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Elevated levels of phosphate enhance myosin driven actin filament velocity under acidic conditions
Author(s) -
Stout Jordan Catherine,
Guha Arunima,
Harkey Jennifer,
Debold Edward Patrick
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.lb671
Subject(s) - myosin , actin , chemistry , biophysics , phosphate , motility , protein filament , acidosis , biochemistry , endocrinology , biology , microbiology and biotechnology
Elevated levels of phosphate (P i ) and decreased pH (i.e. acidosis) are believed to contribute to muscular fatigue by directly inhibiting muscle's molecular motor, myosin. However, the mechanisms of inhibition are not fully understood at a molecular level. We determined the effects of elevated P i (30mM) and low pH (6.5) at saturating ATP (2mM), separately and in combination, on myosin's ability to move actin in an in vitro motility assay (V actin ). Decreasing the pH without added P i significantly (p<0.05) slowed V actin (6.1 ± 0.2 at pH 7.4 vs. 1.6 ± 0.2 um/s at pH 6.5). The addition of P i slightly increased V actin at pH 7.4 (6.1 ± 0.2 at 0mM P i vs. 6.8 ± 0.2 um/s at 30mM P i ), while at pH 6.5, P i increased V actin ~2‐fold (1.6 ± 0.2 at 0mM P i vs. 3.3 ± 0.2 um/s at 30mM P i ). Repeating these experiments at sub‐saturating ATP showed that elevated P i decreased V actin below 1mM ATP at pH 7.4. However, at pH 6.5, elevated P i continued to increase V actin at all measured ATP concentrations (from 100uM to 2mM). These data indicate that the effects of P i on myosin depend on both the pH and the ATP concentration. Since ATP affects the rigor lifetime and pH is believed to affect the ADP‐lifetime, these data imply that P i may be able to rebind to myosin at more than one step in the cross‐bridge cycle. This work was funded by American Heart Association SDG grant (09SDG2260776) to Edward P. Debold