Figure 7.

Steady-state kinetics for the asccφ28 encapsidation protein. (a) The gp11 ATPase produces ADP from ATP. Two subsequent enzymatic steps result in the conversion of NADP to NAD+, which is measured with a spectrophotometer. ATP hydrolysis by gp11 is the limiting reaction step, with all other reactants in large excess, so the ATP hydrolysis rate can be correlated with the measured reduction in NADP. (b) The upper blue plot represents the ATP substrate, and the lower magenta plot represents GTP. The 10-fold lower K_m for ATP indicates that gp11 is primarily an ATPase.