Regulation of lysosomal alpha-mannosidase-1 synthesis during development in Dictyostelium discoideum.

The cellular specific activity of lysosomal alpha-mannosidase-1 increases dramatically during development in Dictyostelium discoideum. alpha-Mannosidase-1 is composed of two subunits (Mr = 58,000 and 60,000) which are derived from a common precursor polypeptide (Mr = 140,000). Using enzyme-specific monoclonal antibodies we have determined that throughout development (a) the relative rate of precursor biosynthesis closely parallels the rate of accumulation of cellular enzyme activity and (b) the newly synthesized precursor is efficiently processed to mature enzyme (t1/2 less than 10 min). This indicates that the developmental accumulation of alpha-mannosidase-1 activity is primarily controlled by de novo enzyme synthesis. Furthermore, the change in the relative rate of enzyme precursor synthesis can be accounted for by an increase in the cellular level of functional alpha-mannosidase-1 mRNA during development.