title: The dependence of isometric tension, isometric ATPase activity, and shortening velocity of limulus muscle on the MgATP concentration.
abstract: The dependence of the isometric tension, the velocity of unloaded shortening, and the steady-state rate of MgATP hydrolysis on the MgATP concentration (range 0.01-5 mM MgATP) was studied in Ca-activated skinned Limulus muscle fibers. With increasing MgATP concentration the isometric tension increased to a peak at approximately 0.1 mM, and slightly decreased in the range up to 5 mM MgATP. The velocity of unloaded shortening depended on the MgATP concentration roughly according to the Michaelis-Menten law of saturation kinetics with a Michaelis-Menten constant Kv = 95 microM and a maximum shortening velocity of 0.07 muscle lengths s-1; the detachment rate of the cross-bridges during unloaded shortening was 24 s-1. The rate of MgATP splitting also depended hyperbolically on the MgATP concentration with a Michaelis-Menten constant Ka = 129 microM and a maximum turnover frequency of 0.5-1 s-1. The results are discussed in terms of a cross-bridge model based on a biochemical scheme of ATP hydrolysis by actin and myosin in solution.
authors.affiliation: Abteilung für Allgemeine Physiologie, Universität Ulm, Federal Republic of Germany.
authors.forename: S
authors.initials: S
authors.lastname: Pferrer
authors.forename: R
authors.initials: R
authors.lastname: Kulik
authors.forename: T
authors.initials: T
authors.lastname: Hiller
authors.forename: H J
authors.initials: HJ
authors.lastname: Kuhn
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D006737:Horseshoe Crabs; D007537:Isometric Contraction; D007700:Kinetics; D009119:Muscle Contraction; D009132:Muscles / Q000201:enzymology / Q000502:physiology*
chemical_list: D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases