cytochorme b 6 /f complex, ferredoxin, and cytochrome c). In addition, the abundant soluble manganese in the early ocean was utilized in the wateroxidizing centers of photosystem II. The combined
action of these iron- and manganese-containing
biological redox catalysts provided for efficient fixation of N 2 and CO 2 needed for production of proteins and other biological compounds. The
concomitant release of O 2 from photosynthesis and
sequestration of organic carbon in marine sediments
and sedimentary rocks, slowly (over 1–2 billion
years) oxidized ferrous iron to ferric oxides and
sulfide species to soluble sulfate, ultimately resulting
in the buildup of free O 2 first in the surface ocean
and atmosphere, and gradually in the ocean as a
whole. The precipitation of ferric oxides from the sea
has resulted in the chronic Fe limitation of carbon
fixation and N 2 fixation that we currently observe in
the ocean. However, this negative effect is more than
balanced by the usefulness of molecular oxygen in
highly efficient oxygen-dependent respiration utilized
by all present-day aerobic microbes, plants, and
animals. Furthermore, the release of zinc, copper,
molybdenum, and cadmium from insoluble sulfides
allowed for the subsequent evolution of numerous
new enzymes utilizing these metals, which appear to
have evolved following the appearance of free O 2 .
Thus, evolution has involved a continuous feedback
between biological systems and the surrounding
chemical environment, with biological trace metal
catalysts playing a central mediating role in this
process.
Glossary
ATP Adenosine triphosphate; a high-energy
compound produced in photosynthesis and
respiration which is used as the main energy
currency of cells.
Chemical speciation The different chemical forms
of trace elements.
Chelate A strong complex between an organic
ligand and a metal.
Chelation The reaction of a metal with an organic
ligand to form a chelate.
Chelator An organic ligand that forms stable
complexes with metal ions.
Cytochrome b 6 /f complex An iron-rich protein
complex involved proton pumping and ATP
synthesis in photosynthesis.
Fe(II), Fe(III) Iron with oxidation states of þ 2 and
þ 3, respectively, also referred to as ferrous and
ferric iron.
Ferredoxin A soluble iron–sulfur protein involved
in photosynthetic electron transport.
Ferric hydrolysis species Inorganic complexes of
iron(III) with one to four hydroxide ions: FeOH
2 þ ,
FeðOHÞ
þ
2 , Fe(OH) 3 , and FeðOHÞ
À
4 .
Metalloenzyme An enzyme containing a metal as
an essential functional component.
Mn(II), Mn(III), Mn(IV) Manganese with oxidation
states of þ 2, þ 3, and þ 4, respectively.
NADPH The reduced form of nicotinamide
adenine dinucleotide phosphate, which is
produced in photosynthesis and serves as the
primary reductant molecule in plant cells.
Nitrogenase An iron-containing enzyme complex
responsible for nitrogen fixation.
Photosystem I and photosystem II The two
photochemical reaction centers in photosynthesis.
Redox Chemical reduction and oxidation.
Siderophore A
high-affinity
organic
ligand
produced by bacteria to complex iron and
facilitate its intracellular uptake.
Superoxide radical A free radical of chemical
structure (dO
À
2 ) formed from the single electron
reduction of molecular oxygen.
See also
Carbon Cycle. Iron Fertilization. Nitrogen Cycle.
Transition Metals and Heavy Metal Speciation.
Further Reading
Anbar AD and Knoll AH (2002) Proterozoic ocean
chemistry and evolution: A bioinorganic bridge? Science
297: 1137--1142.
Barbeau K, Rue EL, Trick CG, Bruland KW, and Butler A
(2003) Photochemical reactivity of siderophores
produced by marine heterotrophic bacteria and
cyanobacteria based on characteristic Fe(III) binding
groups. Limnology and Oceanography 48: 1069--1078.
Boyle E, Edmond JM, and Sholkovitz ER (1977) The
mechanism of iron removal in estuaries. Geochimica
Cosmochimica Acta 41: 1313--1324.
Brand LE, Sunda WG, and Guillard RRL (1983)
Limitation of marine phytoplankton reproductive rates
by zinc, manganese and iron. Limnology and
Oceanography 28: 1182--1198.
Bruland KW (1989) Complexation of zinc by natural
organic ligands in the central North Pacific. Limnology
and Oceanography 34: 269--285.
Bruland KW (1992) Complexation of cadmium by natural
organic ligands in the central North Pacific. Limnology
and Oceanography 37: 1008--1017.
Bruland KW and Franks RP (1983) Mn, Ni, Cu, Zn and Cd
in the western North Atlantic. In: Wong CS, Boyle E,
Bruland KW, Burton JD, and Goldberg ED (eds.)
TRACE ELEMENT NUTRIENTS 27
action of these iron- and manganese-containing
biological redox catalysts provided for efficient fixation of N 2 and CO 2 needed for production of proteins and other biological compounds. The
concomitant release of O 2 from photosynthesis and
sequestration of organic carbon in marine sediments
and sedimentary rocks, slowly (over 1–2 billion
years) oxidized ferrous iron to ferric oxides and
sulfide species to soluble sulfate, ultimately resulting
in the buildup of free O 2 first in the surface ocean
and atmosphere, and gradually in the ocean as a
whole. The precipitation of ferric oxides from the sea
has resulted in the chronic Fe limitation of carbon
fixation and N 2 fixation that we currently observe in
the ocean. However, this negative effect is more than
balanced by the usefulness of molecular oxygen in
highly efficient oxygen-dependent respiration utilized
by all present-day aerobic microbes, plants, and
animals. Furthermore, the release of zinc, copper,
molybdenum, and cadmium from insoluble sulfides
allowed for the subsequent evolution of numerous
new enzymes utilizing these metals, which appear to
have evolved following the appearance of free O 2 .
Thus, evolution has involved a continuous feedback
between biological systems and the surrounding
chemical environment, with biological trace metal
catalysts playing a central mediating role in this
process.
Glossary
ATP Adenosine triphosphate; a high-energy
compound produced in photosynthesis and
respiration which is used as the main energy
currency of cells.
Chemical speciation The different chemical forms
of trace elements.
Chelate A strong complex between an organic
ligand and a metal.
Chelation The reaction of a metal with an organic
ligand to form a chelate.
Chelator An organic ligand that forms stable
complexes with metal ions.
Cytochrome b 6 /f complex An iron-rich protein
complex involved proton pumping and ATP
synthesis in photosynthesis.
Fe(II), Fe(III) Iron with oxidation states of þ 2 and
þ 3, respectively, also referred to as ferrous and
ferric iron.
Ferredoxin A soluble iron–sulfur protein involved
in photosynthetic electron transport.
Ferric hydrolysis species Inorganic complexes of
iron(III) with one to four hydroxide ions: FeOH
2 þ ,
FeðOHÞ
þ
2 , Fe(OH) 3 , and FeðOHÞ
À
4 .
Metalloenzyme An enzyme containing a metal as
an essential functional component.
Mn(II), Mn(III), Mn(IV) Manganese with oxidation
states of þ 2, þ 3, and þ 4, respectively.
NADPH The reduced form of nicotinamide
adenine dinucleotide phosphate, which is
produced in photosynthesis and serves as the
primary reductant molecule in plant cells.
Nitrogenase An iron-containing enzyme complex
responsible for nitrogen fixation.
Photosystem I and photosystem II The two
photochemical reaction centers in photosynthesis.
Redox Chemical reduction and oxidation.
Siderophore A
high-affinity
organic
ligand
produced by bacteria to complex iron and
facilitate its intracellular uptake.
Superoxide radical A free radical of chemical
structure (dO
À
2 ) formed from the single electron
reduction of molecular oxygen.
See also
Carbon Cycle. Iron Fertilization. Nitrogen Cycle.
Transition Metals and Heavy Metal Speciation.
Further Reading
Anbar AD and Knoll AH (2002) Proterozoic ocean
chemistry and evolution: A bioinorganic bridge? Science
297: 1137--1142.
Barbeau K, Rue EL, Trick CG, Bruland KW, and Butler A
(2003) Photochemical reactivity of siderophores
produced by marine heterotrophic bacteria and
cyanobacteria based on characteristic Fe(III) binding
groups. Limnology and Oceanography 48: 1069--1078.
Boyle E, Edmond JM, and Sholkovitz ER (1977) The
mechanism of iron removal in estuaries. Geochimica
Cosmochimica Acta 41: 1313--1324.
Brand LE, Sunda WG, and Guillard RRL (1983)
Limitation of marine phytoplankton reproductive rates
by zinc, manganese and iron. Limnology and
Oceanography 28: 1182--1198.
Bruland KW (1989) Complexation of zinc by natural
organic ligands in the central North Pacific. Limnology
and Oceanography 34: 269--285.
Bruland KW (1992) Complexation of cadmium by natural
organic ligands in the central North Pacific. Limnology
and Oceanography 37: 1008--1017.
Bruland KW and Franks RP (1983) Mn, Ni, Cu, Zn and Cd
in the western North Atlantic. In: Wong CS, Boyle E,
Bruland KW, Burton JD, and Goldberg ED (eds.)
TRACE ELEMENT NUTRIENTS 27