Deaminase

Deaminase is a class of enzymes that catalyze deamination—the removal of an amino group from a molecule, typically converting an amine into a carbonyl group with the release of ammonia. In biology, deaminases participate in metabolism of nucleotides and amino acids, and in the editing of genetic information by altering nucleic acids.

Nucleic acid deaminases include cytidine deaminases, which convert cytidine to uridine, and adenosine deaminases, which convert adenosine to inosine in RNA. Prominent families include AID and APOBEC (AID/APOBEC) enzymes that deaminate cytidine and are involved in antibody gene diversification and innate antiviral defense, and ADARs which edit adenosine to inosine in double-stranded RNA.

Most cytidine deaminases are zinc-dependent enzymes and use a catalytic zinc ion coordinated by conserved residues. The deamination reaction alters the nucleobase, changing base pairing and potentially producing mutations in DNA or RNA depending on substrate and context. In some enzymes, the activity is restricted to RNA or DNA substrates, influencing the form and consequences of editing.

Biological roles are diverse. Adenosine deaminase (ADA) participates in purine metabolism; AID- and APOBEC-family deaminases drive somatic hypermutation and class switch recombination in B cells, and APOBEC3 enzymes provide intrinsic antiviral activity. ADAR-mediated RNA editing can affect transcript processing, stability, and protein function.

Clinical and research relevance includes immunodeficiency when deaminase activity is disrupted (for example, ADA deficiency), and mutagenesis linked to cancer from off-target deaminase activity. Deaminases are also explored for biotechnological genome and transcript editing, highlighting both therapeutic potential and the need to control off-target effects.