Biochemistry, Vol. 37, No. 3. (20 January 1998), pp. 792-799. The processivity of the microtubule-kinesin ATPase has been investigated using stopped-flow kinetic methods to measure the binding of each motor domain of the dimeric kinesin (K401) to the microtubule and the release of the fluorescent ADP analog, 2'(3')-O-(N-methylanthraniloyl)adenosine 5'-diphosphate (mantADP) from the active site of the motor domain. The results show that the release of two molecules of ADP from dimeric kinesin (K401) after the binding of kinesin ADP to the microtubule is a sequential process leading to biphasic kinetics. The maximum rate of release of mantADP from the first motor domain of K401 or monomeric K341 is fast (300 s-1) and independent of added nucleotide. The rate of mantADP release from the second motor domain of K401 is slow in the absence of added nucleotide (0.4 s-1) and reaches a maximum rate of 300 s-1 at saturating concentrations of ATP. High concentrations of ADP stimulate mantADP... - Steve Koch

This is a wonderful paper by Gilbert, Moyer, and Johnson. In contrast to the companion paper in the same issue ('link':http://www.citeulike.org/user... ), this is a more limited set of stopped flow experiments and is much easier to read. They show convincingly that ATP binding to the microtubule-bound head greatly enhances MT-stimulated ADP release by the tethered head. In the absence of ATP, there does seem to still be some MT-stimulated ADP release, which is important for models. This means that it's possible, but much less likely for the kinesin to enter a both heads bound / empty state (it's not clear whether this would be a forward or backward step). The maximal rate of ADP release is either 300/s or 600/s I'm not exactly clear on that. I'm also unsure why it appears their kinesin (drosophila, truncated) is much slower than I expect (maximal rate of 40 / steps per second for the dimer). They show a kinetic scheme in this paper, which is presumably a simplified version of the same scheme from the companion paper ('link':http://www.citeulike.org/user... ). - Steve Koch