ISSN:
1573-2657
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract The structure of truncated, recombinant Dictyostelium myosin motor domain complexed with Mg · ADP and slowly dissociating analogues of Pi has previously been characterized as two main states (S1-MgADP plus BeF vs. AlF 2 − or Vi). The BeF bound state is thought to mimic the weak actin-binding M · ATP complex, while the states with AlF 2 − or Vi bound mimic the M · ADP · Pi state. While the effects of AlF 2 − and Vi on fibre mechanics have been previously described (Chase etal., 1994, 1993), the effects of BeF have not been characterized in detail. At pCa 4.5 (12°C), we measured (i) steady-state isometric tension, (ii) stiffness (KS; 1 kHz sinusoids), and (iii)unloaded shortening velocity (Vu; slack test) in single skinned muscle fibres from rabbit psoas. Results were compared when tension was inhibited with either BeF or 2,3-butanedione-monoxime (BDM) or modulated by altering myoplasmic [Ca2+]. With 3 mM total fluoride, 1 mM BeF inhibited both tension and KS by ∼ 50% (compared to 7–10 mM BDM and 50–100 μM AlF 2 − ). Increasing [BeF] to 10 mM further reduced tension to ∼ 15% P0, but had little further effect on KS; with BDM and altered [Ca2+], KS scaled more proportionately with tension. Inhibition of tension and KS by BeF was more rapidly reversible, compared with slow recovery from tension inhibition with AlF 2 − or Vi. Vu exhibited a complex dependence on [BeF], being relatively unaffected by concentrations ≤1 mM, and becoming inhibited steeply for [BeF] above this level. With BDM, Vu co-varied more directly with force. Our results suggest that BeF may induce a different cross-bridge state in fibres than do AlF 2 − or Vi, but all three analogues of Pi form complexes that mimic crossbridge states that follow ATP hydrolysis.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1005594001334
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