Biomaterial Database

Filamentous smooth muscle myosin is regulated by phosphorylation. 1989

K M Trybus

Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254-9110.

The enzymatic activity of filamentous dephosphorylated smooth muscle myosin has been difficult to determine because the polymer disassembles to the folded conformation in the presence of MgATP. Monoclonal antirod antibodies were used here to "fix" dephosphorylated myosin in the filamentous state. The steady-state actin-activated ATPase of phosphorylated filaments was 30-100-fold higher than that of antibody-stabilized dephosphorylated filaments, suggesting that phosphorylation can activate ATPase activity independent of changes in assembly. The degree of regulation may exceed 100-fold, because steady-state measurements slightly overestimate the rate of product release from dephosphorylated filaments. Single-turnover experiments in the absence of actin showed that although dephosphorylated folded myosin released products at the low rate of 0.0005 s-1 (Cross, R. A., K. E. Cross, A. Sobieszek. 1986. EMBO [Eur. Mol. Biol. Organ.] J. 5:2637-2641) the rate of product release from dephosphorylated filaments was only 3-12-fold higher, depending on the ionic strength. The addition of actin did not increase this rate to any appreciable extent. Dephosphorylated filaments and dephosphorylated heavy meromyosin (Sellers, J. R. 1985. J. Biol. Chem. 260:15815-15819) thus have similar low rates of phosphate release both in the presence and absence of actin. These results show that light chain phosphorylation alone, without invoking other mechanisms, is an effective switch for regulating the activity of smooth muscle myosin filaments.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008841	Actin Cytoskeleton	Fibers composed of MICROFILAMENT PROTEINS, which are predominately ACTIN. They are the smallest of the cytoskeletal filaments.	Actin Filaments,Microfilaments,Actin Microfilaments,Actin Cytoskeletons,Actin Filament,Actin Microfilament,Cytoskeleton, Actin,Cytoskeletons, Actin,Filament, Actin,Filaments, Actin,Microfilament,Microfilament, Actin,Microfilaments, Actin
D008854	Microscopy, Electron	Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.	Electron Microscopy
D009130	Muscle, Smooth	Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant. (From Stedman, 25th ed)	Muscle, Involuntary,Smooth Muscle,Involuntary Muscle,Involuntary Muscles,Muscles, Involuntary,Muscles, Smooth,Smooth Muscles
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
D010761	Phosphorus Radioisotopes	Unstable isotopes of phosphorus that decay or disintegrate emitting radiation. P atoms with atomic weights 28-34 except 31 are radioactive phosphorus isotopes.	Radioisotopes, Phosphorus
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
D004789	Enzyme Activation	Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1, activation by ions (activators); 2, activation by cofactors (coenzymes); and 3, conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme.	Activation, Enzyme,Activations, Enzyme,Enzyme Activations
D005895	Gizzard, Avian	The posterior portion of the avian stomach located between the PROVENTRICULUS and INTESTINE. It consists of a thick muscular wall and small stones (gastroliths) that function to mechanically grind SEEDS and other ingested objects.	Gizzard,Ventriculus,Avian Gizzard,Avian Gizzards,Gizzards,Gizzards, Avian
D000199	Actins	Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or F-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or G-actin. In conjunction with MYOSINS, actin is responsible for the contraction and relaxation of muscle.	F-Actin,G-Actin,Actin,Isoactin,N-Actin,alpha-Actin,alpha-Isoactin,beta-Actin,gamma-Actin,F Actin,G Actin,N Actin,alpha Actin,alpha Isoactin,beta Actin,gamma Actin