Allosteric Modulation of [3H]CGP 39653 Binding by Glycine in Rat Brain

Abstract: D,L-(E)-2-Amino-4-propyl-5-phosphono-3-pen-tenoic acid (CGP 39653). a new, high-affinity, selective NMDA receptor antagonist, interacts with rat cortical membranes in a saturable way and apparently to a single binding site, with a K_D of 10.7 nM and a receptor density of 2.6 pmol/mg of protein. Displacement analysis of [³H]CGP 39653 binding shows a pharmacological profile similar to that reported for another NMDA antagonist, 3-[(±)-2-carboxypiperazin-4-yI]propyl-1-phosphonic acid (CPP). Glycine, however, is able to discriminate between the two ligands; in fact, it does not affect [³H]CPP binding but inhibits [³H]CGP 39653 binding in a biphasic way. D-Serine, another agonist at the strychnine-insensitive glycine binding site of the NMDA receptor complex, inhibits [³H]CGP 39653 binding in the same way as glycine, with a potency that correlates with its binding affinity at the glycine site. In addition, 7-chlorokynurenic acid, an antagonist at the glycine site, is able to reverse the displacement of [³H]CGP 39653 by glycine in a dose-dependent manner. Furthermore, the dissociation rate constant of [³H]CGP 39653 is enhanced in the presence of glycine, whereas the presence of NMDA receptor ligands does not modify the rate of dissociation of [³H]CGP 39653 from the receptor. These results indicate that part of the binding of the NMDA antagonist CGP 39653 can be potently modified by glycine through an allosteric mechanism, and suggest the existence of two antagonist preferring NMDA receptor subtypes that are differentially modulated through the glycine binding site.     

Increased removal capacity for 1,2-dichloroethane by biological modification of the granular activated carbon process

The removal of 5 mg 1^–1 1,2-dichloroethane [(CH₂Cl)₂] was studied in two granular activated carbon (GAC) reactors run with hydraulic retention times of below 1 h. One reactor was operated abiotically. The other one was inoculated with microorganisms able to degrade (CH₂Cl)₂. While the (CH₂Cl)₂-adsorption capacity of the non-inoculated GAC reactor was exhausted after 20 days, it apparently did not exhaust for at least 170 experimental days in the biologically activated system because (CH₂Cl)₂ was removed to over 95% as a result of the microbial degradation. The biodegradation was quantified: during the passage through the biologically activated GAC reactor, (CH₂Cl)₂ (5± mg l^–1) disappeared, chloride ions (3.3±0.2 mg l^–1) were produced, and oxygen (4 to 6 mg l^–1) was consumed. Removal of 30% of GAC at the entrance of the reactor, which visibly carried most of the biomass, and its replacement by virgin GAC at the end of the column did not change the apparent (CH₂Cl)₂removal capacity of the GAC column, indicating that still enough biomass was available to degrade most of the chemical fed. After the addition of the virgin carbon, the effluent concentration fell for a short period of time from about 200 g l^–1 to below 100 g l^–1, indicating partial adsorption of the non-degraded (CH₂Cl)₂ at the end of the reactor by the virgin carbon. Thus, the modification of the adsorption process by inoculation and maintenance of bacteria with special degradation capabilities resulted in a lower consumption of GAC and thus led to an extended service life of the GAC columns.     

Growth promotion by homocysteine thiolactone and its alpha-alkylated derivative — A role for excess growth in homocystinurias?

Summary It is controversial whether homocysteic acid or other homocysteine derivatives show growth promoting effects. In a clonogenic assay we could show that homocysteine thiolactone and its alpha alkylated derivative increased colony formation significantly. Our work favorizes previous observations showing growth promoting activity of homocysteine derivatives and encourages further studies on that subject with implications for growth in physioogy and under pathological conditions.     

Production of β-1,3-glucanase from Trichoderma harzianum in surface and submerged culture processes and its role on protoplast generation from Trichoderma reesei mycelium

Surface and submerged culture studies were carried out for the production of extracellular -1,3-glucanase and carboxymethylcellulase from Trichoderma harzianum, NCIM 1185. The different parameters which influence the enzyme production, viz., spore age in the slant growth, seed age, and pH (initial) of the production medium have been optimized. The ranges of these parameters studied were: Spore age of T. harzianum between 2 and 10 days, seed age between 12 h and 48 h, and pH (initial) between 3 and 7. The other conditions of fermentation were: Temperature 30°C, gyratory shaker speed 160 rev. min^–1. It was observed that the activities of -1,3-glucanase and carboxymethylcellulase varied during the entire fermentation cycle which had a distinct effect on protoplast generation from T. reesei mycelium. The optimum values of the above-mentioned parameters for lytic enzymes production were: Spore age of T. harzianum in the slant growth 5 days, seed age 36 h, and pH (initial) 5.0 for both surface and submerged culture processes.Mr. S. Venkatesan, Department of Chemical Engineering, is thanked for his excellent secretarial help.     

Acide abscissique lié et dormance embryonnaire chez Pyrus malus

Bound abscisic acid and embryo dormancy in Pyrus malus. The first part of this work was devoted to the study of the behaviour of Pyrus malus L. cv. Golden Delicious embryos cultivated in vitro. At the beginning of the experiment, either the root (RM) or the distal part of the cotyledons (CM) was immersed in the medium. For embryos directly isolated from the fruits at harvest time, as well as for embryos submitted to a 3-month post-maturation treatment at 4°C, the dormancy was deeper in CM cultures than in RM. The use of gibberellins (GA₄ or GA₇) emphasized these differences. The second part of this work was devoted to the study of free and bound forms of ABA (cis and trans isomers) in embryos isolated from the fruits at harvest time and cultivated by the RM or CM procedure during 3 weeks. The biochemical data obtained indicated in both cases the existence of the following three processes: (A) Mobilization of the bound ABA with the consequent release of free ABA; this was particularly important in CM. (B) Metabolism of free ABA: the isomerization into trans-ABA only partly accounted for the decrease in the content of free ABA which was much greater in RM than in CM. (C) Transport of ABA towards the root, the result being an accumulation of free ABA in the root, much greater in CM than in RM; this would account for the deeper dormancy in CM than in RM.     

Cell yields of Escherichia coli during anaerobic growth on fumarate and molecular hydrogen

Escherichia coli was grown anaerobically on sodium fumarate and molecular hydrogen or sodium formate in continuous culture. The maximal growth yield and the maintenance coefficient were determined. In a mineral medium a Y _fum ^max value of 6.6 g dry weight per mol fumarate was found. This value increased to 7.5 when casamino acids were present in the medium. From these data and the corresponding Y _ATP ^max values it could be calculated that per mol of fumarate reduced, 0.4 mol of ATP became available for growth. In batch culture a Y_fum value of 4.8 g dry weight per mol fumarate was determined.     

The coding site of chloroplast ferredoxin

Ferredoxins were isolated and purified from leaves of different species of Nicotiana and Petunia and from spinach leaves. Their spectral properties, degree of homogeneity, and molecular weights were determined. The preparations were further analyzed by polyacrylamide gel electrophoresis of tryptic hydrolysates. This allowed us to distinguish between not only ferredoxins of Nicotiana, Petunia, and spinach, but even ferredoxins of various Nicotiana species. We used the differences in tryptic peptide compositions as phenotypic markers to study the mode of inheritance of chloroplast ferredoxin to see whether the coding site is in the chloroplast or in the nucleus. Analysis of the tryptic peptide composition of ferredoxin from different interspecific hybrids of Nicotiana showed that the characteristics of both parental ferredoxins were present. The results indicate that the primary structure of at least the male ferredoxin is coded for in the nucleus. In some of the hybrids the relative contribution of the male parent appeared to be low, suggesting that the female genome (presumably that part located in the plastome) exerted a dominating influence.     

Immunosuppressive factor(s) specific for L-glutamic acid50-L-tyrosine50 (GT). I. Production, characterization, and lack of H-2 restriction for activity in recipient strain.

The random synthetic copolymer of L-glutamic acid50-L-tyrosine50 (GT) fails to elicit a GT-specific antibody response in all inbred strains of mice tested. Preimmunization with GT specifically inhibits a GT-MBSA response in certain H2d,k,s, but not other, H-2a,b,q, nonresponder mice. This unresponsiveness is mediated by GT-specific suppressor T cells. Extracts prepared from lymphoid cells of GT-primed suppressor haplotype mice inhibit the development of primary GT-specific antibody responses to GT-MBSA in normal syngeneic mice. Nonsuppressor haplotype mice do not produce GT-specific suppressor factor. The GT-suppressive extract has affinity for antigen and a m.w. of less than 50,000 daltons, thus, resembling antigen-specific immunosuppressive factors already described. However, the GT-suppressive extract does not appear to have H-2 restrictions since it works across allogeneic barriers. Evidence is presented that two genes are required for factor-mediated suppression.