Fig. 3.

Measurement of the specific activity of PMCA in the raft and non- raft fractions. Fractions #2–4, #5–6, and #7–9 were pooled, and 3 μg of protein from each was assayed for PMCA activity across Ca²⁺ concentrations as described under Methods. The activities were determined in the absence of exogenous CaM. Each point is the mean ± SEM of triplicate determinations of the specific activity in nmol P_i/mg protein/min for the raft and non-raft fractions obtained from the SPMs isolated from 5 animals at 6 mos of age. Curves were plotted with least squares fitting of the data to the Michaelis-Menten equation using Sigma Plot 11. The V_max and K_act values determined in the presence and absence of saturating levels of exogenous CaM are listed in Table 2.