| Abstract: | Previous work has indicated that following the rapid adenosine 5'-triphosphate (ATP) induced dissociation of the microtubule-dynein complex, the rate-limiting step in the ATPase cycle is product release Johnson, K. A. (1983) J. Biol. Chem. 258, 13825-13832], which occurs at a rate of approximately 2-6 s-1. In this report we complete the analysis of the ATPase cycle by examining the effect of microtubules on the rate of product release. For these studies we used repolymerized Tetrahymena axonemal microtubules and microtubule-associated protein (MAP) free bovine brain microtubules which were shown to be free of any measureable ATPase activity. Tetrahymena 22S dynein bound to these microtubules predominantly by the ATP-sensitive site and at a rate giving an apparent second-order rate constant of (0.2-1) X 10(6) M-1 s-1, which is 50-fold greater than the rate observed with brain microtubules containing MAPs. ATP induced the rapid dissociation of the microtubule-dynein complex with an apparent second-order rate constant vs. ATP concentration equal to 1.6 X 10(6) M-1 s-1; this value is only slightly lower than that observed in the presence of MAPs. After the ATP-induced dissociation, the dynein reassociated with the microtubules following a lag period due to the time required to hydrolyze the ATP. The duration of the lag time for reassociation decreased with increasing microtubule concentration, suggesting that microtubules increased the rate of ATP turnover. Direct measurements at steady state showed that the specific activity of the dynein increased with increasing microtubule concentration.(ABSTRACT TRUNCATED AT 250 WORDS) |
