Characterization of a biologically active arabinogalactan from the leaves of Plantago major L.

PMIa is a Type II arabinogalactan with anti-complementary activity isolated from the leaves of Plantago major L. It has a molecular weight of 77000–80000 Da and consists of arabinose (38%), galactose (49%), rhamnose (6%), galacturonic acid (7%) and 1.5% protein with hydroxyproline, alanine and serine as the main amino acids. Characterization of PMIa by methylation and GC-MS, methanolysis and GC, Smith degradation, weak acid hydrolysis, ¹³C-NMR, ¹H-NMR, two-dimensional heteronuclear NMR and DEPT show that it consists of 1,3-linked galactan chains with 1,6-linked galactan side chains attached to position 6. The side chains are further branched in position 3 with 1,3-linked galactose residues which have 1,6-linked galactose attached to position 6; these 1,3- and 1,6-linked galactose chains altogether probably form a network. Terminal and 1,5-linked arabinose in furanose form are attached to the galactan mainly through position 3 of the 1,6-linked galactose side chains.     

Modulation of membrane drug permeability in Chinese hamster ovary cells

The kinetics of colchicine uptake into Chinese hamster ovary cells have been investigated and found to be consistent with an unmediated diffusion mode. A variety of compounds such as local anesthetics and non-ionic detergents as well as drugs such as vinblastine, vincristine, daunomycin and actinomycin D potentiate the rate of colchicine uptake into these cells and into colchicine resistant mutants. In all cases, higher concentrations of these compounds were required to stimulate colchicine uptake in the colchicine resistant mutants than in the cells of the parental line. This stimulation was observed also in the uptake of puromycin, a structurally and functionally different drug. These stimulatory agents did not, however, cause the cells to become nonspecifically leaky since the uptake of 2-deoxy-d-glucose was unaffected. In addition, the activation energy of colchicine uptake was unaltered in the presence of stimulating agents, implying that they were not causing colchicine to enter the cells via a different mechanism. The results are compatible with the view that these compounds are membrane-active, and are able to stimulate an increased rate of unmediated diffusion of colchicine into the cells. It appears that a mechanism for the regulation of passive permeability is modified in the resistant mutants.     

The Liver of Myxine glutinosa: A true tubular gland

Summary The authors have reexamined the liver of Myxine with the light and electron microscopes. The observations demonstrate that the liver in this animal is really a tubular gland, in accordance with the conclusions of older anatomists, but in contrast to more recent statements. The existence of a tubular pattern in the liver of the lowest living vertebrate is important for the elaboration of a valid general model of liver structure, which necessarily has to be based on comparative anatomy.The special cytology of the liver and the ductular cells is presented.     

Icreased drug permeability in Chinese hamster ovary cells in the presence of cyanide

In this report we investigated whether the modulation of drug permeability in Chinese hamster ovary (CHO) cells was an energy-dependent process. We observed that (1) in the absence of glucose, metabolic inhibitors such as cyanide, azide, and dinitrophenol stimulated the uptake of [³H]colchicine and other drug; (2) cyanide-induced stimulation of drug uptake could be prevented by the presence of metabolizable sugars such as glucose and ribose; (3) cyanide-treated cells were fully viable; (4) on the addition of cyanide and glucose the kinetics of drug permeability changes were very rapid. These data are consistent with the hypothesis that an energy-dependent membrane barrier against the uptake of a variety of drugs was operative in CHO cells.The nature of this energy-dependent membrane barrier was examined in colchicine-resistant mutants (CH^RC4 and CH^RC5 cells) previously characterized as membrane mutants with greatly reduced drug permeability (Ling and Thompson, (1974) J. Cell Physiol. 83, 103–116). The mutants were more refractile to the cyanide-induced stimulation of drug permeability but more sensitive to the glucose prevention cyanide-induction. In the presence of cyadine, the uptake rate of [³H] colchicine by CH^RC4 cells increased by about 100-fold and approached a rate similar to that of wild-type cells. These results suggest that the colchicine-resistant mutants may be altered in their energy-dependent modulation of drug permeability.     

Properties and action pattern of the recombinant mannuronan C-5-epimerase AlgE2

The mannuronan C-5-epimerase AlgE2 is one of a family of Ca²⁺-dependent epimerases secreted by Azotobacter vinelandii. These enzymes catalyze the conversion of β- -mannuronic acid residues (M) to - -guluronic acid residues (G) in alginate. AlgE2 has been produced by fermentation with a recombinant strain of Escherichia coli, isolated and partially purified. Epimerization with AlgE2 increased the content of G-residues in different alginates from starting values of 0–45% up to approximately 70%. The new G-residues were mainly present in short blocks. Although G-residues may be introduced next to pre-existing G-residues, AlgE2 was not able to epimerize strictly alternating MG-structures. The epimerization with AlgE2 was greatly affected by the concentration of Ca²⁺. The type of alginate used as substrate affected the reaction rate and the reaction pattern especially at low Ca²⁺ concentration. AlgE2 appears to act by a preferred attack mechanism where the enzyme associates with different sequences in the alginate depending on the concentration of Ca²⁺. During epimerization, AlgE2 occasionally causes cleavage of the alginate chain. The observed frequency corresponds to 1–3 breaks per 1,000 M-units epimerized.     

Focus: Rare Disease: Psychosocial Functioning in Siblings of Children With Rare Disorders Compared to Controls

Siblings of children with chronic disorders are at increased risk of psychosocial problems. The risk may be exacerbated when the chronic disorder is rare and limited medical knowledge is available, due to more uncertainty and feelings of isolation. We examined mental health, parent-child communication, child-parent relationship quality, and social support among 100 children aged 8 to 16 years (M age 11.5 years, SD = 2.2; 50.0% boys, 50.0% girls). Fifty-six were siblings of children with rare disorders, and 44 were controls. The siblings of children with rare disorders (herein, siblings) were recruited from a resource centre for rare disorders and comprised siblings of children with a range of rare disorders including neuromuscular disorders and rare chromosomal disorders with intellectual disability. Controls were recruited from schools. Self-reported child mental health was significantly poorer for siblings compared to controls (effect size difference d = 0.75). Parent-reported child mental health was not significantly different between the groups (d = -0.06 to 0.16). Most child-parent relationships (anxiety/avoidance; mothers/fathers) were significantly poorer for siblings compared to controls (d = 0.47 to 0.91). There was no difference between groups in anxious relation with mother. Parent-child communication was significantly poorer for siblings compared to controls (d = -0.87 to -0.75). Social support was significantly poorer for siblings compared to controls (d = 0.61). We conclude that siblings of children with rare disorders display more psychosocial problems than controls. Interventions are indicated to prevent further maladjustment for siblings.