Clathrin‐associated proteins were separated from clathrin under various clathrin‐denaturing conditions, i.e. heating, freezing and isoelectric precipitation. The proteins retained biological activity; they were purified further by affinity chromatography on calniodulin‐conjugated CNBr‐Sepharose 4B and used for antibody purification. The affinity‐purified anti‐(clathrin‐associated proteins) antibodies gave a fluorescent dotted pattern in cultured fibroblasts consistent with the known distribution of clathrin. Chemical cross‐linking of pure clathrin‐associated proteins indicated that these polypeptides exist as monomers in solution, each possessing Cazi‐dependent affinity Tor calmodulin to which they bind in a 1: 1 molar ratio. Chymotryptic treatment of coated vesicles selectively cleaved the clathrin‐associated proteins into a 15000–18000‐Mr doublet polypeptide. These subfragments retained their Ca2+‐dependent affinity for calmodulin. Our results support a regulatory role for clathrin‐associated proteins in clathrin assemblies.

Endogenous phospholipase A2 activity of brain synaptic vesicles was Ca2+ -dependent and was increased by prostaglandin F2 alpha, calmodulin, adenosine 3', 5' -monophosphate, and adenosine triphosphate, whereas the activity was inhibited by prostaglandin E2 in the absence or presence of calmodulin. Light-scattering measurements demonstrated that stimulation of the enzyme's activity correlated with the induction of vesicle-vesicle aggregation. The effects of these compounds on endogenous synaptic vesicle phospholipase A2 activity may imply a common end point of their purported neuromodulatory actions, and indicate that synaptic vesicle phospholipase A2 may play a central role in presynaptic neurotransmission.