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Biomedical subjects

J B Neilands

Publications and source records attributed to J B Neilands.

101 records · Page 6Linked to original sources
PubMed1970

Rhodotorulic acid from species of Leucosporidium, Rhodosporidium, Rhodotorula, Sporidiobolus, and Sporobolomyces, and a new alanine-containing ferrichrome from Cryptococcus melibiosum.

An examination of 142 strains within 19 genera of yeasts and yeastlike organisms for formation of hydroxamic acids in low-iron culture showed production of hydroxamates by two unclassified strains and by 52 strains among the genera Aessosporon (3 of 3 strains), Cryptococcus (1 of 43), Leucosporidium (3 of 11), Rhodosporidium (4 of 4), Rhodotorula (27 of 39), Sporidiobolus (2 of 2), and Sporobolomyces (12 of 13). Crystalline rhodotorulic acid was isolated in amounts sufficient to account for most or all of the measured hydroxamate in culture supernatants of 16 strains representative of the five last-mentioned hydroxamate-producing genera. A new alanine-containing ferrichrome was isolated from one strain of Cryptococcus melibiosum. Rhodotorulic acid was a major metabolic product of many of the positive strains when grown in low-iron media, and iron was shown to repress its synthesis and excretion into the culture medium. The taxonomic significance of production of hydroxamic acids is described in connection with the position of these yeast species in the subclass Heterobasidiomycetidae.

Alanine↗
PubMed1970

Iron transport in Salmonella typhimurium: mutants blocked in the biosynthesis of enterobactin.

A number of mutants of Salmonella typhimurium were isolated which are blocked in the biosynthesis of enterobactin, an iron chelator that is secreted by the wild-type bacteria when they are grown on low iron media. One class of these enb mutants accumulates the enterobactin precursor 2,3-dihydroxybenzoic acid, and another class does not accumulate any detectable catechol precursor. The enb mutants grow very well on a glucose-mineral salts medium. Addition of citrate, itself an iron chelator, to the medium drastically inhibits growth unless the medium is supplemented with enterobactin or iron salts. Citrate inhibits iron uptake from the medium by enb mutants; enterobactin counteracts this inhibition and also, by itself, increases iron uptake. Thus, the apparent function of enterobactin is to promote the absorption of iron from the medium by the bacteria. Transduction experiments showed that the genes for enterobactin biosynthesis are closely linked on the S. typhimurium chromosome. It is suggested that they form an operon which is repressed by the presence of iron. S. typhimurium can utilize the iron chelate ferrichrome. (Deferriferrichrome is a cyclic hexapeptide that is produced by some fungi but not by S. typhimurium.) The enb mutants use ferrichrome as an effective growth factor.

Benzoates↗
PubMed1967

Hydroxamic acids in nature.

The hydroxamic acid bond occurs in products from fungi, yeast, bacteria, and plants. The -CON(OH)-bond arises by oxidation of a free or bound amino group in a unit structure which is often closely related to conventional amino acids. Products are known with one, two, or three hydroxamic acid groups per molecule. The chemistry of the ferrichrome type compounds, which are ferric trihydroxamate-containing peptides, has been worked out in detail and includes a complete crystallographic analysis of the ferrichrome A molecule. The trihydroxamates form potent complexes with ferric ion, called siderochromes, and these are believed to play a role in the metabolism of the metal ion in microorganisms. The actual physiological activity observed ranges from that of growth factor, antibiotic, antibiotic antagonist, tumor inhibitor or cell-division factor. The precise molecular mechanism whereby these substances exert their potent beological activity remains to be elucidated.

Anti-Bacterial Agents↗
PubMedDate not supplied

Siderophores: diverse roles in microbial and human physiology.

Siderophores, defined as high affinity iron(III) ion transport agents, and their cognate membrane-bound receptor complexes, occur in the enteric bacteria Escherichia coli and Salmonella typhimurium. The total system is tightly regulated by iron repression. The transport properties of the specific siderophores enterobactin and ferrichrome (which is not made by these particular enteric bacteria) have been examined in detail. In E. coli the outer membrane receptor for ferrichrome is programmed by the tonA gene; the receptor also serves as the binding site for T1, T5, phi80, albomycin and colicin M. Similarly, in S. typhimurium phage ES18, ferrichrome and albomycin compete for the genetic equivalent of the tonA locus. The ability of ascorbic acid to protect against atherosclerosis as well as rhinovirus infection in humans may be related to the role of the vitamin in iron metabolism. Deferrisiderophores are clinically useful in the treatment of acute and chronic iron poisoning but, on the other hand, they could constitute a natural hazard by transporting actinides, such as 239Pu, through the food chain.

Arteriosclerosis↗