Dictyostelium discoideum spore germination: increases in proteinase activity are not directly coupled to the emergence of myxamoebae

SUMMARY: The accumulation of proteinase activity during the germination of Dictyostelium discoideum spores was examined under conditions in which the timing of germination events was varied. Spores had a single major proteinase, the aspartic proteinase ddAP58 (proteinase E), while the extracellular matrix which surrounds the spores in the fruiting body contained a number of lower-Mr cysteine proteinases, the most active being ddCP18. Very little peptide-nitroanilide-hydrolysing activity was detectable in spores, although some was associated with the matrix. During spore germination there were large increases in activity towards N-carbobenzoxy-L-tyrosyl-L-lysyl-L-arginine 4-nitroanilide and N-benzoyl-L-prolyl-L-phenylalanyl-L-arginine 4-nitroanilide. The enzymes responsible for these activities (referred to as ZYKRase and BzPFRase respectively) were not identical as BzPFRase was much more sensitive to the cysteine proteinase inhibitor E-64 than was ZYKRase. When spores were heatactivated, the increases in activity coincided with the emergence of myxamoebae and the appearance of cysteine proteinases detected using electrophoresis in gelatin gels. For autoactivated spores, emergence was delayed by 0·5 to 1 h and proteinase accumulation lagged slightly behind emergence. If the spores were activated with DMSO, or if heat-activated spores were treated with sucrose after swelling, proteinase accumulation proceeded more rapidly than emergence. Thus temporal control of the accumulation of proteinases during germination varies according to the conditions used. In heat-activated spores, the timing of the increase was similar to that observed previously for β-glucosidase and trehalase, but the temporal controls were not the same as those for the latter enzymes when the other activation conditions were used. The results show that proteinase accumulation is not directly coupled to emergence but could be more closely linked to the late swelling stage which precedes emergence.