Table 1.

Some metalloproteins and their functions in microalgae and cyanobacteria.

Metal	Enzyme(s)	Function(s) in a Cell
Fe	Cytochromes	Electron transport during photosynthesis and respiration
	Other Fe-S proteins
	Ferredoxin	Electron transport during photosynthesis and nitrogen fixation
	NAD(P)H/PQ-oxidoreductase	Electron transport during photosynthesis
	Nitrate and nitrite reductase	Converting nitrates to ammonia
	Chelatase	Synthesis of porphyrin and phycobiliprotein
	Nitrogenase *	Nitrogen fixation
	Catalase	Protection of the cell from reactive oxygen species
	Peroxidase
	Superoxide dismutase
Zn	Carbonic anhydrase	Hydration and dehydration of CO2
	Alkaline phosphatase	Hydrolysis of Phosphoric Acid Esters
	RNA polymerase	Replication and transcription of nucleic acids
	tRNA synthetase	tRNA synthesis
	Reverse transcriptase	Synthesis of single-stranded DNA from RNA
	Carboxypeptidase	Hydrolysis of peptide bonds
	Superoxide dismutase	Protection of the cell from reactive oxygen species
Cu	Multicopper ferroxidase	High-affinity transmembrane Fe transport
	Superoxide dismutase	Protection of the cell from reactive oxygen species
	Ascorbate oxidase	Oxidation and reduction of ascorbic acid
	Cytochrome oxidase	Mitochondrial electron transport
	Plastocyanin	Electron transport during photosynthesis
Mn	Phosphotransferases	Phosphorylation reactions
	Arginase	Hydrolysis of arginine to ornithine and urea
	Superoxide dismutase	Protection of the cell from reactive oxygen species
	O2-releasing enzymes	Water oxidation during photosynthesis
Mo	Nitrate reductase	Converting nitrates to ammonia
	Nitrogenase *	Nitrogen fixation
Ni	Superoxide dismutase	Protection of the cell from reactive oxygen species
	Urease	Hydrolysis of urea
Co	Vitamin B12	Carbon and hydrogen transfer reactions

* In free-living and symbiotic diazotrophs.