Figure 3

Determination of specific activity, Km Kemptide and ATP for human Cα2. Panel A: Specific activity of expressed Cα2 and Cα1 was determined to 18 ± 3 and 28 ± 4 units/mg, respectively. Note the lower activity of expressed Cα2 compared to Cα1. Km values for the PKA specific substrate Kemptide and ATP were determined by incubating recombinant Cα2 in the presence of increasing concentrations (1 to 500 μM) of the heptapeptide Kemptide (panel B) and ATP (panel C). Indirect spectrophotometric analyses of ATP consumption as measurement for Cα2 activity (see Methods) indicate a Km for Kemptide of 27.8 ± 2.3 μM (n = 2) and Km ATP of 11.5 ± 0.5 μM (n = 2), see insets panel B and C.