Effect of Ca2+ on weak cross-bridge interaction with actin in the presence of adenosine 5'-[gamma-thio]triphosphate).
In the presence of the nucleotide analog adenosine 5'-[gamma-thio]triphosphate (ATP[gamma S]), effects of Ca2+ on stiffness and equatorial x-ray diffraction patterns of single skinned fibers of the rabbit psoas muscle were studied. It is shown that cross-bridges in the presence of ATP[gamma S] have properties of the weak-binding states of the ATP hydrolysis cycle. Raising the Ca2+ concentration up to pCa 4.5 has little effect on actin affinity of cross-bridges in the presence of ATP[gamma S]. However, the rate constants for cross-bridge dissociation and reassociation from and to actin are reduced by about 2 orders of magnitude. In addition, nucleotide affinity of the cross-bridge is much smaller at high Ca2+ concentrations. Implications for interpretation of fiber stiffness recorded during isotonic shortening and the rising phase of a tetanus are discussed.
Kraft
T
T
Department of General Physiology, University of Ulm, Federal Republic of Germany.
Yu
L C
LC
Kuhn
H J
HJ
Brenner
B
B
D000199:Actins / Q000378:metabolism*; D000205:Actomyosin / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D009038:Motion; D009119:Muscle Contraction; D011485:Protein Binding; D011817:Rabbits
D000199:Actins; C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; D000205:Actomyosin; D002118:Calcium