Myosin enzymatic activity

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. 

These high performance size exclusion separations of alpha-chymotrypsin SI and myosin light chains compare favorably with those achieved by ion exchange chromatography but require only a fraction of the time to accomplish. Furthermore, the very short retention times allow for separation of these labile proteins at room temperature, whereas operation at 0-40 C would otherwise be mandatory to avoid the loss of enzymatic activity. 

It is important to note that the binding of ATP places the /P, into the pocket formed by SW1 and the P-loop, which promotes the moving in of SW2. The effects of this movement are twofold the relay helix is kinked and thereby re-primed, and the enzymatically active site is formed. In the pre-powerstroke state, the nucleotide is completely enclosed by the positioning of SW1 and SW2. This conformation appears to be the enzymatically active form of myosin. Moreover, this is the preferred stable structure of myosin in the presence of nucleotide. 

Movement. Muscle contraction is accomplished by the interaction between two types of protein filaments, actin and myosin. Myosin also possesses an enzymatic activity for facilitating the conversion of the chemical energy of ATP into mechanical energy. 

Unfolding of globular proteins and subunits. Data on frozen storage of HMM, actin and sarcoplasmic enzymes have led us to propose that denaturation involves unfolding of the protein chain based on a decrease in enzymatic activity (myosin, HMM, and sarcoplasmic enzymes), polymerizing ability (actin) and filament forming properties (myosin) (82,99,113-116,122). 

Sata M, Stafford WF, 3rd, Mabuchi K, Ikebe M (1997) The motor domain and the regulatory domain of myosin solely dictate enzymatic activity and phosphorylation-dependent regulation, respectively. Proc Natl Acad Sci U S A 94 9196 Schoenberg M, Podolsky RJ (1972) Length-force relation of calcium activated muscle fibers. Science 176 5254... 

Siemankowski RF, Wiseman MO, White HD (1985) ADP dissociation from actomyosin subfragment 1 is sufficiently slow to limit the unloaded shortening velocity in vertebrate muscle. Proc Natl Acad Sci U S A 82 658662 Sivaramakrishnan M, Burke M (1982) The free heavy chain of vertebrate skeletal myosin subfragment 1 shows full enzymatic activity. J Biol Chem 257 11021105 Small JV (1977) Studies on isolated smooth muscle cells The contractOe apparatus. J Cell Sci 24 327349... 

Kelley CA, Sellers JR, Card DL, Bui D, Adelstein RS (1996) Xenopus nonmuscle myosin heavy chain isoforms have different subcellular localization and enzymatic activities. J Cell Biol 134 675-687... 

Sata M, Matsuura M, Ikebe M (1996) Characterization of the motor and enzymatic properties of smooth muscle long SI and short HMM role of the two-headed structure on the activity and regulation of the myosin motor. Biochem 35 1111311118... 

It has been established that SM-MyHC from vascular and visceral SM tissues differ by an insert of 7 amino acids at the 25-/50-kDa junction of the SI subfragment of the myosin head [50,51]. It is important to note that the two MyHC isoforms display distinct velocity of movement of actin filaments in vitro and actin-activated Mg +-ATPase activity. These data have been confirmed by Rovner et al. [67] who found that homogeneous populations of heavy meromyosin from tonic or phasic SM tissues incorporating or lacking the 7 amino acid insert near the active site of MyHC display different enzymatic and motility properties not influenced by the... 

When G-actin is mixed with an excess of L-myosin, the viscosity does not increase, but if ATP is then added, the increase is observed as soon as the ATP is broken down by the ATPase activity of the L-myosin. This means that G-actin is quantitathely bound by the L-myosin such that it cannot polymerize even in presence of salt. Polymerization takes place, however, when the G-actin is dissociated from the myosin on addition of ATP. As soon as the latter is enzymatically decomposed, L-myosin recombines with the actin, now present in the fibrous form, to give the highly viscous type of actomyosin (Straub, 1943). 

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... 

---