Reduction of exogenous FMN by isolated rat liver mitochondria. Significance to the mobilization of iron from ferritin

Impact of COVID-19 on male urogenital health: Success of vaccines

Throughout 2021, the scientific and medical communities were concentrated on dealing with the acute morbidity and mortality induced by the COVID-19 pandemic due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We reviewed the present data for adverse effects of COVID-19 on the different parts of the male urogenital system during the dynamic situation of the COVID-19 pandemic. With the approval of COVID-19 vaccinations, there is a ray of hope at the end of this dark tunnel and a chance to look ahead for the management of long-term consequences in males with urogenital illness. A multidisciplinary investigation of these cases could provide information for establishing and optimizing treatment protocols.

Riboflavin deficiency in the rat: effects on iron utilization and loss

Iron absorption and daily loss of Fe were measured in riboflavin-deficient (B2-) Norwegian hooded rats and controls (B2+). Animals were fed on a test meal extrinsically labelled with 59Fe and whole-body radioactivity measured for 15 d. Riboflavin deficiency led to a reduction in the percentage of the 59Fe dose absorbed and an increased rate of 59Fe loss. All post-absorption 59Fe loss could be accounted for by faecal 59Fe, confirming that the loss was gastrointestinal. Fe concentrations and 59Fe as a percentage of retained whole-body 59Fe were higher in the small intestine of riboflavin-deficient animals than their controls, 14 d after the test meal. A separate experiment demonstrated that riboflavin deficiency was associated with a significant proliferative response of the duodenal crypts of the small intestine. These observations may explain the enhanced Fe loss in riboflavin deficiency.

The effect of riboflavin deficiency in rats on the absorption and distribution of iron

1. Riboflavin may play a part in the transport of iron across the gastrointestinal mucosa. Fe absorption was measured in the rat by monitoring whole-body retention of a dose of 59Fe using a small-animal gamma-counter. 2. Female Norwegian Hooded rats were fed on a diet deficient in riboflavin (B2-) from 5 weeks of age. Control animals, fed on a complete diet (B2+), were weight-matched to rats fed on the B2- diet. After 7 weeks all rats were fed on a test meal extrinsically labelled with 59Fe and whole-body radioactivity measured for 15 d. 3. Riboflavin deficiency was associated with a reduction in the percentage of the dose absorbed and an increase in the rate of loss of Fe post absorption. 4. A smaller percentage of the absorbed dose was present in the livers of the riboflavin-deficient animals.

Superoxide ion as a primary reductant in ascorbate-mediated ferritin iron release

The mechanism of ascorbate-promoted ferritin iron reduction under aerobic conditions was studied. The initial rate of ferritin iron release was determined by spectrophotometric measurement of the Fe(ferrozine)3(2+) complex which absorbs at 562 nm. Variation of the initial ferrozine concentration had no influence on the rate of iron release suggesting that ferrozine does not participate in the rate-determining step. Experimental measurements of the initial rate of iron release as a function of ascorbate concentration resulted in saturation kinetics with Vmax = 2.0 X 10(-7) M.min-1 and KM = 1.3 X 10(-3) M. The effect of pH was quite pronounced with a maximal rate of iron release at pH 7.0. Stoichiometric measurements on the reaction mixture, with added catalase, resulted in a ratio of 2 Fe(II) released per ascorbate. Ascorbate-mediated iron release was inhibited 85% by superoxide dismutase, but 0% inhibition was noted with aposuperoxide dismutase. It is proposed that superoxide ion, generated during the iron-promoted oxidation of ascorbate, acts as a reductant of ferritin iron. A mechanism of ferritin iron release consistent with these experimental observations is discussed.

A comparative study on iron sources for mitochondrial haem synthesis including ferritin and models of transit pool species

The rates of reaction of various exogenic iron(III) complexes with deuteroporphyrin IX in isolated mitochondria to form deuterohaem were measured. Ferritin was shown to supply iron readily for haem synthesis if the ferritin iron was reductively mobilised by the mitochondrial respiratory chain with succinate as substrate and FMN as mediator. In contrast, polynuclear complexes of iron(III) were able to form deuterohaem without added FMN. Rates of haem formation are about five times higher for the lowest polynuclear units than for ferritin. Sorbitol, gluconate, and bovine serum albumin were used as scavengers for polynuclear complexes with restricted size. Strong chelators of iron(II) compete favourably for deuterohaem formation, which supports the multistep mechanism for haem formation suggested by a priori arguments. Rates of deuterohaem formation were measured in homologous and heterologous systems of ferritins and mitochondria. Slightly differing rates of haem formation were shown to originate in different rates of iron mobilisation from the ferritins. The lack of species specificity in the interaction of ferritin with mitochondria also shows up in the linear dependence of ferritin binding on its bulk concentration as measured using 3H-labeled ferritin. Rates of haem formation are virtually the same in mitoplasts and mitochondria which indicates insignificant influences of the outer membrane. The hypothesis of low polynuclears as major components of the intracellular transit iron pool implies that both ferritin and transit iron pool species are largely equivalent sources of iron for mitochondrial haem synthesis.

Role of metals in oxygen radical reactions

Partially-reduced forms of dioxygen or "oxy-radicals" (superoxide, O2-/HO2; hydrogen peroxide, H2O2; hydroxyl radical X OH) and oxidants of comparable reactivity are implicated in an increasing number of physiological, toxicological, and pathological states. Transition metal catalysis is recognized as being integral to the generation and the reactions of these activated oxygen species. Factors such as pH and chelation govern the reactivity of the transition metals with dioxygen and "oxy-radicals" and therefore influence the apparent mechanisms by which oxidative damage to phospholipids, DNA, and other biomolecules is initiated. In biological systems the concentrations of redox-active transition metals capable of catalyzing these reactions appears to be relatively low. However, under certain conditions metal storage and transport proteins (ferritin, transferrin, ceruloplasmin, etc.) may furnish additional redox active metals.

Ferritin in bean leaves with constant and changing iron status

Normal green leaves contain low levels of ferritin which stores 5 to 10% of the total iron (approximately 350 iron atoms/molecule). Chlorotic leaves do not have measurable amounts of ferritin, whereas iron-loaded leaves contain high levels of well-filled ferritin (1,500 to 2,500 iron atoms/molecule). The role of ferritin during a transient iron surplus in leaves was investigated. It is suggested that a short-term overdose of iron transported into the leaf is largely stored in or near the vessels in such a form that it can be quickly mobilized for export. Iron that reaches the mesophyll cells in an overdose situation is stored in ferritin and, when released, is most likely used for the leaf cells themselves and not for export.

Relevance of ferritin-binding sites on isolated mitochondria to the mobilization of iron from ferritin

Iron can be released from ferritin and utilized by isolated rat liver mitochondria for the synthesis of heme. Mobilization of iron from ferritin is initiated by the binding of ferritin to the mitochondria in an manner compatible with binding sites or receptors for ferritin on the mitochondria. The binding completes rapidly, it is independent of temperature, saturable, reversible and enhanced by K+ and Mg2+. The amount of ferritin binding sites is approx. 0.8 pmol/mg mitochondrial protein, and the affinity constant is 6.4 . 10(6)M-1. The binding kinetics correlate well with the functional features of the ferritin-mitochondrial interaction: i.e. mobilization of iron from ferritin followed by insertion of the iron into heme. The results support the concept of ferritin as a possible donor of iron to the mitochondria.