Manganese
What function does it perform, in critical metabolic events in human biology?
Manganese acts as a co-factor to nearly all classes of enzymes such as hydrolases (phosphohydrolase), transferases (phosphotransferase), ligases, lyases, oxido-reductases, kinases and decarboxylase. It also helps in the synthesis of mucopolysaccharides, proteoglycans and glycoproteins. It can also mediate reactions as a metalloenzyme (Medeiros & Wildman, 2015; Gropper & Smith, 2013). While manganese can be replaced by magnesium in some of the catalytic reactions, two reactions in the synthesis of connective tissue pathway, namely, the activation of xylosyl transferase and glycosyl transferase or galactosyl transferase, are specifically manganese–dependent. These reactions are crucial for the synthesis of proteoglycans, the structural components of cartilages and bones.
Manganese helps in the formation of urea by binding to the enzyme Arginase. The enzyme phosphoenolpyruvate carboxykinase is activated by manganese to perform a very important step during gluconeogenesis. In the mitochondria, Mn3+ - dependent superoxide dismutase (Mn-SOD) protects the organelle from the damaging effects of superoxide (Medeiros & Wildman, 2015; Gropper & Smith, 2013).
What is the structure of Manganese?
Manganese is a transition element and atomic number 25. It is abundantly available in the nature, but is found sparingly in the human tissue (Medeiros & Wildman, 2015; Gropper & Smith, 2013). It can exist as Mn-3 to Mn+7. The biochemically important valence is Mn2+, which acts as the cofactor to the enzymes (Gibney et al., 2009). The ionic radius of Mn2+ is 0.8 Å, which is between that of calcium (0.99 Å) and magnesium (0.66 Å), the two ions that are often replace manganese in biochemical reactions for catalysis (Selinus et al., 2013).
How does it chemical structure work for individual biochemical events?
Manganese is redox active and has a standard reduction potential of +1.51 V. The metal ion helps in the enzymatic reactions by bringing about reversible oxidation states of the ion using oxidation-reduction reactions. For example, during the citric acid cycle, isocitrate is converted to α-ketoglutarate via the formation of an unstable intermediate called oxalosuccinate. Binding of the Mn2+ ion to the reduced oxygen on the oxalosuccinate results in the stabilization of the structure by the release of carbon dioxide and the addition of an H+ ion (Voet, Voet & Pratt, 2013).
What are the consequences of manganese dietary deficiency?
Reduced absorption of manganese can occur in food that are rich in iron, calcium and phosphorous (Soetan, Olaiya & Oyewole, 2010). In humans, manganese deficiency is rare when compared to animals and does not occur until the mineral is specifically avoided. Studies showed that a daily intake of 0.35 mg or less of manganese resulted in manganese deficiency. Symptoms of deficiency include vomiting, decreased growth of nails, hair, bone and skeletal structures, decrease in the levels of clotting factors and lipid metabolism (Medeiros & Wildman, 2015; Gropper & Smith, 2013).
How can manganese deficiency be diagnosed?
Where do humans suffer from severe deficiency?
The only way a person could be severely deficient of manganese would be if the metal was deliberately avoided in the diet (Gropper & Smith, 2013). A diet solely based on meat, corn and high iron could result in severe manganese deficiency (Soetan et al., 2010).
What is the daily requirement of this mineral for humans?
Recommended intake for an adult male is 2.3 mg/day and for an adult female is 1.8 mg/day (Medeiros & Wildman, 2015; Gropper & Smith, 2013). During pregnancy, the recommended intake is 2 mg/day and during lactation is 2.6 mg/day. The human tissue consists of 12 to 20 mg of manganese (Gropper & Smith, 2013). Manganese is highly concentrated in the mitochondria, nucleus, bone, liver, pancreas, kidneys, lactating mammary glands and pituitary glands. The levels of manganese found in bone and liver are 3.5 mg/kg and 2 mg/kg, respectively (Medeiros & Wildman, 2015; Gropper & Smith, 2013).
What are good dietary sources of manganese?
Whole grains, leafy vegetables, nuts and dry fruits are common sources of manganese. A cup of wheat bran provides about 1.7 mg of manganese. Dried nuts such hazelnut, cashew, almond and pecan contain 0.5 to 1.8 mg manganese per ounce. Beans such as kidney beans and navy beans consists of 0.76 to 0.96 mg in one cup. Half a cup of spinach, turnip greens and collard greens provide around 0.8 to 1.7 mg of manganese. Among fruits, pineapple is manganese-rich and can contribute 2.3 mg per cup (Medeiros & Wildman, 2015; Gropper & Smith, 2013).
What harm (if any) results from consuming very large amounts of manganese?
Oral, air and parenteral manganese could lead to toxicity, although such an occurrence is rare (Medeiros & Wildman, 2015; Gropper & Smith, 2013). Individuals with liver failure are at higher risk of manganese toxicity because under normal conditions manganese is excreted quickly from the body by the liver through the bile to maintain homeostasis (Medeiros & Wildman, 2015; Gropper & Smith, 2013).
During toxicity, manganese has a tendency to accumulate in the brain, which could cause impaired cognitive functions. This is the reason why miners working in manganese mines who have been exposed to high levels of manganese tend to exhibit symptoms that resemble Parkinson’s disease (Medeiros & Wildman, 2015). Some of the symptoms of manganese toxicity are chronic cough, bronchitis, reduce reflexes, reduced cognition and loss of memory (Gropper & Smith, 2013).
Would Americans benefit from more (or less) in their diet?
A typical American diet provides 3 to 9 mg/day of manganese. Since the daily requirement is between 1.8 and 2.6 considering various age groups and sects of people, the current diet seems sufficient and requires no change (Gropper & Smith, 2013).
Iron
What function does it perform, in critical metabolic events in human biology?
Iron has a critical function in the transport of oxygen in the form of hemoglobin, energy production via the electron transport chain that involves cytochrome b and c using iron’s oxidation reactions, in spinal cord and white matter myelination, and as a cofactor for enzymes involved in neurotransmission (Soetan et al., 2010).
Biochemically, apart from being a major component of the porphyrin ring of heme, iron is also present as oxygen bridge in ribonucleotide reductase, as elemental iron and as part of proteins such as oxido-reductase, myoglobin, peroxidases catalases and cytochromes (Medeiros & Wildman, 2015; Gropper & Smith, 2013).
What is the structure of iron?
Iron is a transition metal with atomic number 26 and is the fourth most abundant element on Earth (Selinus et al., 2013). Common oxidation states of iron range between -2 to +6. In biological systems, the most common valences of iron are Fe2+ (ferrous), Fe3+ (ferric) and Fe4+ (ferryl) (Gibney et al., 2009; Selinus et al., 2013). The ferrous form is more soluble than the ferric form (Soetan et al., 2010). Iron has the ability to bind to biological ligands such as oxygen, nitrogen and sulfur due to its empty d orbitals. Ferric is a hard acid while ferrous is in between hard and soft acid (Selinus et al., 2013).
How does it chemical structure work for individual biochemical events?
The inherent differences between the two forms of iron drive the various biological functions such as the oxygen carrying ability of hemoglobin. When Fe(II) atom is exposed to oxygen, it is oxidized to Fe(III) atom, which makes the hemoglobin molecule undergo structural change and reduces its affinity towards oxygen.
The redox nature of iron helps in the electron transport chain, where the Fe(II) and Fe(III) donate and remove electrons within the cytochromes to facilitate the transport. Therefore, it can be said that iron’s reactivity can be adjusted to suit the ligand because of its unique electronic spin, redox potential and oxidation state (Selinus et al., 2013).
What are the consequences of dietary deficiency?
Iron deficiency is termed as anemia and is characterized by plasma iron levels of 40μg or less per deciliter or less than 12g/dL of hemoglobin. Anemia reduces the blood’s ability to carry oxygen, which results in short attention span, lethargy, impaired learning capability, behavioral disturbances, paleness of skin and reduction in overall productivity. Other consequences of iron deficiency include altered neurotransmitter metabolism and protein synthesis (Medeiros & Wildman, 2015; Gropper & Smith, 2013; Soetan et al., 2010).
How can deficiency be diagnosed?
A standard test for hemoglobin levels is widely used for determining iron deficiency. Hematocrit concentrations with below 37% for women and below 40% for men indicates anemia. Additionally, tests for mean corpuscular volume, (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) are also performed to assess iron status in the body (Gropper & Smith, 2013).
Where do humans suffer from severe deficiency?
Individuals who follow a solely plant-based diet is at higher risk of developing iron deficiency, since iron from plants are not easily absorbed and are typically have less bioavailability when compared to animal-based iron sources (Gropper & Smith, 2013). Infants under the age of 6 months are at risk of anemia since their diet is milk-based and low in iron. Adolescents, menstruating women and pregnant women are another risk population who could develop iron deficiency owing to high body demand, loss of iron and high fetal demand, respectively (Gropper & Smith, 2013).
What is the daily requirement of iron in humans?
The human body contains 2-4 g of iron. Adult males require 6 mg/day and are recommended 8 mg/day. Women under the menstruating and childbearing age require 8.1 mg/day and are recommended 18 mg/day. Post-menopausal women require 5 mg/day and are recommended 8 mg/day. Pregnant women are recommended 27 mg/day and lactating females are recommended 9 mg/day (Gropper & Smith, 2013).
What are good dietary sources?
Sources high in heme iron are the best sources of iron. Sources such as fish, meat and poultry contain 50 to 60% of heme iron and are absorbed directly by the body. Oysters and clams provide 8 – 12 mg iron/3 ounces. Beefs contains 2 mg iron/3 ounces and chicken contains 1 mg iron/3 ounces.
Plant-based sources contain non-heme iron, which is poorly absorbed by the body. Plant-based sources include spinach and collard greens (3 mg of iron per half a cup), beans (1.8 to 2.2 mg iron/half cup), dried fruits and enriched cereals (Medeiros & Wildman, 2015; Gropper & Smith, 2013)
What harm (if any) results from consuming very large amounts?
Humans can tolerate iron overload of up to 45 mg. Iron toxicity causes damage to the liver and gastrointestinal tract. Iron toxicity could be acute toxicity or chronic in nature. Acute toxicity could occur from over consumption of iron in the form of supplement pills, which is fatal to children below 6 years of age. Symptoms include abdominal pain, vomiting, melena and even coma.
Within the body, the iron acts as a free radical and produces toxins that causes acidosis, hyperglycemia and results in liver damage and bleeding (Selinus et al., 2013). Chronic iron toxicity could be a result of transfusion, where the individual suffers from a hereditary or chronic anemia. Chronic iron toxicity can cause heart failure, diabetes and hypothyroidism (Selinus et al., 2013).
Would Americans benefit from more (or less) in their diet?
A typical American diet provides 5 to 7 mg iron/1000 kCal, which provides adequate iron for adult male and post-menopausal women. However, individuals with higher iron demand would have to take effort to add more iron-rich food in their daily diet (Medeiros & Wildman, 2015; Gropper & Smith, 2013).
Sulfur
What function does it perform, in critical metabolic events in human biology?
In metabolic event, sulfur does not act alone as a mediator or cofactor but is associated structurally with metabolites such as glutathione, vitamins such as thiamin and biotin and amino acids such as methionine, cysteine and taurine (Gropper & Smith, 2013; Nimni, Han & Cordoba, 2007). Plasma thiols are pro-oxidant or antioxidants. The sulfur-containing amino acids such as methionine, cysteine, and taurine are provided by diet and they in turn provide the sulfur that is essential for metabolic pathways within the human system (Parcell, 2002). Sulfur is abundant in breast milk with the colostrum containing three times more sulfur. In the human body, sulfur constitutes the third most abundant mineral (Parcell, 2002).
What is the structure of sulfur?
Sulfur is a non-metallic mineral with the atomic number 16. The chemical structure of sulfur allows many states of oxidation such as sulfide (SO3 2-) and sulfate (SO4 2-) (Parcell, 2002). The ability of sulfur to form transient covalent bonds through the disulfide bonds is one of the major mechanisms by which sulfur mediates biochemical processes. Sulfur has versatile roles in lower oxidation states while higher oxidation states help with detoxification and sulfation (Selinus et al., 2013).
How does it chemical structure work for individual biochemical events?
In humans, the amino acid cysteine provides the elemental sulfur required for carrying out biochemical processes. The covalent bond of sulfur’s disulfide bond helps in protein folding, enzyme catalysis, protonation of sulfur in the iron-sulfur protein [3Fe–4S]0,2- and redox regulation. Sulfur combines with ligands via its μ3 sulfide bond in the Fe-S clusters and helps in the catalysis of homolytic reactions such as anaerobic ribonucleotide reductase, biotin synthase and lysine amino mutase (Selinus et al., 2013).
What are the consequences of dietary deficiency?
There are no studies on the consequence of elemental sulfur deficiency. However, knowing that sulfur is derived from essential amino acids such as cysteine and methionine, a dietary deficiency of these amino acids could lead to depletion of stored reserves of sulfur in the form of glutathione, the in-house antioxidant. Reduction in levels of glutathione would lead to tissue damage arising from reactive oxygen species (Parcell, 2002).
Deficiency of sulfur-containing amino acid has been associated with reduced growth (Parcell, 2002). Similarly, a deficiency of sulfur containing vitamins such as biotin and thiamin is associated with lethargy, pain, general weakness and neuropathy (Gropper & Smith, 2013).
How can deficiency be diagnosed?
There are no methods to detect sulfur deficiency, although a deficiency test for sulfur containing amino acids, thiamin and biotin by testing blood plasma levels might be effective (Gropper & Smith, 2013).
Where do humans suffer from severe deficiency?
As mentioned earlier, there are no reported cases of sulfur deficiency in humans (Gropper & Smith, 2013). However, individuals on a low protein diet and consuming plants grown in sulfur-depleted soil might be at risk of sulfur-deficiency (Komarnisky et al., 2003).
What is the daily requirement of this mineral for humans?
The recommended allowance for sulfur has not been established, although, the recommended intake of methionine and cysteine together is suggested as 14 mg/Kg/day for an adult (Parcell, 2002). Recommended levels of thiamin are 1.2mg/day for adult men and 1.1 mg/day for women. The requirements are 1 mg/day for men and 0.9 mg/day for women. For biotin, 30 μg per day has been recommended for adults (Gropper & Smith, 2013).
What are good dietary sources?
As mentioned earlier, the body’s sulfur needs are met by the sulfur containing amino acids, cysteine and methionine. Among these two sulfur amino acids, cysteine can be derived from methionine and is used for further biological process; however, cysteine cannot be converted to methionine. This makes diet the only way to obtain methionine. Foods rich in these amino acids are beans, legumes, meat, poultry and fish.
The amount of sulfur-rich proteins are high in animals when compared to plants. On the contrary, vegetable such as onion, cabbage, broccoli and garlic provide glutathione, an important source of sulfur within the human body. Animal protein contributes to less than 25% of the body’s glutathione needs (Parcell, 2002).
What harm (if any) results from consuming very large amounts of sulfur?
Currently, there are no studies on sulfur toxicity pertaining to human beings. However, in large quantities sulfur has been found to be toxic to animals such as cow and rabbits (Komarnisky et al., 2003).
Would Americans benefit from more (or less) in their diet?
A typical American diet of animal proteins, eggs, greens, fruits and vegetables provides 3.6 g of sulfur-containing amino acids, which is sufficient as per the recommendations stated in previous sections (Ingenbleek, 2006). Therefore, no changes are required in the current diet.
References
Gibney, M. J., Vorster, H. H., & Kok, F. J. (Eds.). (2009). Introduction to human nutrition (2nd ed.). West Sussex, England: Wiley-Blackwell.
Gropper, S. A., & Smith, J. L. (2013). Advanced nutrition and human metabolism (6th ed.). Boston, MA: Cengage Learning.
Ingenbleek, Y. (2006). The nutritional relationship linking sulfur to nitrogen in living organisms. The Journal of nutrition, 136(6), 1641S-1651S.
Komarnisky, L. A., Christopherson, R. J., & Basu, T. K. (2003). Sulfur: its clinical and toxicologic aspects. Nutrition, 19(1), 54-61.
Medeiros, D. M., & Wildman, R. E. (2015). Advanced human nutrition (3rd ed.). Sudbury, MA: Jones & Bartlett Learning.
Nimni, M. E., Han, B., & Cordoba, F. (2007). Are we getting enough sulfur in our diet?. Nutrition & Metabolism, 4(1), 1.
Parcell, S. (2002). Sulfur in human nutrition and applications in medicine. Alternative Medicine Review, 7(1), 22-44.
Selinus, O., Centeno, J. A., Finkelman, R. B., Fuge, R., Lindh, U., & Smedley, P. (Eds.). (2013). Essentials of medical geology (p. 820). New York, NY, USA: Springer.
Soetan, K. O., Olaiya, C. O., & Oyewole, O. E. (2010). The importance of mineral elements for humans, domestic animals and plants: A review. African Journal of Food Science, 4(5), 200-222.
Voet, D., Voet, J. G. P., Charlotte, W., Judith, G. V., & Charlotte, W. P. (2013). Fundamentals of biochemistry: life at the molecular level (No. 577.1 VOE).
