Nutritional Requirements 127 Table 1. Physiological functions of the principal elements J (31 Element Symbol Atomic Physiological function Constituent of cellular water C Constituent of organic cell materials Constituent of proteins, nucleic acids and coenzymes Oxygen Constituent of cellular water and electron acceptor in respiration of aerobes Important divalent cellular cation, enzymatic reactions, incl. those involving ATP; functions in binding enzymes to substrates and present in chlorophylls Phosphon P Constituent of phospholipids, 16 Constituent of cysteine, cystine, methionine and proteins CoA and cocarboxylase Chlorine Principal intracellular and extracellular anion Potassium K 19 Principal intracellular cation, cofactor for some enzymes Calcium Important cellular cation, cofactor for enzymes as proteinase Inorganic cofactor Iron Constituent of cytochromes nd other heme or non-heme proteins, cofactor for a number of Cobalt Constituent of vitamin B,2 and Copper Z1 30 Inorganic constituents of Molybdenum Mo special enzymesNutritional Requirements 127 Table 1. Physiological functions of the principal Element Symbol Atomic Physiological function Hydrogen Carbon Nitrogen oxygen Sodium Magnesium Phosphorus Sulfur Chlorine Potassium Calcium Manganese Iron Cobalt Copper zinc Molybdenum H C N 0 Na Mg P S c1 K Ca Mn Fe co cu Zn Mo 1 6 7 8 11 12 15 16 17 19 20 25 26 27 29 30 42 Constituent of cellular water and organic cell materials Constituent of organic cell materials Constituent of proteins, nucleic acids and coenzymes Constituent of cellular water and organic materials, as 0, electron acceptor in respiration of aerobes Principal extracellular cation Important divalent cellular cation, inorganic cofactor for many enzymatic reactions, incl. those involving ATP; hctions in binding enzymes to substrates and present in chlorophylls Constituent of phospholipids, coenzymes and nucleic acids Constituent of cysteine, cystine, methionine and proteins as well as some coenzymes as CoA and cocarboxylase Principal intracellular and extracellular anion Principal intracellular cation, cofactor for some enzymes Important cellular cation, cofactor for enzymes as proteinases Inorganic cofactor cation, cofactor for enzymes as proteinases Constituent of cytochromes and other heme or non-heme proteins, cofactor for a number of enzymes Constituent of vitamin B,, and its coenzyme derivatives Inorganic constituents of special enzymes