Interaction of AMP deaminase with RNA

tRNA, 18 S and 28 S ribosomal RNAs were found to activate muscle AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) but inhibit liver and heart AMP deaminases. The macromolecular structures are essential for modulation of enzyme activity, since the effects of RNA disappeared after RNAase treatment. Sucrose density centrifugation experiments clearly demonstrated the binding of purified muscle AMP deaminase to tRNA, 18 S and 28 S RNAs. The binding is reversible and responsive to alterations of pH and KCl concentration. The binding was stable at pH 5.1–7.0 in 0.1 M KCl, but most of the enzyme dissociated at pH 7.5. KCl below 0.1 M concentration had no effect on dissociation of enzyme-RNA complex, but in 0.15 M KCl the complex was partially dissociated and in 0.2 M KCl most of the enzyme was released. Various nucleotides were also effective in dissociation of the enzyme from complex. The binding is saturable and the maximum number of muscle AMP deaminase molecules bound per mol 28 S RNA was calculated to be approx. 30. Liver and heart AMP deaminases were also found to interact with RNA.