The effects of haem on translational control of protein synthesis in cell-free extracts from fed and lysine-derived Ehrlich ascites tumour cells

1. Addition of haem to cell-free extracts from Ehrlich ascites tumour cells stimulates protein synthesis only in extracts from cells previously incubated in nutritionally complete conditions. Extracts from amino-acid-deprived cells do not respond to haem. The stimulation of protein synthesis in fed cell extracts is due to increased initiation on endogenous mRNA mediated by an increase in the levels of 40-S-subunit X Met-tRNA initiation complexes. Extracts from starved cells exhibit a defect in 40-S initiation complex formation which cannot be overcome by haem. 2. Experiments to test for the presence of an inhibitor of initiation in Ehrlich cell extracts by monitoring effects on translation in haem-supplemented reticulocyte lysates have revealed that extracts from both fed and starved cells contain one or more inhibitory activities which shut off protein synthesis, dissagregate polysomes and reduce the level of 40-S initiation complexes in the lysate. Extracts from starved cells are more inhibitory for protein synthesis than those from fed cells. 3. Initiation factor eIF-2 is phosphorylated by an endogenous Ehrlich cell protein kinase in vitro, but this occurs to the same extent in extracts from fed and starved cells. 4. We propose a possible model for the role of eIF-2 in the control of protein synthesis by amino acid supply in Ehrlich cells.     

Simple methods for sampling periphyton with observations on sampler design criteria

Requirements for an ideal standard sampling system for defined periphyton communities are discussed. Several simple and inexpensive devices for both spatially discrete and continuous sampling modes are described and field tested in a variety of habitats.     

Searching for a model for use in vegetation analysis

Summary Indirect gradient analysis methods require an explicit vegetation model which must be based on direct gradient analysis studies. Various vegetation models are reviewed. Field evidence for the models is discussed. Experimental studies of species response to environmental gradients are reviewed and discussed. Three types of gradient are recognized as important for development of models: indirect environmental gradients where the environmental factor has no direct physiological influence on plant growth e.g. elevation; direct environmental gradients where the factor has a direct physiological effect on growth but is not an essential resource, e.g. pH; resource gradients where the factor is an essential resource for plant growth. The behaviour of the ecological carrying capacity and the role of competition along such gradients are shown to be important for developing vegetation models.     

The regeneration of coenzymes using immobilized hydrogenase

Summary A new enzymatic approach to the regeneration of coenzymes has been developed. It uses the reduction of natural or artificial cofactors with H₂, catalyzed by hydrogenase activity in immobilized whole cells ofA. eutrophus. The method has been employed for regeneration of such coenzymes as NAD⁺, FMN, phenazine methosulfate, Janus green, methylene blue, and 2,6-dichlorophenol-indophenol.     

An autoradiographic study of the flow of protein and RNA along peripheral nerve

Both chicken spinal cord and the posterior chamber of the rat eye have been injected with either [3H]leucine or [3H]orotic acid. The movement of newly synthesized protein and RNA down the sciatic and optic nerves was followed by means of autoradiography. Protein moved down both nerves by axoplasmic flow, the protein being confined to intra-axonal spaces. RNA appeared to move at about the same rate as protein, but much of the newly formed RNA appeared in structures outside the axons, particularly in Schwann and glial cells. There was, however a considerable proportion of the RNA inside the axons. This RNA may be involved in the direction of protein synthesis at sites along the axonal processes.     

The Ionic Permeability Changes during Acetylcholine-Induced Responses of Aplysia Ganglion Cells

ACh-induced depolarization (D response) in D cells markedly decreases as the external Na⁺ is reduced. However, when Na⁺ is completely replaced with Mg⁺⁺, the D response remains unchanged. When Na⁺ is replaced with Tris(hydroxymethyl)aminomethane, the D response completely disappears, except for a slight decrease in membrane resistance. ACh-induced hyperpolarization (H response) in H cells is markedly depressed as the external Cl^- is reduced. Frequently, the reversal of the H response; i.e., depolarization, is observed during perfusion with Cl^--free media. In cells which show both D and H responses superimposed, it was possible to separate these responses from each other by perfusing the cells with either Na⁺-free or Cl^--free Ringer's solution. High [K⁺]₀ often caused a marked hyperpolarization in either D or H cells. This is due to the primary effect of high [K⁺]₀ on the presynaptic inhibitory fibers. The removal of this inhibitory afferent interference by applying Nembutal readily disclosed the predicted K⁺ depolarization. In perfusates containing normal [Na⁺]₀, the effects of Ca⁺⁺ and Mg⁺⁺ on the activities of postsynaptic membrane were minimal, supporting the current theory that the effects of these ions on the synaptic transmission are mainly presynaptic. The possible mechanism of the hyperpolarization produced by simultaneous perfusion with both high [K⁺]₀ and ACh in certain H cells is explained quantitatively under the assumption that ACh induces exclusively an increase in Cl^- permeability of the H membrane.     

Mold Sensitivity in the Allergic Respiratory Diseases

A study to determine the role of mold allergens in the allergic respiratory diseases was made by reviewing the skin sensitivity reactions to molds of 257 consecutive cases of asthma and/or rhinitis in southwestern British Columbia. Failure to adequately seek out and to treat even minor mold allergy was noted to be a frequent cause of therapeutic failure or of only limited success. Apparently bearing a consistent relation to age and being most prevalent in the mature adult, allergy to fungi appeared to develop slowly and insidiously. The incidence of mold sensitivity was 78.5% and exceeded that of house dust sensitivity by 3.1%. Evidence of clinical sensitivity was present in excess of 52.4% of mold-sensitive patients. Asthmatic patients showed a greater incidence of sensitivity to molds and to multiplicity of species than did patients with rhinitis only. The hypothesized evolution of rhinitis to asthma appeared to be paralleled by the acquisition of sensitivity to increasing numbers of species of fungi. This suggests that the development of sensitivity to multiple mold species may be an etiologic factor in the production of the asthmatic state.