Manganese is an essential trace element in all domains of life, and manganese-dependent enzymes catalyze a wide range of reactions including hydrolysis, phosphorylation, water oxidation, nucleotide reduction, and protection against oxidative stress. Dinuclear manganese-containing cofactors are both homonuclear and heteronuclear centers. Due to its rich redox chemistry, manganese is found in a number of redox-active enzymes, where the oxidation state of the metal ion ranges from Mn^II to Mn^IV. Non-redox-active metal sites are found in, for example, sweet potato purple acid phosphatase (Mn^IIFe^III), concanavalin A (Mn^IICa^II), arginase (Mn^II₂), and prolidase (Mn^II₂). Proteins with redox-active Mn-containing dinuclear centers generally belong to the ferritin-like superfamily. Whereas most members of the superfamily have an Fe₂ center, Mn-containing metal sites are found in Mn catalase (Mn₂), some RNR β subunits (subclasses Ib and Id have Mn₂, and subclass Ic has MnFe), and R2lox (MnFe). In addition, a member of DNA-binding protein from starved cells (Dps) can form an MnFe center. No manganese chaperones are known and Mn-dependent enzymes plausibly acquire their metals directly from the intracellular pool of Mn²⁺, which is balanced via different import and efflux transporter systems:

• Mn catalase catalyzes the disproportionation of the reactive species hydrogen peroxide by alternating between Mn^III₂ and Mn^II₂ in two consecutive reactions, detoxifying two hydrogen peroxide molecules to oxygen and water.
• RNR subclass Ib β subunit has an oxidized metal center and a tyrosyl radical. It initially binds Mn²⁺ and forms a complex with a specific flavodoxin-like protein that oxidizes the metal center to a transient Mn^IV/III species, which converts to the active Mn^III₂-Tyr^• cofactor.
• RNR subclass Ic β subunit has an Mn^IVFe^III cofactor. It is formed by O₂ oxidation of a Mn^IIFe^II center, and the initial transient Mn^IVFe^IV center is reduced to the active cofactor via an external electron transfer pathway.
• RNR subclass Id β subunit is suggested to contain an oxidized Mn₂ center formed in the absence of a flavodoxin-like maturase and lacks the tyrosyl radical.
• R2-like ligand-binding oxidase (R2lox) has an Mn^IIIFe^III cofactor that is generated from Mn^IIFe^II by O₂ oxidation. It is assumed that an Mn^IVFe^IV intermediate generates a valine–tyrosine cross-link adjacent to the metal site.

Despite the apparent simplicity of manganese cofactor assembly, nature has developed a number of different methods to control the metalation of manganese proteins and activate the relatively redox-inert Mn^II ion.