Correlation of enzymatic properties and conformation of bovine erythrocyte myosin

Myosin was purified from bovine erythrocytes by chromatography on DEAE-cellulose, Sepharose CL-4B, hydroxylapatite, and DEAE-5PW. The yield was about 200 micrograms/L of packed cells. From SDS-polyacrylamide gels, the purity was estimated to be greater than 95%. The bovine erythrocyte myosin is composed of heavy chains of 200 kDa and light chains of 20 and 17 kDa, in a molar stoichiometry of 1. Myosin was also purified from human erythrocytes by the same method. The molecular weights of two light chains were 26K and 19.5K which confirmed the earlier reports [Fowler, V. M., Davis, J. Q., & Bennet, V. (1985) J. Cell Biol. 100, 47-55; Wong, A. J., Kiehart, D. P., & Pollard, T.D. (1985) J. Biol. Chem. 260, 46-49]. Phosphorylation by gizzard myosin light chain kinase, to a level of 1 mol of phosphate/mol of 20-kDa light chain, increased actin-activated ATPase, and the extent of activation was dependent on the MgCl2 concentration. Both Ca2+-ATPase and Mg2+-ATPase activities were dependent on KCl concentration and markedly decreased below 0.3 M KCl. Mg2+-ATPase of phosphorylated myosin, while more resistant to decreasing ionic strength, was also decreased below 0.2 M KCl. These results are similar to those obtained with smooth muscle myosin and suggest that the 10S-6S transition occurs. In confirmation of this, gel filtration, viscosity, and electron microscopy (rotary shadowing) show that erythrocyte myosin forms extended and folded conformations in high and low salt, respectively. It is proposed that each conformation is characterized by distinct enzymatic properties.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vivid molecular divergence over volcanic remnants: the phylogeography of Megadromus guerinii on Banks Peninsula,New Zealand

Megadromus guerinii, an endemic carabid beetle (Carabidae), is the most common carabid throughout its restricted range on Banks Peninsula, a formation of extinct volcanoes in Canterbury, New Zealand. This study characterises the small-scale phylogeographic patterns of M. guerinii across the formerly volcanically active Banks Peninsula using mitochondrial and ribosomal genes. Between the eastern and western areas of the peninsula, the mitochondrial, but not nuclear, DNA has a well-defined geographic distribution. Specifically, mitochondrial cytochrome c oxidase subunit I (CO1) identifies two distinct groups (> 6% divergence between eastern and western beetles) while ribosomal genes show no discernible pattern. Whether such a pattern represents male-biased dispersal, Wolbachia infection, a recent range expansion of a divergent lineage, or a deeper historic separation is explored. There is potential that male-biased dispersal could have occurred. Wolbachia infection was not detected. We conclude that historical processes have likely separated taxa in the eastern and western peninsula.     

Association between chloroplast and mitochondrial lineages in oaks

Patterns of chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) variation were studied in 378 populations of oak trees sampled throughout the southern half of France. Six cpDNA haplotypes detected in a previous European survey and three new cpDNA haplotypes were found in this region. Two mitochondrial polymorphisms detected earlier by restriction analysis of PCR-amplified fragments alone, or in combination with single-strand conformation polymorphism (SSCP), were compared with the cpDNA data. Sequencing revealed the nature of the two mitochondrial mutations: a single-base substitution and a 4-bp inversion associated with a 22-bp hairpin secondary structure. The single-base substitution was then analyzed by allele-specific amplification. Results for the two cytoplasmic genomes were combined, which allowed the identification of 12 cpDNA-mtDNA haplotypes. The 4-bp mtDNA inversion has appeared independently in different cpDNA lineages. Given the peculiar nature of this mtDNA mutation, we suggest that intramolecular recombination leading to repeated inversions of the 4-bp sequence (rather than paternal leakage of one of the two genomes) is responsible for this pattern. Furthermore, the geographic locations of the unusual cpDNA-mtDNA associations (due to the inversion) usually do not match the zones of contact between divergent haplotypes. In addition, in southern France, the groupings of populations based on the mtDNA substitution were strictly congruent with those based on cpDNA. Because many populations that are polymorphic for both cpDNA and mtDNA have remained in contact since postglacial recolonization in this area without producing any new combination of cytoplasms involving the mitochondrial substitution, we conclude that paternal leakage is not a significant factor at this timescale. Such results confirm and expand our earlier conclusions based on controlled crosses.      

The reaction of myosin with N-ethylmaleimide in the presence of ADP

Myosin reacted with N-ethylmaleimide in the presence of ADP lost its ability to be activated by actin. Subfragment 1 behaved similarly. About 2 moles of N-ethylmaleimide per mole of Subfragment 1 were required to eliminate actin activation of the Mg²⁺-ATPase activity. At the point at which actin activation was lost the K⁺-EDTA-ATPase activity was also lost, but the Ca²⁺-activated ATPase activity was increased. Kinetic measurements indicated that the labelling with N-ethylmaleimide in the presence of ADP reduced V (the ATPase activity at infinite actin concentration) but did not effect K_app (which is related to the dissociation constant of the actin-Subfragment 1 complex). The Mg²⁺-activated activity of the reacted myosin alone remained unaltered and the ability to bind actin was retained. We propose that the N-ethylmaleimide labelling blocked the actin activation by preventing the accelerated release of hydrolysis products from the myosin.     

Effects of magnesium chloride on smooth muscle actomyosin adenosine-5'-triphosphatase activity, myosin conformation, and tension development in glycerinated smooth muscle fibers

The contractile system of smooth muscle exhibits distinctive responses to varying Mg2+ concentrations in that maximum adenosine-5'-triphosphatase (ATPase) activity of actomyosin requires relatively high concentrations of Mg2+ and also that tension in skinned smooth muscle fibers can be induced in the absence of Ca2+ by high Mg2+ concentrations. We have examined the effects of MgCl2 on actomyosin ATPase activity and on tension development in skinned gizzard fibers and suggest that the MgCl2-induced changes may be correlated to shifts in myosin conformation. At low concentrations of free Mg2+ (less than or equal to 1 mM) the actin-activated ATPase activity of phosphorylated turkey gizzard myosin is reduced and is increased as the Mg2+ concentration is raised. The increase in Mg2+ (over a range of 1-10 mM added MgCl2) induces the conversion of 10S phosphorylated myosin to the 6S form, and it was found that the proportion of myosin as 10S is inversely related to the level of actin-activated ATPase activity. Activation of the actin-activated ATPase activity also occurs with dephosphorylated myosin but at higher MgCl2 concentrations, between 10 and 40 mM added MgCl2. Viscosity and fluorescence measurements indicate that increasing Mg2+ levels over this concentration range favor the formation of the 6S conformation of dephosphorylated myosin, and it is proposed that the 10S to 6S transition is a prerequisite for the observed activation of ATPase activity. With glycerinated chicken gizzard fibers high MgCl2 concentrations (6-20 mM) promote tension in the absence of Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of phosphorylation on the actin-activated atpase activity of myosin

The purpose of this study was to test the hypothesis that the phosphorylation of myosin is solely responsible for the activation of the Mg²⁺-ATPase activity of gizzard actomyosin. Using a washed natural actomyosin and a reconstituted actomyosin it was shown that phosphorylation alone caused only a slight activation of ATPase activity. Full activity was obtained only when proteins in addition to the myosin light chain kinase were added. It is evident from these results that: 1) there is no simple relationship between the extent of myosin phosphorylation and the specific Mg²⁺-ATPase activity of actomyosin and 2) in order for full activation by actin of the Mg²⁺-ATPase activity of phosphorylated myosin additional factors are required.     

A novel protein phosphatase inhibitor, tautomycin. Effect on smooth muscle.

The antibiotic, tautomycin, was found to be a potent inhibitor of protein phosphatases and equally effective for the type-1 and type-2A enzymes. For the catalytic subunits of the type-1 and type-2A phosphatases the IC50 value was 22 to 32 nM. For the phosphatase activity present in chicken gizzard actomyosin the IC50 value was 6 nM. Tautomycin had no effect on myosin light chain kinase activity. Tautomycin induced a Ca(2+)-independent contraction of intact and permeabilized smooth muscle fibers and this was accompanied by an increase in the level of myosin phosphorylation. Thus, tautomycin by virtue of its ability to inhibit phosphatase activity is a valuable addition for studying the role of protein phosphorylation.     

Characterization of protein-protein interactions involved in iron reduction by Shewanella oneidensis MR-1

The interaction of proteins implicated in dissimilatory metal reduction by Shewanella oneidensis MR-1 (outer membrane [OM] proteins OmcA, MtrB, and MtrC; OM-associated protein MtrA; periplasmic protein CctA; and cytoplasmic membrane protein CymA) were characterized by protein purification, analytical ultracentrifugation, and cross-linking methods. Five of these proteins are heme proteins, OmcA (83 kDa), MtrC (75 kDa), MtrA (32 kDa), CctA (19 kDa), and CymA (21 kDa), and can be visualized after sodium dodecyl sulfate-polyacrylamide gel electrophoresis by heme staining. We show for the first time that MtrC, MtrA, and MtrB form a 198-kDa complex with a 1:1:1 stoichiometry. These proteins copurify through anion-exchange chromatography, and the purified complex has the ability to reduce multiple forms of Fe(III) and Mn(IV). Additionally, MtrA fractionates with the OM through sucrose density gradient ultracentrifugation, and MtrA comigrates with MtrB in native gels. Protein cross-linking of whole cells with 1% formaldehyde show new heme bands of 160, 151, 136, and 59 kDa. Using antibodies to detect each protein separately, heme proteins OmcA and MtrC were shown to cross-link, yielding the 160-kDa band. Consistent with copurification results, MtrB cross-links with MtrA, forming high-molecular-mass bands of approximately 151 and 136 kDa.     

Immunohistochemical localization of irisin in mole rats (Spalax leucodon)

Irisin was first identified in skeletal muscle cells. It is an exercise protein that is secreted into the circulation; it causes conversion of white adipose tissue to brown adipose tissue. We investigated irisin immunoreactivity in mole rat (Spalax leucodon) tissues. We examined cerebellum, pituitary, heart, liver, pancreas, spleen, uterus, kidney and striated muscle in female adult mole rats. Tissues were processed, embedded in paraffin, sectioned at 5 μm and stained immunohistochemically for irisin. Irisin immunostaining was detected in the cytoplasm of stained cells; the cytoplasm of Purkinje cells was unstained. We found that irisin may be synthesized in many tissues. The function of locally synthesized irisin currently is unknown.