BIOINORGANIC CHEMISTRY A Short Course Second Edition

190 GROUP I AND II METALS IN BIOLOGICAL SYSTEMS

TABLE 5.1 Characteristics of Group I and II Ions in Biological Species Ion

Radius (

Å )/

Coordination

No.

Concentration (mM)

Carriers, Facilitators, Enzymes,

Cofactors Function/Toxicity

Extracellular

(BloodPlasma)

Intracellular (Red Blood

Cells)

H

+^

Maintain pH

Li

+^

0.60

Medicinal usage against hyperactivity

Na

+^

0.95/6(+)

160

11

Sodium channels, ionophores,

Na

+ /K

+ ATPase, sodium pump

Electroneutrality, nerve action activation,

osmotic pressure control, maintain ionic strength outside cell (as NaCl), maintain cell potential

K

+^

1.33/8( ± )

10

92

Potassium channels, ionophores,

Na

+ /K

+ ATPase, sodium pump

(K

+ site), pyruvate kinase,

dioldehydratase

Electroneutrality, nerve action activation,

osmotic pressure control, maintain ionic strength inside cell (as KCl), maintain cell potential

Rb

+^

1.48

Toxicity — may compete with K

+ in

potassium channels

Cs

+^

1.67

Cytotoxic, chromosomal aberrations

in mice

3

Be

2+

0.31

Pulmonary tumors,

4 may impair some

vascular endothelial functions and alter the interaction between platelet and endothelial mediators

5