Metal-binding cofactors

Molybdopterin is the metal-binding cofactor in the molybdenum- and tungsten dependent oxidoreductases [78,79]. 

Cofactors serve functions similar to those of prosthetic groups but bind in a transient, dissociable manner either to the enzyme or to a substrate such as ATP. Unlike the stably associated prosthetic groups, cofactors therefore must be present in the medium surrounding the enzyme for catalysis to occur. The most common cofactors also are metal ions. Enzymes that require a metal ion cofactor are termed metal-activated enzymes to distinguish them from the metalloenzymes for which metal ions serve as prosthetic groups. 

For all these reasons, some chemical or genetical modifications have been applied into the binding sites of antibodies in order to improve their reactivity [22]. Antibodies can be modified by the incorporation of natural or synthetic catalysts into the antibody recognition site, as for instance transition metal complexes, cofactors, and bases or nucleophiles, to carry other catalytic functions, which open the way to... 

The antitumor antibiotic bleomycin (BLM) is believed to cause cytotoxicity through its ability, in the combined presence of dioxygen and a metal ion cofactor (204), to bind to and degrade DNA (205). Iron complexes of BLM have aroused special attention, as such complexes are the first (vide supra concerning the discussion of hemerythrin and hemocyanin) non-heme-iron complexes with a significant capacity for dioxygen activation (206). 

As a rule /3-lactamase activity does not depend on specific activators or cofactors. The only exception so far is j3-lactamase II which requires Zn2+ for stability and activity 87). The metal binding characteristics of this enzyme have been described in a recent study 66). In other cases where the ion content of the assay medium may affect the activity 43,44), no absolute requirements were demonstrated. 

Metallochaperones see Metallochaperones Metal Ion Homeostasis) are metal-binding proteins (Li) designed to deliver the appropriate metal ion or metal cofactor to a target ligand (L2), as illustrated in equation (2). 

Although the different sequences and folds of proteins provide the most disparate metal binding sites (some examples of which are provided in Fig. 3), Nature has evolved to select other organic or inorganic ligands for metal ions in proteins, which we call special metal cofactors. These cofactors can be grouped into two broad classes tetrapyrroles and metaUoclusters. 

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