Premium
Characterization of the cross‐bridge force‐generating step using inorganic phosphate and BDM in myofibrils from rabbit skeletal muscles
Author(s) -
Tesi C.,
Colomo F.,
Piroddi N.,
Poggesi C.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.013418
Subject(s) - isometric exercise , myofibril , chemistry , isomerization , soleus muscle , biophysics , skeletal muscle , phosphate , muscle contraction , anatomy , stereochemistry , biochemistry , medicine , biology , catalysis
The inhibitory effects of inorganic phosphate (P i ) on isometric force in striated muscle suggest that in the ATPase reaction P i release is coupled to force generation. Whether P i release and the power stroke are synchronous events or force is generated by an isomerization of the quaternary complex of actomyosin and ATPase products (AM.ADP.P i ) prior to the following release of P i is still controversial. Examination of the dependence of isometric force on [P i ] in rabbit fast (psoas; 5‐15 °C) and slow (soleus; 15‐20 °C) myofibrils was used to test the two‐step hypothesis of force generation and P i release. Hyperbolic fits of force‐[P i ] relations obtained in fast and slow myofibrils at 15 °C produced an apparent asymptote as [P i ]∞ of 0.07 and 0.44 maximal isometric force (i.e. force in the absence of P i ) in psoas and soleus myofibrils, respectively, with an apparent K d of 4.3 m m in both. In each muscle type, the force‐[P i ] relation was independent of temperature. However, 2,3‐butanedione 2‐monoxime (BDM) decreased the apparent asymptote of force in both muscle types, as expected from its inhibition of the force‐generating isomerization. These data lend strong support to models of cross‐bridge action in which force is produced by an isomerization of the AM.ADP.P i complex immediately preceding the P i release step.