ADP release upon MT collision for KIF3AB, KIF3AA, KIF3BB, and KIF3AA + KIF3BB. KIF3AB, KIF3AA, KIF3BB, or mixtures of KIF3AA plus KIF3BB at total 5 μm site concentration were rapidly mixed in the stopped-flow instrument with 40 μm MTs plus 50 μm mantATP (syringe concentrations). The mixtures contain either 25% KIF3AA + 75% KIF3BB (1.25 μm KIF3AA and 3.75 μm KIF3BB), 50% KIF3AA + 50% KIF3BB (2.5 μm KIF3AA and 2.5 μm KIF3BB), or 75% KIF3AA + 25% KIF3BB (3.75 μm KIF3AA and 1.25 μm KIF3BB). Final concentrations were 2.5 μm KIF3 site concentration, 20 μm MTs, and 25 μm mantATP. A, individual transients show a biphasic increase in mantATP fluorescence as a function of time. B, the experimental transients for the mixtures of KIF3AA + KIF3BB in comparison with the transients of KIF3AB, KIF3AA (AA), and KIF3BB (BB). C, table of the observed rates of ADP release.