Interaction of Dictyostelium discoideum alpha-mannosidase with beef liver phosphomannosyl receptor. Effect of alkaline phosphatase treatment.

Both intracellular and secreted alpha-mannosidase from D. discoideum bind quantitatively and specifically to immobilized phosphomannosyl receptor from beef liver. Almost all the intracellular enzyme molecules retain tight binding capacity subsequent to exhaustive alkaline phosphatase treatment. This supports the idea that uncovered phosphates are not essential for optimal recognition by the phosphomannosyl receptor. However, approximately 50% of the extracellular enzyme was converted to a weak binding form by the same treatment.