FIGURE 3.
ApbC proteins activate Leu-1 at variable rates. A, time course of ApbC- (•) or ApbCK121A (○)-dependent Leu-1 activation. Leu-1 activity was monitored at fixed time points by the formation of isopropylmaleate, which was monitored at A235. Assays contained 4 μm reconstituted ApbC and 3.5 μm apo-Leu-1. The reaction was started by adding ApbC to the reaction vessel. B, plot of 1/[holo-ApbC protein] versus time post ApbC protein addition. The second-order rate constant of cluster transfer was determined by fitting the data using linear regression. The concentration of holo-ApbC protein at a given time point was estimated using Equation 1.