Stimulation by ATP-Mg²⁺ and inactivation by cyclic-AMP-dependent phosphorylation of a cytosolic monkey brain aminopeptidase

Abstract

The activity of a purified cytosolic aminopeptidase (Mr 79,000) from monkey brain was stimulated about 4-fold by ATP-Mg²⁺. The stimulation was seen with either synthetic aminopeptidase substrates or natural peptides such as enkephalins. Both ATP and Mg²⁺ were required for stimulation, and ADP did not inhibit the stimulation. Non-hydrolysable analogues of ATP, deoxy-ATP and other nucleoside triphosphates stimulated to a lesser extent compared with ATP, whereas nucleoside mono- or di-phosphates were ineffective. The enzyme did not exhibit any ATPase activity. An ATPase inhibitor, orthovanadate, had no inhibitory effect on the ATP-Mg²⁺ stimulation. The aminopeptidase was not autophosphorylated by [gamma-32P]ATP and Mg2+, but in the presence of cyclic AMP-dependent protein kinase underwent phosphorylation on serine residue(s). Phosphorylation resulted in inactivation of the aminopeptidase activity, and also resulted in a decreased stimulation of the enzyme by ATP-Mg²⁺.