Dynamins basal (unassembled) GTPase activity.
On several occasions we have measured WT dynamins GTPase activity in the absence of lipid nanotubes (whilst otherwise maintaining our normal assaying conditions). We have found the activity to range between 1/200 and 1/1000 of that observed when lipid nanotubes are included. (This variability is probably in part due to the low signal that we are measuring and consequent high relative background and error values in addition to variations in dynamin preparations and degree of self assembly.) This corresponds to Kcats in the approximate range of 0.002-0.01s-1. This is lower but roughly comparable to the figure of 0.04s-1 quoted by Sever et. al. 1, although their value was determined under lower ionic strength conditions (50mM as compared to 150mM). It is however similar to values reported by Binns et. al. 7 (0.0046 to 0.0061s-1) under high salt assay conditions. When we assay dynamins GTPase activity under low ionic strength conditions (50mM) we have obtained Kcat values of up to 0.4s-1. We believe that the increase in activity at low ionic strength is due to spontaneous dynamin oligomerisation as has been previously reported6 8 9. Variability in this basal activity, most likely represents variable amounts of spontaneous oligomerisation in different dynamin preparations.
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