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Fifty years ago, an important paper appeared in Botanical Magazine Tokyo. Kamiya and Kuroda proposed a sliding theory for the mechanism of cytoplasmic streaming. This pioneering study laid the basis for elucidation of the molecular mechanism of cytoplasmic streaming--the motive force is generated by the sliding of myosin XI associated with organelles along actin filaments, using the hydrolysis energy of ATP. The role of the actin-myosin system in various plant cell functions is becoming evident. The present article reviews progress in studies on cytoplasmic streaming over the past 50 years.

To investigate a possible heterogeneity of human ventricular myosin, papillary muscles of patients with valvular dysfunction were examined using a modified native gel electrophoresis. Myosin was separated into 2 components termed V A and V B , whereby the V A to V B proportion appeared to depend on the ventricular load. The proportion of the faster migrating band V A was correlated (P < 0.05) with end-diastolic pressure and the aortic pressure-cardiac index product. The regression based on these variables accounted for 67% of the variation in V A (R 2 = 0.67). The V A proportion was, however, not significantly correlated with cardiac norepinephrine concentration. The ATPase activity of the 2 components of myosin was assessed from the Ca 3 (PO 4 ) 2 precipitation by incubating the gel in the presence of ATP and CaCl 2 . The ATPase activity of V A was 60% of that of V B . The V A and V B forms were observed also in the cat (31.4% V A ), dog (32.1% V A ), pig (28.5% V A ), wild pig (33.7% V A ), and roe deer (30.5% V A ). V A and V B were not detected in the rat exhibiting the 3 isoforms V 1 , V 2 , and V 3 , rabbit (100% V 3 ), and hare (86% V 1 ). The data demonstrate a heterogeneity of large mammalian ventricular myosin, whereby an increased cardiac load appeared to be associated with a higher myosin V A proportion that exhibited a reduced ATPase activity.

:  Enzymatic and structural properties of white croaker fast skeletal muscle myosin were determined and compared with those of walleye pollack counterpart. Ca2+‐ATPase activity of white croaker myosin was decreased to approximately 70% of the original activity during 1 day of storage at 0°C and pH 7.0 in 0.5 M KCl and 0.1 mM dithiothreitol, whereas that of walleye pollack was decreased to approximately 20% under the same condition. The activation energy (Ea) for inactivation of white croaker myosin calculated by the Arrhenius plot for inactivation rate constant (KD) was 1.2‐fold higher than that of walleye pollack. While Ca2+‐ATPase showed a similar KCl‐dependency for the two species, the maximal activity was observed at pH 6.2 and 6.3 for white croaker and walleye pollack, respectively. Actin‐activated myosin Mg2+‐ATPase activity of white croaker was approximately half that of walleye pollack at 0.05 M KCl and pH 7.0, although the two myosins showed a similar affinity to F‐actin with Km of 1.7 and 1.4, respectively. Limited proteolysis with α‐chymotrypsin cleaved heat‐denatured white croaker myosin mainly at heavy meromyosin/light meromyosin (HMM/LMM) junction, whereas walleye pollack myosin was cleaved at several sites in LMM as well as at the HMM/LMM junction.

Lactoferrin is an iron-binding glycoprotein that belongs to the transferrin family. Recent studies in vitro and in vivo suggest that lactoferrin is a potential therapeutic agent for wound healing. We have shown that both bovine and human lactoferrin enhance the collagen gel contractile activity of WI-38 human fibroblasts. The collagen gel contraction is considered as an in vitro model for reorganization of the collagen matrix during the wound healing process. The elevation of collagen gel contractile activity induced by lactoferrin was accompanied by activation of extracellular-regulated kinase (ERK) 1/2 and myosin light chain kinase (MLCK), and subsequent elevation of myosin light chain (MLC) phosphorylation. The effects of lactoferrin on collagen gel contraction and the activation of the signaling pathway were dependent on the expression of low-density lipoprotein receptor - related protein (LRP) - 1 in the fibroblasts. LRP-1 is known as an endocytosis receptor and is involved in the cellular uptake of diverse ligands, including lactoferrin. In addition, LRP-1 acts as a signaling lactoferrin receptor in mammalian cells by converting the lactoferrin-binding signal into the activation of the intracellular signaling pathway. This property was found to be independent of the endocytic function of LRP-1, as seen in osteoblast-like cells.

We investigated the activity of P 21 -activated kinase-1 (Pak1) on myosin light chain phosphorylation and on thrombin-induced barrier dysfunction in human endothelial cells (HMEC). HMEC were infected with recombinant adenoviruses that express constitutively active Pak1, LacZ, wild-type, and a mutant myosin regulatory light chain, mMLC 20 (Thr18Ala, Ser19Ala). Expression of the recombinant Pak1 mediated by adenovirus in HMEC was regulated. Active Pak1 induced dephosphorylation of MLC 20 in HMEC, but not in smooth muscle cells. Active Pak1 significantly inhibited thrombin-induced endothelial barrier dysfunction. Expression of the unphosphorylatable MLC 20 also inhibited thrombin-induced endothelial barrier dysfunction. Constitutively active Pak1 associated with phosphatase 2A and induced a post-translational modification of the phosphatase. Our data provide novel evidence indicating that Pak1 regulates endothelial barrier function through activation of phosphatase 2A.

The effects of specific marinades on the thermal stability of the muscle proteins using differential scanning calorimetry (DSC) was examined. Various marinades were tested, composed mainly of NaCl as well as triphosphates and organic acids, self made marinades, and ready-to-use marinades used in industrial practice. As a result of the experiment conducted, it was found that all marinades used changed significantly the thermal stability of muscle proteins. The use of sodium chloride and sodium triphosphate for marination caused a reduction of enthalpy and denaturation temperature of myosin and actin. However, a greater influence on the stability of muscle proteins was observed with marinades containing organic acids (acetic and citric). The most significant reduction of the denaturation temperatures and enthalpy (to the lowest level of 0.56 J/g) was found for self made marinade composed of 20.7% cider vinegar and 16% lemon juice.

:  Thermally induced gelation of paramyosin from scallop smooth adductor muscle was investigated by dynamic rheological measurements under various conditions. The paramyosin thermal gel was produced at pH 6.5 and 7.2 at temperatures above 30°C through a two‐step increase in storage (G′) and loss (G′′) moduli; these values were higher than in gels produced from actomyosin at a high temperature. The thermal gel properties were very firm and brittle. In contrast, one main peak of G′ was observed during gelation at pH 8.0. The gel produced at pH 8.0 was more transparent and less soluble in a 6 M urea−0.5 M NaCl solution than those formed either at pH 6.5 or 7.2. These differences in the thermal gel properties are presumed to derive from the pH dependence of the gel matrix‐forming process, such as oxidative cross‐linking between cysteine residues, rather than from the thermal unfolding of the paramyosin molecules. The thermal gelation profile of chymotrypsin‐digested paramyosin showed marked depression of G′ at high temperature.

Transcellular transport affects the paracellular flux through 2 distinct mechanisms: by determining the driving force and by altering the permeability of the paracellular pathway. Such coordination ensures efficient transepithelial transport by preventing the build-up of large electrical and osmotic gradients. The regulation of paracellular permeability was originally recognized as increased paracellular flux of water and solutes upon the activation of the intestinal Na + -coupled glucose uptake. Despite great advances in the molecular characterization of the tight junctions that form the structural basis of epithelial barrier functions, the mechanisms whereby apical transporters alter the paracellular pathways remains unresolved. Recent studies suggest that myosin-based contractility is central to this coupling. In this minireview, we summarize our current knowledge of paracellular permeability, its regulation by contractility, and the various signaling events that link apical Na + -glucose cotransport to myosin phosphorylation. While the role of myosin phosphorylation appears to be universal, the mechanism(s) whereby apical transport triggers this process is likely cell specific. The current model suggests that in intestinal cells, a key factor is a p38 MAP kinase-induced Na + /H + -exchanger-mediated alkalinization. We propose an alternative, nonexclusive mechanism in kidney tubular cells, in which the key event may be a Na + -cotransport-triggered plasma membrane depolarization, which in turn leads to Rho-mediated myosin phosphorylation.

Thyroid hormone-induced cardiac hypertrophy is similar to that observed in physiological hypertrophy, which is associated with high cardiac contractility and increased α-myosin heavy chain ( α-MHC, the high ATPase activity isoform) expression. In contrast, angiotensin II (Ang II) induces an increase in myocardial mass with a compromised contractility accompanied by a shift from α-MHC to the fetal isoform β-MHC (the low ATPase activity isoform), which is considered as a pathological hypertrophy and inevitably leads to the development of heart failure. The present study is designed to assess the effect of thyroid hormone on angiotensin II-induced hypertrophic growth of cardiomyocytes in vitro. Cardiomyocytes were prepared from hearts of neonatal Wistar rats. The effects of Ang II and 3,3′,5-triiodo-thyronine (T 3 ) on incorporations of [ 3 H]-thymine and [ 3 H]-leucine, MHC isoform mRNA expression, PKC activity, and PKC isoform protein expression were studied. Ang II enhanced [ 3 H]-leucine incorporation, β-MHC mRNA expression, PKC activity, and PKC ε expression and inhibited α-MHC mRNA expression in cardiomyocytes. T 3 treatment prevented Ang II-induced increases in PKC activity, PKC ε, and β-MHC mRNA overexpression and favored α-MHC mRNA expression. Thyroid hormone appears to be able to reprogram gene expression in Ang II-induced cardiac hypertrophy, and a PKC signal pathway may be involved in such remodeling process.

The cryoprotective effects of trehalose and maltose (w = 2-10%) on washed beef meat were investigated. Washed beef meat produced from fresh beef meat was frozen and stored for 360 days at -30 deg C. Myofibrillar protein functional stability was monitored by salt extractable protein and differential scanning calorimetry. Salt extractable protein showed that the addition of trehalose and maltose caused a small loss of protein solubility during the frozen storage. Peak thermal transition and denaturation enthalpy of myofibrillar proteins were evaluated. Differential scanning calorimetry revealed a shift in the peak thermal transition temperature of myosin and actin to higher temperature as the mass fractions of trehalose and maltose increased. The transitions enthalpies of myosin and actin of the washed beef meat samples showed a higher increase with the increase of mass fraction of trehalose than of that of maltose. Since the value of denaturation enthalpy is directly related to the amount of native proteins, higher values of denaturation enthalpy point to higher cryoprotective effects of trehalose.