SOME CHARACTERISTICS OF ATPASE ACTIVITY IN A BRAIN MICROTUBULE PROTEIN PREPARATION

Abstract— The Mg‐ and Ca‐ATPase activities in a brain tubulin preparation have been measured. The activity of the microtubule protein (MTP) preparation was optimal, 3‐4.5 nmol Pi/mg protein/min, at pH 8.0 in the presence of 1‐2 mm‐Mg2+ or Ca2+, with a half maximal stimulation at about 0.3 mm concentration of either of the divalent ions. Phosphocellulose (PC) purified tubulin exhibited no or very low activity (0‐2 nmol Pi/mg protein/min). The majority of ATPase activity was found in the microtubule associated proteins (MAP) fraction. It was stimulated by Mg2+ and Ca2+, inhibited by NaF or high ionic strength but unaffected by vanadate at 10−4m. In decreasing order of effectiveness ATP, GTP, UTP, CTP and ADP were hydrolyzed. p‐Npp was a poor substrate. Vmax values for Mg‐ and Ca‐ATPase activities were about 15 and 10 nmol Pi/mg protein/min, respectively with a Km value of about 25 μm. However, double reciprocal plots disclosed more complicated kinetics, which were not fully resolved. The activity was largely confined to 30‐36S material (i.e.‘rings’and 'spirals'). The protein responsible for the ATPase activity is possibly the smaller one of the two (or three) high molecular weight (HMW) proteins of mol wt over 200,000. There are similarities between this enzyme and both flagellar dynein and myosin. However, the present ATPase differs from myosin in several important aspects (i.e. ionic requirements). Furthermore, no peptides of the myosin type were found upon electrophoretic analysis of the MAP fraction. Copyright © 1979, Wiley Blackwell. All rights reserved