title: Binding of ADP and 5'-adenylyl imidodiphosphate to rabbit muscle myofibrils.
abstract: The binding of [3H]ADP and [3H]adenyl-5'-yl-imidodiphosphate ([3H]AMP-PNP) to rabbit skeletal myofibrils was measured at 25 and 7 degrees C, mu = 0.12 M, using [14C]mannitol as a volume marker. We found that ADP bound to myosin heads in overlap with a binding constant of about 10(4) M-1, similar to the value we previously obtained in vitro with acto.S-1. The binding of AMP-PNP to myosin heads was measured both in and out of overlap. The affinity of AMP-PNP to the heads out of overlap was similar to that obtained in vitro with S-1 alone. The binding of AMP-PNP to the myosin heads in overlap was much weaker. We could fit these data with a binding constant of about 1 x 10(3) M-1, assuming a single population of cross-bridges and 1 mol of AMP-PNP bound per mol of myosin head. This value was reduced by a factor of 2 when we corrected for nonspecific binding. It was also possible to fit the data assuming two equal populations of cross-bridges with one of the populations binding AMP-PNP about 5-fold more strongly than the other population. Therefore, for at least half of the cross-bridges in overlap, the binding of AMP-PNP is almost as weak as the value of 3 x 10(2) M-1 we previously measured for the acto.S-1 complex in vitro (Biosca, J. A., Greene, L. E., and Eisenberg, E. (1986) J. Biol. Chem. 261, 9793-9800).
authors.affiliation: Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
authors.forename: J A
authors.initials: JA
authors.lastname: Biosca
authors.forename: L E
authors.initials: LE
authors.lastname: Greene
authors.forename: E
authors.initials: E
authors.lastname: Eisenberg
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives*; D000266:Adenylyl Imidodiphosphate / Q000378:metabolism*; D000818:Animals; D007700:Kinetics; D009132:Muscles / Q000378:metabolism* / Q000502:physiology; D009210:Myofibrils / Q000378:metabolism* / Q000502:physiology; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D011817:Rabbits
chemical_list: D015879:Myosin Subfragments; D010446:Peptide Fragments; D000266:Adenylyl Imidodiphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009218:Myosins