Loss of Co²⁺ sensitivity of monkey brain cytosolic neutral α-D-mannosidase by cyclic AMP dependent phosphorylation

Abstract

α-D-Mannosidase that exhibits a pH optimum close to neutrality (neutral mannosidase) purified from monkey brain cytosol is known to be stimulated by Co²⁺ and this stimulation is suggested to be mediated through a Co²⁺ activated aminopeptidase that is inseparable from the neutral mannosidase and that cleaves amino acids from the neutral mannosidase. In the present studies, the phosphorylation on serine residues of the neutral mannosidase by cyclic AMP dependent protein kinase is demonstrated. After phosphorylation the mannosidase activity remained unchanged, but it was not stimulated by Co²⁺. The aminopeptidase activity, although it retained its response to stimulation by Co2+, showed a drastic reduction in its activity after phosphorylation. It is suggested that the loss of Co²⁺ sensitivity of the neutral mannosidase after phosphorylation is mediated through the aminopeptidase.