C-terminal mutants of syb-2 cause a slowdown of transmitter release. The C-terminal mutants of syb-2 are shown in Fig. 1. (Ai and Bi) Mean secretion in flash-evoked transmitter release is slowed down. (Aii and Bii) Detailed views of normalized traces in Ai and Bi show that the kinetics of release are slowed down in all cases. (Aiii and Biii) Time constants of the RRP and SRP obtained by fitting of exponentials show slowdown of release in the L84A mutant (Aiii: control, n = 19; and L84A, n = 25) and L84N, L84G, and L84D mutations (Biii: control, n > 15; L84D, n = 9/14; L84G, n = 13/17; and L84N, n = 15/19 for RRP/SRP time constants; and *, P < 0.05; **, P < 0.01; and ***, P < 0.001 in t test). (Ai, Aiii, Bi, and Biii) Mean ± SEM is shown.