AMP-deaminase (AMPD, EC 3.5.4.6), which catalyzes the irreversible hydrolytic deamination of AMP to IMP and ammonia, is an important energy-related enzyme. The partial genomic sequence of the gene encoding myoadenylate deaminase (AMPD1) from the teleost fish Platichthys flesus was determined. The amino acid sequence of P. flesus AMPD1 shows 82% homology with that of the teleost fish Danio rerio. Comparison of genomic sequences of P. flesus and Rattus norvegicus reveals a high degree of conservation of both sequence and structural organization. A phylogenetic analysis of AMPD sequences shows that bony fish and mammalian AMPD1s arise by duplication of a common primordial gene.