Myosin, enzymatic hydrolysis

Enzymatic activities. The hydrolysis of ATP by actin-activated myosin is the characteristic enzymatic activity of muscle, smooth muscle included. All forms of smooth muscle myosin are slower than those of other muscles. The binding site for ATP and a reduced enzymatic activity are still present in monomeric myosin. The enzymatic activity of monomeric myosin is altered by a conformational change, (the 10S-6S transition) and the species of cations present in the reaction mixture. These differences relate to the possible mechanisms of regulation. 

Phosphate in combination with NaCl has a beneficial effect on the waterbinding capacity of processed meat products for a detailed description, see Schmidt.227 The effect of phosphates is suggested to be alterations in pH or ionic strength, sequestration of metal ions, dissociation of actomyosin and depolymerisation of myosin.103,104,228,229 However, before action, added phosphates must be hydrolysed by muscle phosphatases or non-enzymatically. Belton et al.230 studied the hydrolysis of pyrophosphate and tripolyphosphate in comminuted chicken meat using 31P NMR spectroscopy, and found that the rate of hydrolysis was dependent on the length of ageing period of the muscle as well as the presence of NaCl. Li et al.231 studied the hydrolysis of various types of phosphates in intact chicken muscle with a similar approach by 31P NMR spectroscopy and thereby demonstrated differences in rate of hydrolysis of various phosphates. The findings of these studies... 

Without any doubt, one of the most extensively sttidied enzyme reaction by transient kinetics is the ATPase activity of the subfragment-1 (SI) of myosin. This proteolytic product constitutes the heads of the myosin molecule, which has, in addition, a hinge and a tail component (see figure 4.11). SI contains the fully competent enzymatic site and also the site for attachment to actin, the thin filament of the myofibril. The interaction between SI and actin, discussed in section 6.4, is the key process in muscle contraction, and is controlled by the steps in ATP hydrolysis (Geeves et al., 1984 Geeves, 1991). The reciprocal relation between the modtilation of the... 

The phenomena of cytoplasm streaming and muscle contraction are generally related to enzymatic catalysis of ATP hydrolysis by the actin-myosin (A-M) system [1]. Therefore, by assuming a common driving mechanism, a simple question is raised What comes first -streaming or contraction ... 

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