Myosin isolation

Myosin ATPase Myosin isolated from muscle by John Edsall Alexander von Muralt (1930s) 13.8V... 

Myosins isolated from various frozen stored fish muscles had slightly lower ATPase activity than those from fresh muscles (94, 95). A decrease in ATPase activity was found also with isolated carp myosin when stored at -20°C (82) the rate of decrease was faster than with actomyosin isolated from the same fish. As with actomyosin, the decrease in ATPase activity was preceded by a temporary rise in activity M50% the pre-freezing value). 

ATPase. Myosins isolated from various frozen-stored fish muscles exhibit specific activities for ATPase that are slightly lower than the specific activities of myosin from fresh muscles (73,74). The decline of ATPase activity also occurs with myosin isolated from carp, when storage is conducted at — 20°C (64). Like carp actomyosin, the decline is preceded by a temporary rise in activity. 

Additional studies have been conducted on frozen samples of acto-myosin isolated from carp. Actomyosin was either suspended in 0.05M KC1 or dissolved in 0.6M KC1. These studies showed that triphosphate is more cryoprotective than pyrophosphate when actomyosin is suspended in 0.05M KC1, whereas both chemicals are ineffective when actomyosin is dissolved in 0.6M KC1. Orthophosphate was ineffective in both situations (52). 

Chaussepied, P. Kasprzak, A.A. (1989). Isolation and characterization of the G-actin-myosin head complex. Namre 342,950-953. 

Pollard, T.D. Kom, E.D. (1973). Acanthamoeba myosin 1. Isolation form Acanthamoeba castellani of an enzyme similar to muscle myosin. J. Biol. Chem. 248,4682-4690. 

Adams, R.J.. Pollard, T.D. (1986). Propulsion of organelles isolated from Acanthamoeba along actin filaments by myosin-1. Nature 322, 754-756. 

The general picture of muscle contraction in the heart resembles that of skeletal muscle. Cardiac muscle, like skeletal muscle, is striated and uses the actin-myosin-tropomyosin-troponin system described above. Unlike skeletal muscle, cardiac muscle exhibits intrinsic rhyth-micity, and individual myocytes communicate with each other because of its syncytial nature. The T tubular system is more developed in cardiac muscle, whereas the sarcoplasmic reticulum is less extensive and consequently the intracellular supply of Ca for contraction is less. Cardiac muscle thus relies on extracellular Ca for contraction if isolated cardiac muscle is deprived of Ca, it ceases to beat within approximately 1 minute, whereas skeletal muscle can continue to contract without an extraceUular source of Ca +. Cyclic AMP plays a more prominent role in cardiac than in skeletal muscle. It modulates intracellular levels of Ca through the activation of protein kinases these enzymes phosphorylate various transport proteins in the sarcolemma and sarcoplasmic reticulum and also in the troponin-tropomyosin regulatory complex, affecting intracellular levels of Ca or responses to it. There is a rough correlation between the phosphorylation of Tpl and the increased contraction of cardiac muscle induced by catecholamines. This may account for the inotropic effects (increased contractility) of P-adrenergic compounds on the heart. Some differences among skeletal, cardiac, and smooth muscle are summarized in... 

It is not proposed to include the better known polysaccharides or the plant gums in the group because they can be conveniently classified separately. It must be pointed out, however, that some of these may occur naturally in firm combination with protein as instanced by the shock effect observed when solutions of crude inulin are injected into animals and by the reported isolation of desmoglycogen4 and glycogen combined with myosin.6... 

Fairweather, D. et al., Wild isolates of murine cytomegalovirus induce myocarditis and antibodies that cross-react with virus and cardiac myosin, Immunology, 94, 263, 1998. 

Simon H-G, Oppenheimer S. 1996. Advanced mRNA differential display isolation of a new differentially regulated myosin heavy chain-encoding gene in amphibian limb regeneration. Gene 172 175. 

Rieker, J.P. Swanljung-Collins, H. Montibeller, J. Collins, J.H. Isolation and characterization of calmodulin-dependent myosin heavy chain kinase from intestinal brush border. Methods EnzymoL, 139, 105-114 (1987)... 

Most of the machinery of living cells is made of enzymes. Thousands of them have been extracted from cells and have been purified and crystallized. Many others are recognized only by their catalytic action and have not yet been isolated in pure form. Most enzymes are soluble globular proteins but an increasing number of RNA molecules are also being recognized as enzymes. Many structural proteins of the cell also act as catalysts. For example, the muscle proteins actin and myosin together catalyze the hydrolysis of ATP and link the hydrolysis to movement (Chapter 19). Catalysis is one of the most fundamental characteristics of life. 

The myofibrillar proteins make up 50-60% of the total protein of muscle cells. Insoluble at low ionic strengths, these proteins dissolve when the ionic strength exceeds -0.3 and can be extracted with salt solutions. Analysis of isolated mammalian myofibrils86 shows that nine proteins account for 96% or more of the protein myosin, which constitutes the bulk of the thick filaments, accounts for 43% and actin, the principal component of the thin filaments, 22%. 

That actin and myosin are jointly responsible for contraction was demonstrated long before the fine structure of the myofibril became known. In about 1929, ATP was recognized as the energy source for muscle contraction, but it was not until 10 years later that Engelhardt and Ljubimowa showed that isolated myosin preparations catalyzed the hydrolysis of ATP.138 Szent-Gyorgi139 140 showed that a combination of the two proteins actin (discovered by F. Straub141) and myosin was required for Mg2+-stimulated ATP hydrolysis (ATPase activity). He called this combination actomyosin. 

Studies of the myosin head, the globular part of the heavy chain together with the ELC and RLC, were dramatically transformed when the isolated myosin head from chicken skeletal muscle myosin was crystallized and its structure solved using protein crystallography by Rayment et al. (1993b Fig. 4A). This showed that the head consists of a globular... 

---