Sequence similarities between chicken intestinal 110-kDa ATPase and myosin I-like enzymes

We report the partial amino acid sequence of chicken intestinal microvillar 110-kDa protein that, as a complex with calmodulin, has previously been shown to exhibit myosin-like ATPase and actin-binding activities. The sequence shows a high degree of similarity to the sequence of a novel vertebrate myosin I-like heavy chain encoded by a cDNA isolated from bovine intestine. This confirms that the bovine and chicken proteins are the first examples of Acanthamoeba myosin I-like proteins from higher eukaryotes. Comparison of available structural and functional data leads us to postulate that the myosin I family of proteins result from the fusion of a conserved myosin headlike motor domain, with variable COOH-terminal domains responsible for binding to specific intracellular structures.     

Interaction of (Na + K + 2 Cl) cotransport and the Na/K pump in cultured chick cardiac myocytes

We have recently reported the presence of an electroneutral (Na + K + 2 Cl) cotransport mechanism that is bumetanide-sensitive and maintains Cl_i above its electrochemical equilibrium in cultured chick heart cells. In steady state, (Na + K + 2 Cl) cotransport is inwardly directed and so contributes to the Na influx that must be counterbalanced by the activity of the Na/K pump to maintain Na_i homeostasis. We now show that manipulating (Na + K + 2 Cl) cotransport by restoring Cl_o to a Cl-free solution indirectly influences Na/K pump activity because the bumetanide-sensitive recovery of a _infNa ^supi to its control level and the accompanying hyperpolarization could be blocked by 10^–4M ouabain. In another protocol, when the Na/K pump was reactivated by restoring K_o (from 0.5 mM to 5.4 mM) and removing ouabain, the recovery of a_Na was attenuated by 10^–4M bumetanide. The relatively slow rate of ouabain dissociation coupled with the activation of Na influx by (Na + K + 2 Cl) cotransport clearly establishes the interaction of these transport mechanisms in regulating Na_i. Although (Na + K + 2 Cl) cotransport is electroneutral, secondary consequences of its activity can indirectly affect the electrophysiological properties of cardiac cells.     

The ras oncogene and tumour metastasis: observations on murine cells transfected with activated human c-Ha-ras

Transfection of cells with cloned genes or total genomic DNA offers a means for studying aspects of neoplastic behaviour. We have used this method to examine whether incorporation of the cloned 6.6-kilobase (kb) fragment of DNA containing the mutant c-Ha-ras human oncogene can confer metastatic capability on murine NIH 3T3 cells. Cells co-transfected with the mutated ras gene and the neomycin resistance marker pSV2neo were selected by culture in neomycin. On subcutaneous inoculation into MF 1 nude mice, these cells proved to be tumourigenic with short latent periods (approximately 14 days)--nude mice were used to circumvent immunological rejection of the mouse cells expressing the product of the human oncogene. Transfectants were capable of lung colonisation after intravenous injection, but there was no evidence of spontaneous metastasis at autopsy, or on histological examination of the lungs and other organs, 90 days after inoculation. Incorporation of the transfected oncogene was confirmed by Southern blotting and its expression by dot-blot hybridisation and immunoprecipitation. The results in this experimental system indicate that transfection of a mutated human ras oncogene into non-neoplastic 3T3 cells can confer part of the metastatic phenotype, namely lung colonisation, but is not by itself sufficient to induce spontaneous metastatic behaviour.     

Radiolysis of DNA in aqueous solution in the presence of a scavenger: A kinetic model based on a nonhomogeneous reaction of OH radicals with DNA molecules of spherical or cylindrical shape

Summary Two expressions are given for the survival dose of DNA exposed to high-energy radiation in aqueous solution in the presence of a scavenger. They are derived from a model where a diffusion controlled reaction of OH radicals occurs on the surface of the DNA macromolecules in competition with scavenging in the bulk of the solution. The DNA molecules are approximated either by spheres or by cylinders. The model based on molecules of spherical shape corresponds closely to that developed by van Rijn et al. [20]. Expressions obtained from the cylindrical model are used to account for the dependence on the scavenger concentration of some experimentally measured quantities, namely the survival dose and theG value for single-strand breaks upon Co -irradiation ofX 174 DNA and polyadenylic acid, respectively.In memoriam Prof. Dr. O.E. Polansky     

Structural comparison of the 68 kDa laminin-binding protein and 5'-nucleotidase from chicken muscular sources: evidence against a gross structural similarity of both proteins

The 68 kDa laminin-binding protein purified from chicken skeletal muscle and the ectoenzyme 5'-nucleotidase from chicken gizzard are both able to interact with laminin. They were both shown to possess a nearly identical amino acid composition. The 79 kDa glycosylated form of 5'-nucleotidase can be transformed into an enzymatically active form by treatment with endoglycosidase F (Endo F). Deglycosylated (Endo F-treated) 5'-nucleotidase exhibits an apparent molecular mass of 68 kDa. Using immunological and finger-printing techniques, both proteins were analysed to determine their structural relatedness. The results obtained indicate that both proteins are not identical but may posses a few common peptides of yet unknown sequence and length.     

Cell attachment properties of collagen type VI and arg-gly-asp dependent binding to its α2(VI) and α3(VI) chains

Twelve of sixteen different cell types including fibroblasts and tumor cells were able to attach and spread on substrates of pepsin-solubilized or intact collagen VI, and on its triple helical domain. Attachment and spreading were independent of soluble mediator proteins (fibronectin, laminin) and collagen VI was distinct from collagens I, IV and V in the cells with which it interacted. Many of the same cells bound and spread on substrates prepared from unfolded α2(VI) and α3(VI) chains but not on the α1(VI) chain. The interactions with the chains were inhibited by low concentrations (10–100 μM) of synthetic RGDS and RGDT but not RGES peptides while the binding of cells to pepsin-solubilized collagen VI was more than 20-fold less sensitive to these peptides. The data incidate that cells have the ability to bind to collagen VI in a specific manner suggesting a similar function for collagen VI in situ.     

Patterns of energy storage in Pseudoboeckella poppei (Crustacea,copepoda) from two contrasting lakes on Signy Island,Antarctica

The copepod Pseudoboeckella poppei (Daday) (Calanoida, Centropagidae) was sampled from Sombre and Heywood Lakes on Signy Island, Antarctica (60° S, 45° W) between January 1984 and March 1985. Sombre Lake is clear and oligotrophic with little phytoplankton and a bottom sediment low in organic content. By contrast Heywood Lake is turbid and mesotrophic; a substantial phytoplankton develops in summer and the bottom sediments are comparatively rich in organics. Both lakes freeze over for much of the year, forcing the copepods to adopt a benthic feeding strategy over winter. Adult Pseudoboeckella feed on phytoplankton when this is available, but also on detritus, diatoms and short algal filaments stirred up from the sediment. In Heywood Lake, male copepods show a smooth seasonal trend in lipid content with lipid being synthesised in early summer and utilised in late summer and winter. The summer increase in lipid content is associated with an increase in dry weight. Female lipid contents show evidence of two peaks of egg production. In Sombre Lake both male and female copepods increase in size during summer and show a wider range of lipid contents than in Heywood Lake; it is likely that this is due to the poorer winter feeding conditions which necessitate the synthesis of a much larger store of reserves during the summer. In contrast to marine calanoid copepods, lipid stores are exclusively triacylglycerol with no trace of wax ester.     

Regulation of nicotinic acetylcholine receptor function by adenine nucleotides

1. Nicotinic acetylcholine receptors (nAChR)4 from BC3H1 cells (which express a skeletal muscle-type receptor) and from Torpedo californica electric organ were expressed in Xenopus laevis oocytes and studied with a voltage-clamp technique. 2. We found that bath application of ATP in the micromolar to millimolar range increased the ACh-elicited current in both muscle and electrocyte receptors. The effect of ATP increased with successive applications. This "use-dependent" increase in potentiation was Ca2+ dependent, while the potentiation itself was not. 3. Four other nucleotides were tested on muscle nAChR: ADP, AMP, adenosine, and GTP. Of these, only ADP was a potentiator, but its effect was not use dependent. Neither ATP nor ADP affected the resting potential of the oocyte membrane. 4. ADP potentiated the response to suberyldicholine and nicotine, as well as ACh. 5. Finally, ADP reversed the phencyclidine-induced block of ACh currents in oocytes expressing muscle nAChR.     

Affinity labeling of spinach phosphoribulokinase subsequent toS-methylation at Cys16

The chloroplast enzyme phosphoribulokinase is reversibly deactivated by oxidation of Cys16 and Cys55 to a disulfide. Although not required for catalysis, Cys16 is an active-site residue positioned at the nucleotide-binding domain (Porter and Hartman, 1988). The hyperreactivity of Cys16 has heretofore limited further active-site characterization by chemical modification. To overcome this limitation, the partially active enzyme,S-methylated at Cys16, has been probed with a potential affinity reagent. Treatment of methylated enzyme with bromoacetylethanolamine phosphate results in essentially complete loss of catalytic activity. Inactivation follows pseudo-first-order kinetics and exhibits a rate saturation with an apparentK _d of 3–4 mM. ATP, but not ribulose 5-phosphate, affords substantial protection. Complete inactivation correlates with incorporation of 1 mol of [¹⁴C]reagent per mole of enzyme subunit. Amino acid analysis of the [¹⁴C]-labeled enzyme demonstrates that only cysteine is modified, and mapping of tryptic digests shows that Cys55 is a major site of alkylation. These results indicate that Cys55 is also located in the ATP-binding domain of the active-site.