Screening of enzymatic mechanisms possible involved in membrane fusion during exocytosis in Paramecium cells.

Microinjected alkaline phosphatase triggered exocytosis of trichocysts. Among a variety of inhibitors and stimulators interfering with fusogenic mechanism discussed in the literature, only phosphatase inhibitors inhibited exocytosis. Various other enzymes were also tested with a new in vitro system (Vilmart-Seuwen et al., 1986), but results were mostly negative. (The possible involvement of proteases remains questionable.) Positive results obtained with micro-injected alkaline phosphatase are in line with our previous results: (a) The occurrence of a cytochemical reaction for phosphatase activity precisely at fusion sites (Plattner et al., 1980); (b) the occurrence of protein dephosphorylation during exocytosis (Gilligan and Satir, 1982; Zieseniss and Plattner, 1985) and (c) the negative modulatory effect of ATP on exocytotic membrane fusion (Vilmart-Seuwen et al., 1986).