Anatoly Bezkorovainy

Antimicrobial Properties of Iron-Binding Proteins

The transferrins are iron-binding proteins with molecular weights of around 80,000, which interact with a maximum of two ferric atoms per each protein molecule. The best known transferrins are the serotransferrins from animal sera, lactoferrins from milk, and conalbumin from egg-white. The iron-deficient transferrins will inhibit the growth of certain bacteria and fungi by making iron unavailable for bacterial metabolism. Such activity is abolished if the transferrin is saturated with iron. Many organisms can produce small molecular-weight iron-binding compounds called siderophores that can successfully utilize the iron sequestered by the transferrins. Such organisms are very virulent. Overwhelming evidence is now available to indicate that the transferrins play an important role in mammalian host-defense mechanisms. Thus, iron injections into animals infected with virulent bacteria result in increased death rates, and parenteral iron administration to human infants predisposes them to fatal septicemia. On the other hand, in cases of systemic infection, the organism responds by lowering its total serum iron, so as to make the serotransferrin present less saturated with iron. This phenomenon is called nutritional immunity. The iron apparently moves into the storage tissues from the circulation, and furthermore, it is withheld from circulation by the reticuloendothelial system. Laboratory results in such cases indicate low total serum iron levels and high unsaturated iron-binding activity values, thus increasing the bacteriostatic effects of the serotransferrins. Increased lactoferrin levels are observed in the milks of mastitic cattle.

Inhibition of Escherichia coli by bifidobacteria

The ability of five ATCC bifidobacterial species to produce antimicrobial substances was investigated by testing the effects of spent bifidobacterial broths on the growth Escherichia coli in the thioglycollate medium. Such broths were most inhibitory if their pH was not readjusted to neutrality. When that was done, the inhibition ranged from 30 to 43%. Such inhibition of E. coli growth could be duplicated by a 3:2 aceticlactic acid mixture adjusted to neutral pH. It was concluded that no antibacterial substances other than acetic and lactic acids were produced by bifidobacterial strains used, and that the effects of these ubiquitous fermentation products, as well as pH effects, be taken into consideration before the existence of other antimicrobial factors is proposed.

Some aspects of iron uptake by rat hepatocytes in suspension.

Abstract 1. 1. Ferrous iron was taken up from rat hepatocytes by a simple diffusion process, though the cells were able to concentrate it from the medium. 2. 2. Uptake of ferric iron was apparently receptor mediated. 3. 3. Uptake of transferrin-bound iron was complex: at low iron saturation levels, it was apparently receptor mediated; at iron saturation levels of 30% and above, simple diffusion without temperature dependence was observed. 4. 4. In 1–3 above, iron appearing in the cell sap was present bound to ferritin, an intracellular transferrin, and as a small-molecular weight chelate.

Cellular iron uptake from transferrin: Is endocytosis the only mechanism?

Receptor mediated endocytosis has been proposed as the method of cellular iron uptake from transferrin (TF). However, the experimental evidence for endocytosis in every situation is found wanting. This is particularly true for the hepatocyte where an alternative mechanism of iron release at the cell surface can account for all iron uptake. It may be, that under appropriate physiological conditions (e.g. degree of iron saturation of TF) cells may take up iron by either an endocytotic or nonendocytotic mechanism.

Bifidobacterium bifidus var. Pennsylvanicus growth promoting activity of human milk casein and its derivatives

1. 1. Bifidobacterium bifidus var. Penn, growth promoting activity of human milk and compounds derived therefrom can be expressed by a reciprocal plot, from which constants representing such activity can be derived. 2. 2. Human milk casein has microbial growth-promoting activity that apparently resides in its oligosac-charide moiety. 3. 3. Three types of oligosaccharides were demonstrated in the product of β-elimination reaction on human casein, and all had microbial growth promoting activities. 4. 4. Carbohydrate-free human casein was a competitive inhibitor of microbial growth in the presence and absence of human milk. 5. 5. Bovine milk casein and its corresponding derivatives had no effect on microbial growth. 6. 6. It is concluded that the title microorganism may possess growth promoter receptors on its surface, which can reversibly combine with carbohydrate-free human casein, and that human casein may contain a number of different oligosaccharide units.

Limited cleavage of human lactoferrin with pepsin

Abstract 1. 1. Human lactoferrin in the iron-saturated form was treated with pepsin at pH 3.0, and a fragment with a single iron-binding site was isolated in a 90% pure state. 2. 2. Its mol. wt was near 33,000. 3. 3. Its N-terminal residue was alanine, and its iron-binding properties were identical to those of lactoferrin. 4. 4. The curve showing iron incorporation from lactoferrin and its fragment into reticulocytes showed a biphasic character. 5. 5. It is concluded that lactoferrin consists of two largely independent parts, which may have arisen by a gene duplication process.

Iron incorporation into isolated rat hepatocytes

Abstract Isolated rat hepatocytes incorporated ferrous iron by a simple diffusion process, whereas the incorporation of ferric iron (complexed with citrate) and transferrin-bound iron followed Michaelis-Menten kinetics. Ferrous iron was incorporated at a rate 2–3 times that of ferric citrate, and 4 times that of transferrin-bound iron. When the hepatocytes were prepared using the soybean trypsin inhibitor in the perfusion medium, the rate of transferrin-bound iron incorporation was increased 3-fold. It is concluded that rat hepatocyte membranes contain an iron-transferrin receptor, which functions as part of the mechanism for iron uptake by the liver.

Human colostral whey M-l glycoproteins and their L. bifidus var. Penn. growth promoting activities

Abstract A total of seven M-1 glycoprotein fractions were isolated from human colostrum whey and all showed L. bifidus var. Penn. growth promoting activities using well defined chemical medium. The growth promoting activity of these fractions was parallel to their total carbohydrate content. On the other hand, bovine colostrum M-1 glycoprotein had a relatively low growth promoting activity, whereas human serum orosomucoid had none.

Ferrous iron uptake byBifidobacterium breve

Bifidobacterium breve transports ferrous iron in preference to the ferric form in a saturable, concentration-dependent manner with an optimum pH of 6. Iron transport is highly temperature sensitive. Two transport systems with apparent Km’s of 86±27 and 35±20 μM (p>0.01) were distinguished, one operating at high iron concentrations, the other at low iron concentrations. Iron uptake could not be accounted for by surface binding. Uptake of iron was inhibited by iron chelators, a proton ionophore, and ATPase inhibitors, and it was stimulated by potassium ionophores. The presence of a ferri reductase in the insoluble cell fraction ofB. breve and its “spent” growth medium was demonstrated. The hypothesis is presented that iron uptake by bifidobacteria is related to the nutritional immunity phenomenon.

Protein and electrolyte changes in experimental cerebral edema.

Analysis of protein and electrolyte data in cryogenic cerebral edema in the rhesus monkey has led to the conclusion that, in the first 24 hours (h) after injury, the edamatous process is not homogenous, but compartmentalized. This involves, first of all, a division into intra- and extracellular compartments. The intracellular compartment is further divided into a compartment containing water, electrolytes, and serum proteins, and a compartment containing only excess sodium. The extracellular compartment is also subdivided into a compartment containing albumin, globulin, and electrolytes, and a compartment containing only albumin and electrolytes. Anatomically, the latter is most likely the pre-existing normal extracellular space