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hν
Hg - Hg HgMe 2
2+
reductase
MeI, hν
Hg(SMe) 2 MeHgI Me -
MeS - Cl -
Me -
HgSMe + MeHgCl HgCl 2
H + lyase H S
Me + 2
MeHgSMe MeHgSH biogenic
oxidation

HgMe + HgS
2
acetate, HgMe +
Speciation of mercury hν

223

11. The role of the alkaline metals and alkaline earth metals

+
+
Physiologically relevant are the alkaline metal ions Na und K , and the alkaline earth
2+
2+
+
metal ions Mg und Ca . Li is of therapeutic interest (treatment of mood disorders such as
2+
maniac depression; treatment of hypertension). The transition metal ion Mn exhibits some
2+
2+
similarities with Ca und Mg .

Amounts present in man (in g per 70 kg body weight)): Na 105, K 140, Mg 35, Ca 1050 g
Daily demand: Na 1.1-3.3, K 2.0-5.0, Mg 0.3.0.4, Ca 0.8-1.2 g.

2+
With the exception of Mg , there are striking differences in the intra- and extra-cellular
concentrations of these cations. The following Table summarises the intra- and extracellular
concentrations of the more important cations and anions. The Table also contains
concentrations of these ions in sea-water, often considered “the cradle of life“. To maintain the
“correct” concentration gradients between the cytosol and the extracellular space is of prime
importance to ascertain the specific functions of these ions, such as controlling the osmotic
pressure and cell membrane potentials, triggering signal transduction, and activating enzymes.

Table: Concentrations of selected ions (mM) in the intracellular and extracellular space (mean
values for all human cell types, and data for erythrocytes and blood plasma are listed). For
comparison, ion concentrations in sea water are also provided.

2-
K + Na + Ca 2+ Mg 2+ Cl - HCO 3 - HPO 4 2- SO 4
Intracellular 92 11 0.1 2.5 - 155 190
in erythrocytes
Blood plasma 5 152 2.5 1.5 130 195 30
Sea water 10 500 10 50 500 variabel 0.002 29
Intracellular 155 10 0.001 15 8 10 65 0.5
mean value
Extracellular 4 142 2.5 0.9 120 27 1 10
mean value