Iodine distribution in the thyroid follicles of the hagfish,Eptatretus burgeri and lamprey,Lampetra japonica: Electron-probe X-ray microanalysis

Summary In the thyroid follicles of species of cyclostomes, a hagfish and a lamprey, the distribution of stable iodine was examined by electron-probe X-ray microanalysis. A high concentration of stable iodine, heterogeneously distributed, was observed in the follicular cells of hagfish thyroid follicles. In the lamprey a low concentration of iodine was seen in the follicular lumina. The relative values for stable iodine determined in this way corresponded to values obtained by a chemical analytical method.     

Modification of the gene 5 DNA unwinding protein with ruthenium

A chemical modification of the gene 5 DNA binding protein (G5BP) from bacteriophage fd was investigated using X-ray diffraction and difference Fourier analysis. The crystalline protein was reacted with pentaammineruthenium (III) trichloride, Ru(NH₃)₅Cl₃, a reagent believed specific for histidine residues and useful in NMR and chemical modification studies of proteins. The major ruthenium site was found by difference Fourier analysis to be 4 Å from histidine 64, the only histidine residue in the molecule. A second bipartite site, believed to be a ruthenium-anion pair, appeared to be salt-bridged to glutamic acid 40 and arginine 16. Indications were present in the difference Fourier results to suggest that the loop containing tyrosine 41 had undergone a slight conformational rearrangement to accommodate this interaction.     

Germacranolides from Schkuhria anthemoidea

The isolation of eucannabinolide and three new sesquiterpene lactones from Schkuhria anthemoidea is reported. The structures and stereochemistries of the new compounds were established by chemical and spectroscopic means. The structure of santhemoidin B was confirmed by X-ray crystallography.     

Resistance to Disruption of Multilamellar Fragments of Central Nervous System Myelin

Abstract: Single-bilayer vesicles of myelin are desirable for studying myelin development and metabolism. Accordingly, our interest was drawn to a procedure for ves-iculating myelin (Steck et al., Biochim. Biophys. Acta 509, 397–408, 1978). We used X-ray diffraction analysis to examine these putative vesicle preparations because much larger amounts of material can be surveyed by this method than by electron microscopy. The sharpness (width) of the rings in the X-ray diffraction pattern varies inversely with the number of bilayers per multilayer structure. We therefore expected to see the diffuse diffraction pattern characteristic of single bilayers. Diffraction patterns were recorded from isolated rat brain myelin before and after the vesiculation procedure. Both patterns showed sharp rings, indicating numerous multilayered structures. Average values ranging from 7 to 10 bilayers per multilayer were calculated in both cases. This procedure did produce a small fraction of single-bilayer structures, which were isolated by differential centnfu gation; however, these accounted for only about 1% of the total myelin present. The diffraction pattern of this material showed the diffuse band typical of single-bilayer structures, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated it had the same protein composition as in normal myelin. Similar results were also obtained using either fresh or frozen bovine brain myelin. Variations of the published vesiculation procedure (incubation in 0.1 M NaCl or in buffers containing glycerol; disruption by sonication or use of a Tissumizer) also were not effective in breaking down the multilamellar fragments into thinner structures. We conclude that the multilamellar fragments of isolated CNS myelin resist disruption into single-bilayer structures.     

Accumulation and subcellular distribution of cations in relation to the growth of potassium-deficient barley

Abstract Growth of barley (Hordeum vulgare L., cv. Georgie) was insensitive to soil K content above about 150 mg kg^?1, but at lower levels it declined. The reduction in yield was greater in soils containing approximately 10 mg Na kg^?1 than in soils with about 90 mg kg^?1 of Na. Growth was unaffected by changes in shoot K concentration above 75 mol m^?3, but declined at lower concentrations, and the decrease was less in plants grown in soils with high Na. Growth responses were not simply related to tissue K concentrations because plants grown in soils with extra Na had higher yields but lower K concentrations. When soil Na was low, plants accumulated Ca as tissue K declined, but when Na was provided this ion was accumulated. Plant Mg concentrations were generally low but increased as K decreased. The Ca and Mg were osmotically active. There were highly significant inverse linear relationships between yield and either the Ca or Mg concentrations in the shoots. X-ray microanalysis was used to examine the compartmentation of cations in leaves from barley plants (cv. Clipper) grown in nutrient solutions with high and low K concentrations. In plants grown with 2.5 mol m^?3 K, this was the major cation in both the cytoplasm and vacuole of mesophyll cells. However, in plants grown with 0.02 mol m^?3 K it declined to undetectable levels in the vacuole, although it was still detectable in the cytoplasm. In all plants, Ca was mainly located in epidermal cells. The implication of the results for explaining responses to K. in terms of compartmentation of solutes is discussed.     

Backbone side-chain interactions in peptides

IR, ¹H-NMR and X-ray experiments have been carried out on dipeptides with the Pro-Asp and Pro-Asn sequences protected on both ends by amide groups. The Pro-Asp dipeptide was investigated for the carboxylic, methyl ester and carboxylate forms of the Asp residue.In solution, all dipeptides are found to accommodate almost exclusively the I-turn conformation stabilized by an interaction between the Asp or Asn-NH and CO bonds. The I-turn percentage roughly parallels the basicity of the Asp or Asn side substituent, and decreases from Asp^- to Asn, and to Asp or Asp (OMe).The I-turn, stabilized by the interaction involving the Asp-CO site, is retained in the crystal structure of the Pro-Asp(OMe) dipeptide. The Pro-Asp and Pro-Asn dipeptides assume a II-turn conformation in the solid state and the polar Asp or Asn side-groups are involved in a complex network of intermolecular interactions.     

Polymorphic phase behaviour of dilinoleoylphosphatidylethanolamine and palmitoyloleoylphosphatidylcholine mixtures: Structural changes between hexagonal,cubic and bilayer phases

The polymorphic phase behaviour of dilinoleoylphosphatidyethanolamine (DLPE) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) is investigated by freeze-fracture electron microscopy, X-ray diffraction and ³¹P-NMR. The structures at 5% or less POPC are predominantly inverted hexagonal (H_II), whereas at 15% or more POPC, the structure is mostly bilayer (L), interrupted by defects (lipidic particles). A cubic phase structure is observed in the transition range between H and L phases; the cubic arrangement deteriorates at higher temperatures into an amorphous aggregate of spherical units. Both cubic and amorphous structures contribute to the isotropic ³¹P resonance, with no preference for PC or PE partitioning in the isotropic motion as observed by high resolution NMR. The existence of the cubic phase seems to depend critially on the homogeneity and the degree unsaturation of the phospholipids.     

Proteins of the Bacillus stearothermophilus ribosome: Crystallization of protein L6

Crystals of ribosomal protein L6 from Bacillus stearothermophilus suitable for high resolution structural studies have been obtained. Crystals are hexagonal with space group P6₁22 (or the enantiomorph P6₅22) and cell dimensions a = b = 72.7 Å, c = 124.9 Å. A search for heavy atom derivatives is in progress.     

The determination of the separate Ca pump protein and phospholipid profile structures within reconstituted sarcoplasmic reticulum membranes via X-ray and neutron diffraction

We have previously compared the electron density profiles for several highly-functional reconstituted sarcoplasmic reticulum membranes with that for the isolated sarcoplasmic reticulum membrane (Herbette, L., Scarpa, A., Blasie, J.K., Wang, C.T., Saito, A. and Fleischer, S. (1981) Biophys. J. 36, 47–72). In this paper, we compare the separate calcium pump protein profile within these reconstituted sarcoplasmic reticulum membranes, as derived by X-ray and neutron diffraction methods, with that within isolated sarcoplasmic reticulum membranes. In addition, the time-average perturbation of the lipid bilayer by the incorporated calcium pump protein within these reconstituted sarcoplasmic reticulum membranes has been determined in some detail.