Biomaterial Database

Interdependence of factors affecting the actin-activated ATPase activity of myosin II from Acanthamoeba castellanii. 1984

J Kuznicki, and E D Korn

Acanthamoeba myosin II can be phosphorylated at three serine residues near the C terminus of each heavy chain. Deophosphorylated myosin II has the highest actin-activated ATPase activity. In this paper, we report the interdependent effects of phosphorylation, Mg2+, Ca2+, temperature, pH, and KCl on the acti-activated ATPase activity. With increasing level of phosphorylation, the actin-activated ATPase activity decreases and the optimal concentration of Mg2+ increases. Lowering the temperature of assay from 35 to 20 degrees C reduces the specific activity of dephosphorylated myosin II and increases the optimal Mg2+ concentration. Lowering the pH from 7.7 to 6.4 decreases the optimal Mg2+ concentration for dephosphorylated myosin II but has no effect on its specific activity. Below pH 6.4, the activity of dephosphorylated myosin is decreased. Phosphorylated myosin II, on the other hand, has no actin-activated ATPase activity at pH 6.4 and above, irrespective of the Mg2+ concentration, but has significant activity at lower pH with a maximum at pH 6.0-6.1 in 1 mM Mg2+. Dephosphorylated myosin II requires Mg2+ for actin-activated ATPase activity under all conditions, but Ca2+ can substitute for some of the Mg2+ at pH 7.0. Partial inhibition of dephosphorylated myosin II by 10-15 mM KCl can be overcome by increasing the Mg2+ concentration but the enzyme is 60% inhibited at 25 mM KCl irrespective of the Mg2+ concentration. The actin-activated ATPase activity of maximally dephosphorylated myosin II is as high at pH 6.4, 1 mM Mg2+, and 30 degrees C, which may be near physiological conditions, as at pH 7, 4 mM Mg2+, and 35 degrees C, the assay conditions commonly used previously. Under both conditions, maximally phosphorylated myosin II is inactive. The interdependence of all these effectors emphasizes the ned to employ multiple incubation conditions in assessing the actin-activated ATPase activities of myosins from all sources.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008274	Magnesium	A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.
D009218	Myosins	A diverse superfamily of proteins that function as translocating proteins. They share the common characteristics of being able to bind ACTINS and hydrolyze MgATP. Myosins generally consist of heavy chains which are involved in locomotion, and light chains which are involved in regulation. Within the structure of myosin heavy chain are three domains: the head, the neck and the tail. The head region of the heavy chain contains the actin binding domain and MgATPase domain which provides energy for locomotion. The neck region is involved in binding the light-chains. The tail region provides the anchoring point that maintains the position of the heavy chain. The superfamily of myosins is organized into structural classes based upon the type and arrangement of the subunits they contain.	Myosin ATPase,ATPase, Actin-Activated,ATPase, Actomyosin,ATPase, Myosin,Actin-Activated ATPase,Actomyosin ATPase,Actomyosin Adenosinetriphosphatase,Adenosine Triphosphatase, Myosin,Adenosinetriphosphatase, Actomyosin,Adenosinetriphosphatase, Myosin,Myosin,Myosin Adenosinetriphosphatase,ATPase, Actin Activated,Actin Activated ATPase,Myosin Adenosine Triphosphatase
D010766	Phosphorylation	The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety.	Phosphorylations
D002413	Cations, Divalent	Positively charged atoms, radicals or groups of atoms with a valence of plus 2, which travel to the cathode or negative pole during electrolysis.	Divalent Cations
D006863	Hydrogen-Ion Concentration	The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH	pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D000251	Adenosine Triphosphatases	A group of enzymes which catalyze the hydrolysis of ATP. The hydrolysis reaction is usually coupled with another function such as transporting Ca(2+) across a membrane. These enzymes may be dependent on Ca(2+), Mg(2+), anions, H+, or DNA.	ATPases,Adenosinetriphosphatase,ATPase,ATPase, DNA-Dependent,Adenosine Triphosphatase,DNA-Dependent ATPase,DNA-Dependent Adenosinetriphosphatases,ATPase, DNA Dependent,Adenosinetriphosphatases, DNA-Dependent,DNA Dependent ATPase,DNA Dependent Adenosinetriphosphatases,Triphosphatase, Adenosine
D000656	Amoeba	A genus of ameboid protozoa. Characteristics include a vesicular nucleus and the formation of several PSEUDOPODIA, one of which is dominant at a given time. Reproduction occurs asexually by binary fission.	Ameba
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013696	Temperature	The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.	Temperatures