PURIFICATION, CHARACTERIZATION AND SECRETION OF THE LYSOSOMAL TREHALASES OF DICTYOSTELIUM DISCOIDEUM.

The enzyme trehalase I of Dictyostelium discoideum is particulate and is secreted prior to cell aggregation or when cells are starved in phosphate buffer under standard secretion conditions. The secreted enzyme possesses properties common to lysosomal enzymes. It is released efficiently and about 62% of the initial cellular enzyme becomes extracellular. The secretion of trehalase is slightly sensitive to cycloheximide and completely blocked by sodium azide. Secretion is enhanced in the presence of disaccharides such as sucrose, lactose and trehalose. Electrophoretograms of intracellular and secreted enzyme reveal no major processing of the enzyme prior to or during secretion. Trehalase I is the form of the enzyme in dormant spores, germinating spores and vegetative cells. Tunicamycin prevents the formation of recoverable trehalase from germinating spores without affecting germination. D. discoideum trehalase cannot be activated under in vitro conditions known to activate other regulatory trehalases and the enzyme exhibits characteristics typical of a non-regulatory trehalase. Trehalase from myxamoebae of strain AX3 and from the spent growth medium of AX3 has been purified to near homogeneity. The enzyme has an estimated ${\rm K}\sb{m}$ of 1.15 mM and a ${\rm V\sb{max}}$ of 4600 nmoles/min/mg. The enzyme does not utilize sucrose, lactose or maltose as substrates. However, it utilizes $\alpha$-D-glucosyl fluoride efficiently. The molecular weight to trehalase falls in the range of 53 kDa to 225 kDa. Trehalase is a very acidic protein with estimated pI\u27s of 4.0 and less than 2.5. Strain M31, bears a mutation mod A, a direct consequence of which is the reduction of negatively charged components on lysosomal enzymes. This is seen in the altered electrophoretic behaviour of strain M31 trehalase. Although charge characteristics of cellular trehalase of strain M31 are different from the extracellular enzyme, the pI\u27s of both trehalases are identical, i.e., 4.0. The present study demonstrates that D. discoideum trehalase is a typical lysosomal enzyme sharing a number of characteristics with other lysosomal enzymes that have been studied earlier. The lysosomal location of trehalase coupled with its non-regulatory nature implicates a compartmentation mechanism in the regulation of trehalose utilization. Source: Dissertation Abstracts International, Volume: 48-07, Section: B, page: 1871. Thesis (Ph.D.)--University of Windsor (Canada), 1987