We cloned cDNAs econoding four adenylate kinase (AK) isozymes from mouse kindney cDNA library. The AK1, AK2, AK3, and AK4cDNAs encode the 194-, 232-, 227-, and 223-amino acid protains, respectively. AK4 is a recently isolated gane that is highly homologous to the reported human AK3. Northern blot analysis and reverse transcriptionpolymerase chain reaction analysis revealed that AK1 mDNA was predominantly expressed in skeletal muscle, heart, and testis