Pl. Tuma et Ca. Collins, ACTIVATION OF DYNAMIN GTPASE IS A RESULT OF POSITIVE COOPERATIVITY, The Journal of biological chemistry, 269(49), 1994, pp. 30842-30847
Dynamin is a GTP-binding protein thought to be involved in the early s
tages of endocytosis. Presently, it is not known how dynamin GTP bindi
ng and hydrolysis are related to its role in this process. We previous
ly characterized the ability of acidic phospholipid vesicles and micro
tubules to strongly stimulate the GTPase activity of purified brain dy
namin. In a further analysis of dynamin enzymatic properties, we have
found that the increase of dynamin GTP hydrolysis in the presence of a
ctivating agent depends on enzyme concentration. At low enzyme concent
ration, Little or no activation is observed. Plots of dynamin GTPase a
ctivity with increasing enzyme concentration in the presence of either
activating agent are strongly sigmoidal, indicating that positive coo
perativity is responsible for the increased activity observed. A Hill
coefficient of 2.3 was determined, implying that at least two dynamin
molecules associate for maximal GTPase activity. No cooperative effect
s in GTP binding were observed. Linear transformation of reaction velo
city versus enzyme concentration data indicate an apparent II, for dyn
amin-dynamin interactions of 37 nM, which is significantly lower than
the physiological concentration of dynamin in brain. These results sug
gest that cooperative interactions between dynamin molecules are respo
nsible for the apparent activation of GTPase observed and are likely i
nvolved in dynamin function in vivo.