Location of a delta-subunit region determining ion transport through the acetylcholine receptor channel

The combination of complementary DNA expression and single-channel current analysis provides a powerful tool for studying the structure-function relationship of the nicotinic acetylcholine receptor (AChR) (refs 1-5). We have previously shown that AChR channels consisting of subunits from different species, expressed in the surface membrane of Xenopus oocytes, can be used to relate functional properties to individual subunits. Here we report that, in extracellular solution of low divalent cation concentration, the bovine AChR channel has a smaller conductance than the Torpedo AChR channel. Replacement of the delta-subunit of the Torpedo AChR by the bovine delta-subunit makes the channel conductance similar to that of the bovine AChR channel. To locate the region in the delta-subunit responsible for this difference, we have constructed chimaeric delta-subunit cDNAs with different combinations of the Torpedo and bovine counterparts. The conductances of AChR channels containing chimaeric delta-subunits suggest that a region comprising the putative transmembrane segment M2 and the adjacent bend portion between segments M2 and M3 is involved in determining the rate of ion transport through the open channel.     

Laser diffraction used to monitor strain in mechanoreceptors ofJasus verreauxi

Summary Laser diffraction patterns from crayfish abdominal mechanoreceptors have been observed and the corresponding sarcomere lengths calculated and then correlated with sensory nerve discharge frequencies.Our thanks are due to the Australian Research Grants Committee for provision of the lasers and camera, to Dr.K. S. Imrie for the design of the interfacing cards, to ProfessorP. Mason and ProfessorR. E. Aitchison for their encouragement and advice, and toI. Paterson andC. March for constructing the equipement.     

The effect of two new peptide antibiotics,the hypelcins,on mitochondrial function

Summary The action on mitochondria of 3 peptide antibiotics, hypelcin-A, hypelcin-B, and alamethicin, was examined. The results showed that they are unique uncouplers of oxidative phosphorylation, with the same mechanism of action.     

Inhibitory effect of cytokinins on PHA-induced human lymphocyte stimulation

Summary The inhibitory effect of various purine derivatives on PHA-induced human lymphocyte blast formation was studied. Two nucleoside cytokinins, N⁶-benzyladenosine and N⁶-isopentenyladenosine, inhibited blast formation at concentrations as low as 10^–6 M. However, the other cytokinins, which lacked the ribosyl residue at N⁹ position, had to be at the higher molar concentration of 10^–4 before they could induce the same inhibitory effect.     

Permeability of fresh and stored human erythrocytes to glycerol and its acylated derivatives

Summary The effect of copper ions on the permeation of glycerol and its mono-, di-, and triacetate derivatives was studied in fresh and stored erythrocytes. Permeability was unchanged with storage. Acylated glycerols permeate the cells mainly by non-facilitated mechanism, as their transport is almost unaffected by copper ions.Portions of this work were included in the graduate thesis of Dr. Yaeger in partial fulfillment of the requirements for the M. D. degree.Acknowledgement. We thank Mrs Dalia Mazor for expert technical assistance.     

Furospongolide,a new C21 furanoterpene from a marine organism

Summary The structure of a new linear C₂₁ furanoterpene, furospongolide (1), obtained from the marine spongeDysidea herbacea, was determined by spectral means.We thank Professor J. Vacelet for the identification and Dr Loya and Mr Benayahu for the collection of the sponge.     

Isolation and partial characterization of receptor sites of normal human lymphocytes for lectins]

Glycoproteins of the lymphocyte surface are involved in many membrane mediated events. Their specific carbohydrate determinants might interact with lectins. Purification of macromolecules released from normal human lymphocytes by trypsin was performed using gel filtration and affinity properties for Ricinus sanguineus agglutinin. Some structural and biochemical characteristics are given. Relation to HLA determinants and surface immunoglobulins is discussed.     

Loss of cytosolic serine hydroxymethyltransferase in a formate mutant ofNeurospora crassa

Summary In the wild type ofNeurospora crassa serine hydroxymethyltransferase occurs in the cytosol and mitochondria. The formate mutant (FGSC 9) lacks the cytosolic activity but has increased levels of isocitrate lyase and glyoxylate aminotransferase. Glycine is derived from glyoxylate in the mutant.     

Lipoperoxide formation in the retina in ocular siderosis

Summary Insertion of iron nail into the vitreous cavity provoked the formation of lipoperoxide in the retina. In accord with the increase in lipoperoxide in the retina, ERG began to decrease. In vitro experiment using isolated retina, lipoperoxide was found to be increased in the presence of ferric or ferrous ions, while it was inhibited by adding antioxidants or ethylenediamine tetraacetate. From these results, direct cause of retinal degeneration in siderosis could be ascribed to the formation of lipoperoxide by iron-ions liberated from the piece of iron, resulting into the degeneration of the visual cell layers of the retina.