L-Meromyosin

Similar studies were performed on the subunits L-meromyosin and H-meromyosin. In the former 90 % of the phenolic groups appear abnormal, but they are titrated normally in 5 M urea. In H-meromyosin all of the groups are normal, even in aqueous solution. 

It is of interest that the Si subfragment, the head of the myosin molecule, does not induce any aggregation in the presence of connectin (Maruyama et al., 1985a). However, heavy meromyosin interacted with connectin to form aggregates. The neck portion S2 of myosin did not act on connectin. L-Meromyosin and the rod portion of myosin were markedly... 

Calcium ion has a very specific effect on trypsin (Gorini, 1951), and Mn++ and Cd++ act similarly. However, other bivalent ions such as Mg++, Ba++, Si, Co++, Cu", or Ni++ are without effect (Nord and Bier, 1953). Duke, Bier, and Nord (1952) found that calcium increased the acidity of the carboxyl groups of trypsin between pH 3.5 and 5, and concluded that this was due to chelation of Ca++ with carboxyl groups. Their titration curves for trypsin in the presence of CaCh, MgCh, and KCl are shown in Fig. 5. At pH below 3 the enhanced acidity due to Ca++ disappears, since chelation with undissociated carboxyl groups is impossible. Nanninga (1954) has made a similar observation in the titration of L-meromyosin in the presence of Mg++. 

Subunits of Myosin. Matsumoto et al. (64) isolated H-meromyosin (HMM) and L-meromyosin (LMM) from carp muscle (15) and studied their stabilities at — 20°C. The ATPase activity of HMM decreased much faster than that of myosin and the capacity of HMM to bind with F-actin as determined by electron microscopy was lost. LMM also exhibited a decreased capacity to form well-ordered paracrystals. These results tend to indicate that frozen storage causes myosin molecules to aggregate side-by-side and myosin subunits to undergo conformational deformations. 

Lowey, S., Goldstein, L., Cohen, C., Luck, S.M. (1966). Proteolytic degradation of myosin and the meromyosins by a water-insoluble polyanionic derivative of trypsin. J. Mol. Biol. 23,287-304. 

When myosin is digested with trypsin, two myosin fragments (meromyosins) are generated. L ht mero-myosin (LMM) consists of aggregated, insoluble a-he-hcal fibers from the tail of myosin (Figure 49 ). LMM... 

Myosin. Rabbit muscle myosin is a long, thin molecule (VI400 X 20-50 A) with a molecular weight of 5 X 10. It is composed of two heavy chains and four light chains as demonstrated by SDS-polyacrylamide disc gel electrophoresis. On tryptic digestion, myosin is split into the subunits, H-meromyosin (HMM) and L-mero-myosin (LMM). HMM is further split into S-l and S-2 subunits. While LMM is a rod of V)0% a-helical content, the a-helical content for HMM, S-l and S-2 fragments is 46%, 33% and 87%, respectively. The ATPase activity is localized in the S-l subunit (33,34). Although fish myosins appear to have the same structural profile (10,22,35-40) and similar amino acid composition as rabbit myosin (39,41,42), fish myosin is different from rabbit myosin in physicochemical properties such as solubility, viscosity and stability (10,22,35-40). 

Other Polyphosphates.—The hydrolysis of the fluorescent l,A -ethenoadeno sine triphosphate (28) by myosin, and the fluorescence change observed on binding to heavy meromyosin, have been investigated, along with equili-... 

Hydroxyethyl)-piperazine-l-ethane-sulfonic acid Heavy meromyosin... 

Velaz L, Ingraham RH, Chalovich JM (1990) Dissociation of the effect of caldesmon on the ATPase activity and on the binding of smooth heavy meromyosin to actin by partial digestion of caldesmon. J Biol Chem 265 2929-2934... 

Kouyama, T. and Mihashi, K. (1981) Fluor-imetry study of N-(l-pyrenyl) iodoacetamide-labelled E-actin. Local structural change of actin protomer both on polymerization and on binding of heavy meromyosin. Eur. J. Bio-ehem. 114, 33-38. 

Figure 4.11 (a) Diagrammatic representation of the myosin filament and its interaction with the actin filament during the ATP hydrolysis cycle. More detail of the steps involved is given in section S.l. (b) Outline of the composition of the myosin molecule indicating the SI head of each chain, which contains both the active site for the ATPase reaction and the actin binding site. The proteolytic cleavage sites, a and b, are involved in the production SI and the double headed heavy meromyosin (HMM) respectively. 

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