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          Institute: MPI für medizinische Forschung     Collection: Abteilung Biophysik     Display Documents



ID: 22540.0, MPI für medizinische Forschung / Abteilung Biophysik
X-Ray Diffraction Indicates That Active Cross-Bridges Bind to Actin Target Zones in Insect Flight Muscle
Translation of Title:X-Ray Diffraction Indicates That Active Cross-Bridges Bind to Actin Target Zones in Insect Flight Muscle
Authors:Tregear, Richard T.; Edwards, Robert J.; Irving, T. C.; Poole, Katrina J. V.; Reedy, Michael K.; Schmitz, H.; Towns-Andrews, E.; Reedy, Michael K.
Language:English
Date of Publication (YYYY-MM-DD):1998-03
Title of Journal:Biophysical Journal
Journal Abbrev.:Biophys. J.
Volume:74
Issue / Number:3
Start Page:1439
End Page:1451
Review Status:Peer-review
Audience:Experts Only
Intended Educational Use:No
Abstract / Description:We report the first time-resolved study of the two-dimensional x-ray diffraction pattern during active contraction in insect flight muscle (IFM). Activation of demembranated Lethocerus IFM was triggered by 1.5-2.5% step stretches (risetime 10 ms; held for 1.5 s) giving delayed active tension that peaked at 100-200 ms. Bundles of 8-12 fibers were stretch-activated on SRS synchrotron x-ray beamline 16.1, and time-resolved changes in diffraction were monitored with a SRS 2-D multiwire detector. As active tension rose, the 14.5- and 7.2-nm meridionals fell, the first row line dropped at the 38.7 nm layer line while gaining a new peak at 19.3 nm, and three outer peaks on the 38.7-nm layer line rose. The first row line changes suggest restricted binding of active myosin heads to the helically preferred region in each actin target zone, where, in rigor, two-headed lead bridges bind, midway between troponin bulges that repeat every 38.7 nm. Halving this troponin repeat by binding of single active heads explains the intensity rise at 19.3 nm being coupled to a loss at 38.7 nm. The meridional changes signal movement of at least 30% of all myosin heads away from their axially ordered positions on the myosin helix. The 38.7- and 19.3-nm layer line changes signal stereoselective attachment of 7-23% of the myosin heads to the actin helix, although with too little ordering at 6-nm resolution to affect the 5.9-nm actin layer line. We conclude that stretch-activated tension of IFM is produced by cross-bridges that bind to rigors lead-bridge target zones, comprising 1/3 of the 75-80% that attach in rigor.
External Publication Status:published
Document Type:Article
Communicated by:Wulf Kaiser
Affiliations:MPI für medizinische Forschung/Abteilung Biophysik/
Identifiers:URI:http://www.biophysj.org/cgi/content/full/74/3/1439 [Full text]
URI:http://www.biophysj.org/cgi/content/abstract/74/3/... [Abstract]
URI:http://www.biophysj.org/cgi/reprint/74/3/1439 [Fulltext PDF]
ISSN:0006-3495/98/03/1439/13 $2.00
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