+ Site Statistics
References:
52,654,530
Abstracts:
29,560,856
PMIDs:
28,072,755
+ Search Articles
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ PDF Full Text
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn

+ Translate
+ Recently Requested

The effect of partial extraction of troponin C on the elementary steps of the cross-bridge cycle in rabbit psoas muscle fibers



The effect of partial extraction of troponin C on the elementary steps of the cross-bridge cycle in rabbit psoas muscle fibers



Biophysical Journal 71(5): 2759-2773



The elementary steps of the cross-bridge cycle in which troponin C (TnC) was partially extracted were investigated by sinusoidal analysis in rabbit psoas muscle fibers. The effects of MgATP and phosphate on the rate constants of exponential processes were studied at 200 mM ionic strength, pCa 4.20, pH 7.00, and at 20 degrees C. The results were analyzed with the following cross-bridge scheme: [formula: see text] where A is actin, M is myosin, S is MgATP, D is MgADP, and P is phosphate (Pi). When TnC was extracted so that the average remaining tension was 11% (range 8-15%), K1 (MgATP association constant) increased to 7x, k2 (rate constant of cross-bridge detachment) increased to 1.55x, k-2 (reversal of detachment) decreased to 0.27x, and K2 (= k2/k-2: equilibrium constant of cross-bridge detachment) increased to 6.6x, k4 (rate constant of force generation) decreased to 0.4x, k-4 (reversal of force generation) increased to 2x, K4 (= k4/k-4) decreased to 0.17x, and K5 (Pi association constant) did not change. The activation factor alpha, which represents the fraction of cross-bridges participating in the cycling, decreased from 1 to 0.14 with TnC extraction. The fact that K1 increased with TnC extraction implies that the condition of the thin filament modifies the contour of the substrate binding site on the myosin head and is consistent with the Fenn effect. The fact that alpha decreased to 0.14 is consistent with the steric blocking mechanism (recruitment hypothesis) and indicates that some of the cross-bridges disappear from the active cycling pool. The fact that the equilibrium constants changed is consistent with the cooperative activation mechanism (graded activation hypothesis) among thin-filament regulatory units that consist of troponin (TnC, Tnl, TnT), tropomyosin, and seven actin molecules, and possibly include cross-bridges.

(PDF emailed within 0-6 h: $19.90)

Accession: 009565291

Download citation: RISBibTeXText

PMID: 8913613

DOI: 10.1016/S0006-3495(96)79469-9



Related references

Effect of partial extraction of troponin C on elementary steps of the cross-bridge cycle in skinned rabbit psoas muscle fibers. Biophysical Journal 66(2 PART 2): A303, 1994

Effect of in-series thin filament compliance on the elementary steps of the cross-bridge cycle in skinned rabbit psoas muscle fibers. Biophysical Journal 72(2 PART 2): A281, 1997

The effect of temperature on the elementary steps of the cross bridge cycle in rabbit psoas fibers. Biophysical Journal 61(2 PART 2): A267, 1992

Temperature effect on elementary steps of the cross-bridge cycle in rabbit soleus muscle fibers. Biophysical Journal 68(2 PART 2): A17, 1995

Elementary steps of the cross-bridge cycle in rabbit soleus muscle fibers. Biophysical Journal 66(2 PART 2): A304, 1994

BDM affects nucleotide binding and force generation steps of the cross-bridge cycle in rabbit psoas muscle fibers. American Journal of Physiology 266(2 Pt 1): C437-C447, 1994

Elementary steps of the cross-bridge cycle in rabbit soleus fast-twitch muscle fibers. Biophysical Journal 72(2 PART 2): A127, 1997

The effect of the lattice spacing change on cross-bridge kinetics in chemically skinned rabbit psoas muscle fibers. II. Elementary steps affected by the spacing change. Biophysical Journal 64(1): 197-210, 1993

Temperature and phosphate effects on the elementary steps of the cross-bridge cycle in rabbit soleus slow-twitch muscle fibers. Biophysical Journal 70(2 PART 2): A265, 1996

BDM affects nucleotide binding steps of the cross-bridge cycle in rabbit psoas fibers. Biophysical Journal 64(2 PART 2): A118, 1993

The cross-bridge cycle in muscle. Mechanical, biochemical, and structural studies on single skinned rabbit psoas fibers to characterize cross-bridge kinetics in muscle for correlation with the actomyosin-ATPase in solution. Basic Research in Cardiology 81 Suppl 1: 1-15, 1986

Effect of temperature on elementary steps of the cross-bridge cycle in rabbit soleus slow-twitch muscle fibres. Journal of Physiology (Cambridge) 531(1): 219-234, February 15th, 2001

Kinetic and thermodynamic studies of the cross-bridge cycle in rabbit psoas muscle fibers. Biophysical Journal 67(4): 1655-1668, 1994

The effects of partial extraction of tnc troponin subunit on the tension calcium concentration relation in skinned single fibers from rabbit psoas muscle. Biophysical Journal 45(2 PART 2): 344A, 1984