CAPS2 and the related protein CAPS1 encode novel neural/endocrine-specific cytosolic and peripheral membrane proteins. Both are essential components of the synaptic vesicle priming machinery and are required for the Ca2+-regulated exocytosis of secretory vesicles; CAPS-deficient neurons contain no or very few fusion competent synaptic vesicles, causing a selective impairment of fast phasic transmitter release. Like CAPS1, numerous isoforms of CAPS2 are known to exist. These isoforms show distinct expression patterns in the brain. For example, CAPS2b showed high expression in the developing cerebellum. Furthermore, one version of CAPS2 mRNA that lacks exon 3 is detected in some autistic patients, suggesting that the differential expression pattern of CAPS2 is involved in neuronal development. This CAPS2 antibody is predicted to be specific to CAPS2 and not recognize CAPS1.