Effects of Sugars on Glycosidase Secretion in Dictyostelium discoideum

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Abstract
When exponentially growing D. discoideum amebae were harvested from growth medium and suspended in a nutrient-free phosphate buffer, the cells released 20-30% of their total .beta.-N-acetylglucosaminidase and .alpha.-mannosidase activities. This release was inhibited by sodium azide but stimulated (to a level of 90% release) by various saccharides when added to the phosphate buffer at millimolar concentrations. Various salts, amino acids and nucleotides were unable to stimulate the release process. Non-metabolizable sugars were more stimulatory than metabolizable sugars, but no clear distinction related to structure, ability to be transported or ability to be metabolized accounted directly for the varying effects of the sugars on glycosidase release. The rate and amount of glycosidase release was dependent on the sugar concentration but not on the cell density. Sugars probably stimulate a specific release of a variety of lysosomal enzymes and the relationship of this release to D. discoideum morphogenesis is discussed.