Figure 1. A factor in sperm extracts is able to compete for [³²P]NAADP binding.

A, inhibition of [³²P]NAADP binding to egg homogenates by the three different sperm homogenate preparations and authentic NAADP. B, representative concentration-response curves obtained from competition binding experiments with sperm extract (Aug 00, ▪-▪) and NAADP (○--○). Units for sperm homogenate are expressed as % volume/200 μl binding reaction. Data are presented as means ±s.e.m.; n = 3-9.