Open AccessCatalytic consequences of oligomeric organization: kinetic evidence for "tethered" acto-heavy meromyosin at low ATP concentrations.
Author(s) -
David D. Hackney,
Pancreas Clark
Publication year - 1984
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.81.17.5345
Subject(s) - heavy meromyosin , atp hydrolysis , actin , atpase , chemistry , biochemistry , myosin , biophysics , adenosine triphosphate , biology , enzyme
The influence of the supramolecular organization of myosin on its ATPase activity was investigated at a range of ATP concentrations, using as a model system subfragment 1 (S1) and heavy meromyosin (HMM), which are respectively monomeric and dimeric proteolytic fragments of myosin. At low ATP levels in the presence of a molar excess of actin, dimeric HMM showed an increased rate of ATP hydrolysis relative to that for monomeric S1. This increased ATPase for HMM was inhibited by high concentrations of ATP, which reduced the acto-HMM ATPase rate to the lower level of acto-S1. This observation is consistent with the rapid ATP hydrolysis of acto-HMM at low ATP being due to rapid product release from a "tethered" acto-HMM species, which has product bound to one head group while the other head group remains bound to actin. At high concentrations of ATP, ATP binds to both head groups, resulting in net dissociation of HMM from actin. This model is supported by 18O exchange data. Acto-HMM hydrolyzed ATP with extensive exchange of water oxygens into Pi at high ATP levels, but not at low ATP levels. Acto-S1 exhibited extensive exchange at both high and low ATP levels. This result is consistent with rapid product release from a tethered acto-HMM intermediate at low ATP.