Journal article
Elementary Steps of the Cross-Bridge Cycle in Fast-Twitch Fiber Types from Rabbit Skeletal Muscles
Biophysical journal, Vol.89(5), pp.3248-3260
11/2005
DOI: 10.1529/biophysj.104.056614
PMCID: PMC1366820
PMID: 16143633
Abstract
To understand the molecular mechanism underlying the diversity of mammalian skeletal muscle fibers, the elementary steps of the cross-bridge cycle were investigated in three fast-twitch fiber types from rabbit limb muscles. Skinned fibers were maximally Ca2+-activated at 20°C and the effects of MgATP, phosphate (P, Pi), and MgADP were studied on three exponential processes by sinusoidal analysis. The fiber types (IIA, IID, and IIB) were determined by analyzing the myosin heavy-chain isoforms after mechanical experiments using high-resolution SDS-PAGE. The results were consistent with the following cross-bridge scheme: ▪ where A is actin, M is myosin, D is MgADP, and S is MgATP. All states except for those in brackets are strongly bound states. All rate constants of elementary steps (k2, 198–526s−1; k−2, 51–328s−1; k4, 13.6–143s−1; k−4, 13.6–81s−1) were progressively larger in the order of type IIA, type IID, and type IIB fibers. The rate constants of a transition from a weakly bound state to a strongly bound state (k−2, k4) varied more among fiber types than their reversals (k2, k−4). The equilibrium constants K1 (MgATP affinity) and K2 (=k2/k−2, ATP isomerization) were progressively less in the order IIA, IID, and IIB. K4 (=k4/k−4, force generation) and K5 (Pi affinity) were larger in IIB than IIA and IID fibers. K1 showed the largest variation indicating that the myosin head binds MgATP more tightly in the order IIA (8.7mM−1), IID (4.9mM−1), and IIB (0.84mM−1). Similarly, the MgADP affinity (K0) was larger in type IID fibers than in type IIB fibers.
Details
- Title: Subtitle
- Elementary Steps of the Cross-Bridge Cycle in Fast-Twitch Fiber Types from Rabbit Skeletal Muscles
- Creators
- Stefan Galler - Department of Cell Biology, Faculty of Natural Sciences, University of Salzburg, A-5020 Salzburg, AustriaBrant Gang Wang - Department of Anatomy and Cell Biology, College of Medicine, University of Iowa, Iowa City, Iowa 52242 USAMasataka Kawai - Department of Anatomy and Cell Biology, College of Medicine, University of Iowa, Iowa City, Iowa 52242 USA
- Resource Type
- Journal article
- Publication Details
- Biophysical journal, Vol.89(5), pp.3248-3260
- Publisher
- Elsevier Inc
- DOI
- 10.1529/biophysj.104.056614
- PMID
- 16143633
- PMCID
- PMC1366820
- ISSN
- 0006-3495
- eISSN
- 1542-0086
- Language
- English
- Date published
- 11/2005
- Academic Unit
- Anatomy and Cell Biology; Internal Medicine
- Record Identifier
- 9984025688502771
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