Haemoglobin biosynthesis

Pyridoxine is involved as a co-factor coenzyme in about 100 enzyme systems. Thus, in addition to the reactions mentioned above, it is required for glycogen phosphoryl-ase, which catalyses the release of glucose from stored glycogen, haemoglobin biosynthesis, the generation of glucose from amino acids (gluconeogenesis), the biosynthesis of niacin from tryptophan and nucleic add biosynthesis. 

In 1992 the X-ray crystal structure of porphobilinogen deaminase was solved, an enzyme that is involved with the biosynthesis of a linear tetrapyrrole precursor to protoporphyrin IX, found in haemoglobin... 

Iron, zinc and copper are the most prevalent metals in the body, and perhaps not surprisingly are the most common supplementation treatments. Of these, iron dehciency is the most commonly observed and there are over 40 preparations of iron used therapeutically (including iron(II) sulfate iron(ll) fumarate iron(II) gluconate and iron(ll) succinate), compared with 3 for zinc (including zinc(II) sulfate). Notably, as folate plays a vital role as a cofactor in the biosynthesis of haeme (for haemoglobin), sometimes it is necessary to co-administer iron with folic acid in so-called compound oral iron preparations . 

The catabolism of haemoglobin yields haem, which is subsequently converted to bilirubin in a two-step process that takes place in the hepatocyte. First, the microsomal enzyme haem oxygenase cleaves the porphyrin ring of haem, generating biliverdin in an energy-utilising reaction. Following this, biliverdin is converted to bilirubin by the cytosolic enzyme biliverdin reductase. As the liver is the active site for biosynthesis of porphyrin and haem, deficiencies in some enzymes of the porphyrin pathway may lead to insufficient haem production and an increase in porphyrin levels, which causes acute porphyria attacks. 

The best documented effects of lead on blood are its interference with the biosynthesis of haem, which is essential for the production of haemoglobin (the red oxygen-carrying pigment in red blood cells). The two most important points of interference are the formation of the enzyme 6-aminolaevulinic acid dehydratase (6-ALAD) and the insertion of iron into protoporphyrin [6]. 

The resorption of hexavalent chromium compounds is 3-5 times higher than resorption of trivalent chromium compounds. In blood, hexavalent chromium enters into blood cells and erythrocytes more easily than trivalent chromium and binds to haemoglobin. Trivalent chromium is resorbed in the blood plasma bound to a-globuhn and transferrin. Transferrin provides chromium transportation to the tissues. In some target tissues, chromium from transferrin binds to apochromoduhn with the formation of chromodulin. In the cells, about 50% of chromium is contained in the nucleus and about 20% in the cytoplasm. Chromium is excreted from the body mainly in the urine. Excessive intake of chromium by experimental animals or chromium intoxication also leads to excretion of chromodulin in the urine. Biosynthesis of this metaUopeptide thus participates in the detoxification of chromium. 

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