Bisphosphorylation of cardiac troponin I modulates the Ca(2+)-dependent binding of myosin subfragment S1 to reconstituted thin filaments.
We have reconstituted thin filaments comprising pyrene-labelled actin (pyr-actin), tropomyosin (Tm) and cardiac troponin (cTn). cTn was isolated in two defined phosphorylation states; completely dephosphorylated on all subunits and with only the cTnI subunit bisphosphorylated. The thin filament was saturated with cTn at a pyr-actin/Tm/cTn ratio of 7:1:1. The calcium-dependent binding of S1 to thin filaments was measured in a stopped-flow spectrophotometer and the dependence of the observed rate constant on [Ca2+] fitted to the Hill equation. The only significant difference between the two phosphorylation states of the filaments was a 0.36 decrease in the pCa50 on bisphosphorylation.
Reiffert
S U
SU
Ruhr-Universität Bochum, Abteilung für Biochemie Supramolekularer Systeme, Germany.
Jaquet
K
K
Heilmeyer
L M
LM
Ritchie
M D
MD
Geeves
M A
MA
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D000199:Actins / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002415:Cats; D007700:Kinetics; D018482:Muscle, Skeletal / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism*; D010766:Phosphorylation; D011721:Pyrenes; D011817:Rabbits; D014335:Tropomyosin / Q000378:metabolism; D014336:Troponin / Q000378:metabolism*; D019210:Troponin I
D000199:Actins; D015879:Myosin Subfragments; D011721:Pyrenes; D014335:Tropomyosin; D014336:Troponin; D019210:Troponin I; D002118:Calcium