological activity. Although spectroscopic evidence indicates that the analogue is a weaker Fe(III) chelator than ferrichrome, retrohydroxamate ferrichrome is indistinguishable from ferrichrome in its growth factor activity for Arthrobacter flavescens, and in its potency in antagonizing the antibiotic activity of albomyhcin against Bacillus subtilis. It is as active as ferrichrome as a siderophore for the fungus, Ustaligo sphaerogena. In contrast, desmethylretrohydroxamate ferrichrome shows no significant biological activity.

A convenient assay for siderochrome hydrolytic enzymes

Abstract Conditions are described under which ethylenediaminetetraacetate (EDTA) rapidly dissociates ferric ion from chelation with monohydroxamic acids and dihydroxamic acids, but under which the metal is not dissociated from natural trihydroxamic acids (siderochromes). Based upon this observation, enzymes which hydrolyze siderochromes to monohydroxamic acid subunits can be conveniently assayed spectrophotometrically. The characteristic absorption at 425–440 nm of the siderochrome decreases linearly during hydrolysis. The application of this assay to an enzyme isolated from an unidentified species of penicillium is described.

A model for carrier-mediated iron transport

Abstract A model transport system is described in which iron can be quantitatively transported from an outside compartment to an inside compartment separated by an organic phase. Transport is dependent upon the presence of a ferric ionophore, ferrichrome or ferrichrome A. The metal is reduced to the ferrous state by ascorbic acid in the inner compartment and trapped by the water-soluble ferrous chelator, ferrozine. The iron-trapping mechanism provides a thermodynamic drive analogous to trapping by heme synthesis in vivo. Conditions are described which allow ferrichrome, but not ferrichrome A, to act as an ionophore. It is shown that transfer of iron from ferrichrome A to deferriferrichrome is kinetically possible, suggesting a role for ferrichrome A in vivo.

Reaction of cyanide with hydroxamic acid iron complexes to distinguish trihydroxamates from simple monohydroxamates

At high pH primary hydroxamic acid-iron complexes react rapidly with potassium cyanide to yield a deep blue iron complex. Secondary, or N-substituted, monohydroxamic acid-iron complexes also react with loss of the red color typical of these complexes but with no formation of the blue product. Under the same conditions, trihydroxamates do not react at a significant rate. The blue complex is similar in many respects to the previously described Fe(CN)5NO3- but is noteworthy in its stability to oxidation and extremely high pH. Lack of formation of the blue complex with secondary hydroxamates is attributed to the absence of inorganic hydroxylamine so that the nitrosyl group cannot be formed. Lack of reactivity of siderophore trihydroxamates is due to the much greater stability of their iron complexes. The reaction is a simple, convenient method of distinguishing primary, secondary, and siderophore trihydroxamic acids.