Binding of actin to chromaffin granules and mitochondrial fractions of adrenal medulla.

Binding of actin to chromaffin granules was confirmed and shown to be salt dependent and eliminated by prior trypsin treatment of the granules. However, purified granules bind less actin than do crude granules. A mitochondria-enriched fraction was found to bind substantially more actin per mg protein than did the secretory vesicle fraction. Binding of actin by the secretory vesicles therefore is not a good indication that actin plays an active role in exocytosis.