Résumé
Ammodytoxin is a presynaptically neurotoxic (β-neurotoxic) snake venom secretory phospholipase A2 (sPLA2). We detected a 25 kDa protein which binds the toxin with very high affinity (R25) in porcine cerebral cortex [Vučemilo et al., Biochem. Biophys. Res. Commun. 251 (1998) 209–212]. Here we show that R25 is an integral membrane protein with intracellular localisation. It is the first sPLA2 receptor known to date that localises to intracellular membranes. Centrifugation on sucrose gradients was used to fractionate porcine cerebral cortex. The subcellular composition of the fractions was determined by following the distribution of organelle-specific markers. The distribution of R25 in the fractions matched the distribution of the mitochondrial marker succinate dehydrogenase, but not the markers for plasma membrane, lysosomes, endoplasmic reticulum, synaptic and secretory vesicles. R25 most likely resides in mitochondria, which are known to be targets for sPLA2 neurotoxins in the nerve ending and are potentially implicated in the process of β-neurotoxicity.