Cytosolic AMP deaminase (AMPD) catalyzes the hydrolysis of AMP to yield IMP and ammonia. Three isoforms of AMPD, E, L, and M, have been identified that differ in their expression patterns in the body. All occur as tetramers and all have qualitatively the same catalytic activity, however (Bausch-Jurken et al. 1992; Mahnke-Zizelman et al. 1998).