Vol. 91, Issue 6, 2479-2486, December 2001
Myosin cross bridges in skeletal muscles: "rower"
molecular motors
Y.
Lecarpentier,
D.
Chemla,
J. C.
Pourny,
F.-X.
Blanc, and
C.
Coirault
Service de Physiologie, Université Paris-Sud XI,
Hôpital Bicêtre, Assistance Publique-Hôpitaux de
Paris, 94275 Le Kremlin-Bicêtre; and Laboratoire d'Optique
Appliquée Unité Mixte de Recherche-7639, Centre National de
La Recherche Scientifique, Ecole Nationale Supérieure de
Techniques Avancées-Ecole Polytechnique, Institut National de
la Sante et de la Recherche Médicale, 91761 Palaiseau,
France
Different classes of molecular motors, "rowers" and
"porters," have been proposed to describe the chemomechanical
transduction of energy. Rowers work in large assemblies and
spend a large percentage of time detached from their lattice substrate.
Porters behave in the opposite way. We calculated the number of myosin
II cross bridges (CB) and the probabilities of attached and detached
states in a minimal four-state model in slow (soleus) and fast
(diaphragm) mouse skeletal muscles. In both muscles, we found that the
probability of CB being detached was ~98% and the number of working
CB was higher than 109/mm2. We concluded that
muscular myosin II motors were classified in the category of rowers.
Moreover, attachment time was higher than time stroke and time for ADP
release. The duration of the transition from detached to attached
states represented the rate-limiting step of the overall attached time.
Thus diaphragm and soleus myosins belong to subtype 1 rowers.
duty ratio; attached and detached cross-bridge probabilities
