Engineering Chemistry S Datta

26
Role of Metals in Biology
Metal ions are required for many critical functions in biological systems. The normal
concentration range for each metal in biological system is narrow, with both deficiencies and
excesses causing pathological changes. The elements
required in human nutrition can be grouped into
bulk and trace groups. The bulk elements are
required in excess of 100 mg/day, whereas the trace
elements are required in amounts not greater than
a few mg/day. The transition metals for which
biological storage and transport are significant are
in order of decreasing abundance: iron, zinc, copper,
molybdenum, cobalt, chromium, vanadium and
nickel. The form of the metals is always ionic, but
the oxidation states can vary on biological needs. The
metals are generally found either bound directly to
proteins or in cofactors such as porphyrins or
cobalamins. Proteins with which transition metals
and zinc are most commonly associated catalyze the
intra and intermolecular rearrangement of electrons.
In this respect, the redox properties of the metals
Elements required in Human
nutrition
Bulk elements
• Calcium
• Magnesium
• Sodium
• Potassium
Trace elements
• Copper
• Iron
• Manganese
• Molybdenum
• Selenium
• Zinc
are important, in others metals appear to contribute to the structure of the active state. An
essential metal ion may function as a potent electron-withdrawing agent at some point in the
catalytic function of enzymes which require metal ions for their activities and are called
metalloenzymes (Table 26.1).
Table 26.1: Some Enzymes Containing or Requiring Essential Inorganic Elements as Cofactors
Fe 2+ or Fe 3+
Cu 2+
Zn 2+
Mg 2+
Mn 2+
K +
Ni 2+
Mo
Se
Cytochrome oxidase
Catalase
Peroxidase
Cytochrome oxidase
DNA polymerase
Carbonic anhydrase
Alcohol dehydrogenase
Hexokinase
Glucose 6-phosphatase
Arginase
Pyruvate kinase
(also requires Mg 2+ )
Urease
Nitrate reductase
Glutathione peroxidase
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