Table 1.

Major features of metalloproteins in organisms [4,15,21,25,26,42,43,44,45].

Metal	Major Catalytic and Structural Roles
Alkali
Na+	Charge carrier; ionic gradient generation
K+	Charge carrier; ionic gradient generation; enzyme activation
Alkaline earth
Mg2+	Phosphoryl transfer; soft-bond hydrolysis; enzyme activation; chlorophyll ‡
Ca2+	Cell signaling and structural trigger; acid-base catalysis; enzyme activation
Transition †
V	N2 activation; e− transfer
Cr	Cell signaling and potential structural trigger
Mo	N2 activation; e− transfer; hydroxylation (H2O)
W	e− transfer; hydroxylation (H2O)
Mn	O2 evolution (H2O); e− transfer; acid-base catalysis; hydrolysis; Mg2+ surrogate
Fe	O2 activation; e− transfer; acid-base catalysis; hydroxylation (O2); H transfer §; heme ‡
Co	Methyl transfer; isomerization catalysis; e− transfer; H transfer §; cobalamin ‡
Ni	H2, CH4 and CO activation; e− transfer; acid-base catalysis; H transfer §; cofactor F430 ‡
Cu	O2 activation; e− transfer; acid-base catalysis; hydroxylation (O2); H transfer §
Group 12
Zn2+	Acid-base catalysis; strong-bond hydrolysis; enzymes in all EC classes; Zn fingers
Cd2+	Acid-base catalysis in carbonic anhydrase in diatoms

^† Charge is not given for transition metals as it varies with the oxidation state during enzymatic catalysis. ^‡ Mg²⁺-, Fe-, Co-, and Ni-containing cyclic tetrapyrroles are indicated in italics. ^§ H transfer stands for hydrogen transfer.