ABSTRACT
Development of the cellular slime mould Dictyostelium discoideum strain NC4, in the presence of α-chymotrypsin (3 mg/ml) is reversibly arrested at the tight aggregate stage (10/12 h). Pronase has a similar effect, but trypsin only retards normal development by about five hours. Normally developing cells are susceptible to α-chymotrypsin if they are transferred into its presence at any time up to the tight aggregate stage (10-12 h). Transfer after this stage does not affect the appearance of fruiting body structures in the normal time (24 h).
Electron microscopy showed the ultrastructure of α-chymotrypsin-blocked aggregates after starvation for 24 h to be consistent with a block at 10 –12 h of normal development. Poorly developed prespore vacuoles, having thin incomplete walls and a paucity of electrondense material, are present in some cells. No angular vacuolated cells characteristic of stalk cells are visible. Fruiting bodies formed in the presence of a α-chymotrypsin, either as minority structures when the enzyme is added before 10 –12 h of normal development, or as the majority structures on later enzyme addition, were found to be abnormal. Normal stalks were formed but the spores were immature. Prespore vacuoles were present, though disrupted, and the cells were not encapsulated by spore walls.
The electronegativity of intact slime mould amoebae was significantly reduced, and material containing L-[6-3H]-fucose and [l-14C]leucine was removed from the cell surface on α-chymotrypsin treatment. Few plasma membrane proteins were affected, however, and staining of polyacrylamide gels for glycopeptides using Con A-peroxide binding also showed little change.