title: Binding of ADP and adenosine 5'-[beta, gamma-imido]triphosphate to insect flight muscle fibrils.
abstract: We have studied the binding of ADP and adenosine 5'-[beta, gamma-imido]triphosphate (AdoPP[NH]P) to insect flight muscle fibrils. We find that 25% of the myosin heads, presumably those which do not interact with actin, bind AdoPP[NH]P with a binding constant greater than 3 X 10(6) M-1, similar to the binding constant of the same compound to the rabbit myosin heads which do not overlap with actin. The remaining heads in insect myofibrils bind AdoPP[NH]P with an association constant of 8 X 10(3) M-1, which is eight times stronger than the affinity of this compound for rabbit myosin heads in overlap with actin. Therefore, in contrast to the situation with rabbit myofibrils where AdoPP[NH]P binds much more weakly than ADP, with insect myofibrils these two adenosine phosphates bind with almost equal affinity. This is consistent with the numerous structural studies on insect flight muscle which were interpreted on the basis that most of the actomyosin sites were saturated with nucleotide at an AdoPP[NH]P concentration of 1 mM.
authors.affiliation: Laboratory of Cell Biology, National Institutes of Health, National Heart, Lung, and Blood Institute, Bethesda.
authors.forename: J A
authors.initials: JA
authors.lastname: Biosca
authors.forename: E
authors.initials: E
authors.lastname: Eisenberg
authors.forename: M C
authors.initials: MC
authors.lastname: Reedy
authors.forename: M K
authors.initials: MK
authors.lastname: Reedy
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives*; D000266:Adenylyl Imidodiphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D005426:Flight, Animal; D007313:Insecta; D009132:Muscles / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D011817:Rabbits
chemical_list: D000266:Adenylyl Imidodiphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009218:Myosins