Fig. 9. Effects of N-acetylneuraminic acid (NANA) on cAMP-dependent protein kinase (PKA) activity in whole-tentacle homogenate. Tentacles were harvested, pooled and gently homogenized on ice in extraction buffer, pH6.8, with 10 strokes of a Dounce all-glass homogenizer. Homogenates including 0.1mmoll^-1 GTP and 0.1mmoll^-1 ATP were stored on ice for 15min in the presence (filled columns) and absence (open columns) of 1.8x10^-5moll^-1 NANA, after which 40µl samples were taken for PKA assay at 30°C for 10min. The addition of 20nmoll^-1 PKA inhibitor (PKI) completely blocked the PKA activity both in the presence and in the absence of NANA. The protein concentration of the homogenate was 528µgml^-1. Data are expressed as pmoles of phosphate transferred per minute. Each data point represents the mean ± S.E.M. (n=4 samples).