Lennart C. Eriksson

Structural investigation and hydrogen capacity of CaMg2Ni9: a new phase in the AB2C9 system isostructural with LaMg2Ni9

Abstract A new ternary magnesium-based alloy CaMg 2 Ni 9 has been synthesized, and its crystal structure was determined by Guinier–Hagg X-ray and neutron powder diffraction. The compound has a hexagonal structure and is isostructural with LaMg 2 Ni 9 type, with Ca at the La atom site. The hydrogen absorption/desorption properties have been determined by thermal analysis and pressure–composition isotherms. The electrochemical properties of the alloy were also examined.

Crystal structure determination and rietveld refinement of Zn(OH)(NO3) · H2O

Abstract The crystal structure of Zn(OH)(NO3) · H2O has been studied by X-ray diffraction methods using fibrous microcrystals and powder. The cell dimensions are a = 17.951 A, b = 3.2600 A, c = 14.272 A, and β = 114.91°. The space group is P2 1 c . The structure has been refined by the Rietveld full-profile technique. The results obtained from different data sets and the corresponding discrepancy indicators are compared. The structural chemistry of the compound is discussed and an interpretation of its topotactic transformation into Zn3(OH)4(NO3)2 is presented.

Preparation of liver microsomes with high recovery of endoplasmic reticulum and a low grade of contamination

A modified procedure for preparing the microsomal fraction from rat liver was developed with the aim of increasing the recovery without increasing the degree of contamination. 87% of the membranes of the microsomal fraction isolated from the first mitochondrial (10 000 X g) supernatant originates from the endoplasmic reticulum, representing a 35% yield. By gentle resuspension of the 10 000 X g pellet followed by differential centrifugation a second crop of microsomes can be prepared which, together with the first crop, gives a 55% total recovery of microsomal markers. 87% of the protein in this second crop also originates from the endoplasmic reticulum and this fraction has properties similar to those of the first crop. Contaminating membranes include Golgi membranes (0.6% of the total protein), mitochondria (2.5%), lysosomes (5%) and plasma membranes (5%). Collecting further crops increases the contamination. Subfractionation studies revealed almost identical distributions of ribosome-rich, ribosome-poor and smooth membranes in the two crops of microsomal fractions. The results obtained after treatment of the animals with phenobarbital or methylcholantrene were similar to those obtained with control animals; but in the case of methylcholantrene treatment the second crop represents a larger portion of the total membranes of the endoplasmic reticulum.

The topology of epoxide hydratase and benzpyrene monooxygenase in the endoplasmic reticulum of rat liver.

The distributions of benzpyrene monooxygenase and epoxide hydratase in subfractions of liver microsomes from control and from phenobarbital- and methylcholanthrene-treated rats have been investigated. The specific activities of these enzymes in rough and smooth microsomes from control and phenobarbital-treated animals are approximately the same, whereas after methylcholanthrene treatment benzpyrene monooxygenase is four times higher and epoxide hydratase twice as high in the rough vesicles. Further subfractionation of rough and smooth microsomes by rate differential centrifugation revealed the distributions of both enzymes among microsomal vesicles to be highly heterogeneous. Comparison of these distributions leads to the conclusion that the benzpyrene monooxygenase system and epoxide hydratase may form a complex of unique stoichiometry in the membrane of microsomes from control rats, but that such a complex is not consistent with the distributions obtained after methylcholanthrene induction. Studies with proteases and the nonpenetrating chemical reagent diazobenzene sulfonate suggest that epoxide hydratase may be buried deeply in the hydrophobic phase of the membrane of the hepatic endoplasmic reticulum.

Isolation of ribose-poor rough microsomes from rat liver

The rough microsomal fraction of the rat liver is the site of synthesis of newly appearing enzymes and membrane components in the newborn, phenobarbitaland alloxan-treated rats [ 1, 21 . It also synthesizes enzymes for other subcellular particles [3] and performs the complete or partial biosynthesis of most of the blood proteins [4-61. During membrane biosynthesis, an increasing “spacing” among ribosomal groups is apparent on electronmicroscopical investigation, which raises the possibility that membrane growth, including the incorporation of constitutive microsomal enzymes, occurs in specific parts of the endoplasmic reticulum [7] . In order to approach this problem, we elaborated a method which enabled us to separate rough microsomal vesicles with only a few attached ribosomes. The procedure is based on the decreased sensitivity of these vesicles to monovalent cations which specifically aggregate rough microsomes. centrifuge tube was subdivided by using a bent needle connected to a syringe. The centrifuge tube was placed on a variable stand so that it could be raised to the exact height required. The clear upper phase was discarded, and the fluffy double layer at the gradient boundary was removed and designated smooth microsomes (Sm). The 1.3 M sucrose layer down to the upper edge of the pellet was sucked off (rough III microsomes, R III). The remaining sucrose solution was taken up with a Pasteur pipette (rough II microsomes, R II), and the pellet was suspended in 0.25 M sucrose (rough I microsomes, R I). Smooth, R II and R III microsomes were supplemented with water or sucrose to obtain a final concentration of 0.25 M sucrose, and after centrifugation at 105,000 g for 90 min the pellets were resuspended in 0.25 M sucrose. The washing of subfractions and the chemical and enzyme assays were performed as described previously [7-111.

The crystal structure of room-temperature synthesised orthorhombic TlCu4Se3 from direct methods on X-ray powder data

An orthorhombic modification of TlCu4Se3 was synthesised at room temperature by oxidative copper extraction from TlCu5Se3. It crystallises in a new structure type, space group Pnnm, with the cell parameters a = 12.4306(2) A, b = 12.7997(2) A, c = 3.93516(6) A. The structure is closely related to the tetragonal structure of the parent compound. For the structure solution direct methods were used on single-phase Guinier-Hagg X-ray powder film data. In the refining stage, the Rietveld method was applied on powder diffractometer data. After being heated above 670 K, this orthorhombic form completely transforms to the tetragonal modification. Both are metallic conductors.

Lateral Enzyme Topology in the Rough Endoplasmic Reticulum of Rat Liver

SummaryRough microsomes were subfractionated on the basis of different properties in order to investigate the nature and extent of the enzyme heterogeneity of these vesicles. A discontinuous gradient, containing monovalent cations allowed the separation of a ribosome-poor membrane fraction which was enriched in electron transport enzymes and relatively poor in phosphatases. Zonal centrifugation on a stabilizing gradient separated 3 fractions characterized by enrichment of electron transport enzymes, glucose-6-phosphatase and adenosinetriphosphatase, respectively. An essentially similar pattern was seen when ribosomes were removed with EDTA and the denuded vesicles subfractionated on a sucrose gradient. Rough microsomes from phenobarbitaltreated rats exhibited the same pattern both qualitatively and quantitatively. It appears that electron transport enzymes and two types of phosphatases are heterogeneously distributed among rough microsomal vesicles.

Centrifugation of Liver Microsomes on Metrizamide Density Gradients

Abstract Metrizamide, 2-(3-acetamido-5-N-methyl-acetamido-2, 4, 6–triiodobenzamido)-2-deoxy-D-glucose (mol. wt 789), inhibits liver microsomal enzymes only to a small degree and it has no solubilization or detergent effects on the membrane. Four hour centrifugation in a continuous metrizamide gradient is sufficient for microsomal vesicles to attain equilibrium. This medium penetrates freely the intramicrosomal water space and, as a result of a possible increase in hydration water, rough microsomes are recovered mainly in 1.14–1.19 g/cm3, and smooth microsomes in the 1.08–1.13 g/cm3 density regions. It appears that metrizamide gradients are very advantageous for density gradient centrifugation of microsomal fraction.

A reinterpretation of the NH4Cu7S4 structure

Abstract The structure of NH 4 Cu 7− x S 4 has been investigated using X-ray single crystal diffraction at varying temperatures. The room temperature structure is best described as a tetragonal crystalline framework with channels incorporating some of the copper atoms in a disordered, almost amorphous, manner. The crystallographic description based primarily on the framework renders the space group I 4/ m and a unit cell with a =10.2695(5) A and c =3.8094(3) A. Upon cooling below 270 K, the copper atoms in the channels start to order. To begin with, the compound adopts the CsAg 7 S 4 structure type with the unit-cell parameters a =10.289(1) A and c =7.704(1) A. Upon further cooling, incommensurate orderings occur, in accordance with the fact that a copper deficient sample was used in the investigation ( x ≈0.16).