Presence of two distinct adenosine triphosphatase activities in bovine brain microtubules

Abstract

Axonal transport in neuronal tissues is an energy-dependent process requiring the hydrolysis of ATP [l-3], and it has been assumed that a dynein-like ATPase may be associated structurally with brain microtubules. Although there have been several reports which point to the presence of an ATPase activity in preparations of brain microtubules [4-91, it was not certain whether these ATPases were specifically associated with any of the components of microtubules. An ATPase activity is present in the fraction of microtubule-associated proteins (MAPS) from rat brain and is stimulated by the addition of purified 6 S tubulin in the presence of Ca2+ [lo]. The dependency on tubulin of the ATPase activity suggested its structural and functional association with microtubules. Here on further purification of the ATPase activity from the MAPS fraction of bovine brain microtubules, 2 distinct ATPases are separated, designated ATPase ‘I’ and ‘II’. ATPase I is of relatively low Mr (33 000) and dependent on added tubulin in the presence of Ca2+. On the other hand, ATPase II has a larger size and appears to be associated with membrane vesicles. It is observed under electron microscopy as membrane vesicles containing knob-like structures reminiscent of H+-pump ATPases. A preliminary account of this paper appeared in [ 111.