title: Kinetic characterization of brush border myosin-I ATPase.
abstract: Brush border myosin-I (BBM-I) is a single-headed unconventional myosin found in the microvilli of intestinal epithelial cells. We used stopped-flow kinetic analysis to measure the rate and equilibrium constants for several steps in the BBM-I ATPase cycle. We determined the rates for ATP binding to BBM-I and brush border actomyosin-I (actoBBM-I), the rate of actoBBM-I dissociation by ATP, and the rates for the steps in ADP dissociation from actoBBM-I. The rate and equilibrium constants for several of the steps in the actoBBM-I ATPase are significantly different from those of other members of the myosin superfamily. Most notably, dissociation of the actoBBM-I complex by ATP and release of ADP from actoBBM-I are both very slow. The slow rates of these steps may play a role in lengthening the time spent in force-generating states and in limiting the maximal rate of BBM-I motility. In addition, release of ADP from the actoBBM-I complex occurs in at least two steps. This study provides evidence for a member of the myosin superfamily with markedly divergent kinetic behavior.
authors.affiliation: Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Jontes
authors.forename: R A
authors.initials: RA
authors.lastname: Milligan
authors.forename: T D
authors.initials: TD
authors.lastname: Pollard
authors.forename: E M
authors.initials: EM
authors.lastname: Ostap
mesh_terms: D007700:Kinetics; D009218:Myosins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D009218:Myosins