↵F1-a PC12 cell and tissue homogenates (H) were prepared in homogenization buffer (see Materials and Methods) using a Dounce homogenizer; homogenates were centrifuged 10,000 × g(10 min/4°C) to prepare crude particulate (P1) and soluble (S1) fractions. Values (average of duplicates) are from a representative experiment; phosphorylation reactions used 5 μg of extract protein (0.1 μg for CaMKII); CaMKII was purified as described elsewhere (Waxham et al., 1990). A background value for each phosphorylation condition was obtained with reactions to which extract protein was not added (background was subtracted from each experimental value).