EVIDENCE OF A SPECIES-DIFFERENTIATED REGULATORY DOMAIN WITHIN THE N-TERMINAL REGION OF SKELETAL-MUSCLE AMP-DEAMINASE

Rabbit skeletal muscle AMP deaminase was submitted to limited proteoly sis by trypsin that converts the native 80 kDa enzyme subunit to a sta ble product of approx. 70 kDa, which, in contrast to the native enzyme , is not sensitive to regulation by ATP at pH 6.5. Tryptic peptide map ping indicates that proteolysis is confined to the N-terminal region o f the molecule, identifying in this region of AMP deaminase a non-cata lytic, 95 residue regulatory domain that stabilises the binding of ATP to a distant site in the molecule. Protein sequence analysis reveals a marked degree of divergence between rat and rabbit skeletal muscle A MP deaminases in the regions containing residues 7-12 and 51-52, givin g molecular basis to the hypothesis of the existence of isoenzymes of AMP deaminase in the mature skeletal muscle of the mammals.