X-ray Studies on Crystalline Complexes Involving Amino Acids and Peptides. XIII. Effect of Chirality on Molecular Aggregation: The Crystal Structures of L-Arginine D-Aspartate and L-Arginine D-Glutamate Trihydrate

The crystal structures of (1) L-arginine D-asparate, C6HIsN40~.C4H6NO4 [triclinic, P1, a=5.239(1), b=9.544(1), c=14.064(2)A, a=85"58(1), /3=88.73 (1), ~/=84.35 (1) °, Z=2] and (2) L-arginine D-glutamate trihydrate, C6H15N40~-.CsHsNO4.3H20 [monoclinic, P2~, a=9.968(2), b=4.652(1), c=19.930 (2) A, fl = 101.20 (1) °, Z = 2] have been determined using direct methods. They have been refined to R =0.042 and 0.048 for 2829 and 2035 unique reflections respectively [I>2cr(I)]. The conformations of the two arginine molecules in the aspartate complex are different from those observed so far in the crystal structures of arginine, its salts and complexes. In both complexes, the molecules are organized into double layers stacked along the longest axis. The core of each double layer consists of two parallel sheets made up of main-chain atoms, each involving both types of molecules. The hydrogen bonds within each sheet and those that interconnect the two sheets give rise to EL-, DD- and DE-type head-to-tail sequences. Adjacent double layers in (1) are held together by side-chain-side-chain interactions whereas those in (2) are interconnected through an extensive network of water molecules which interact with sidechain guanidyl and carboxylate groups. The aggregation pattern observed in the two LD complexes is fundamentally different from that found in the corresponding EL complexes.

Studies on nucleotidases in plants : Reversible denaturation of the crystalline mung bean nucleotide pyrophosphatase and the effect of adenylates on the native and renatured enzyme

The crystalline mung bean nucleotide pyrophosphatase was inhibited nonlinearly by AMP, one of the products of the reaction. The partially inactive enzyme was specifically reactivated by ADP, and V at maximal activation was the same as that of the native enzyme. ATP was a linear, noncompetitive inhibitor. The kinetic evidence suggested that ADP and ATP might not be reacting at the same site as AMP. The electrophoretic mobility of the enzyme was increased by AMP, whereas ADP and ATP were without effect. The enzyme was denatured on treatment with urea or guanidine hydrochloride. The renatured and the native enzyme had the same pH (9.4) and temperature (49 °C) optimum. The Km (0.2 mImage ) and V (3.2) of the native enzyme increased on renaturation to 1.8 mImage and 8.0, respectively. In addition, renaturation resulted in desensitization of the enzyme to inhibition by low concentrations of AMP. Renaturation did not affect the reactivation of the apoenzyme by Zn2+.

Studies on nucleotidases in plants - Reversible denaturation of the crystalline mung bean nucleotide pyrophosphatase and the effect of adenylates on the native and renatured enzyme

The crystalline mung bean nucleotide pyrophosphatase was inhibited nonlinearly by AMP, one of the products of the reaction. The partially inactive enzyme was specifically reactivated by ADP, and V at maximal activation was the same as that of the native enzyme. ATP was a linear, noncompetitive inhibitor. The kinetic evidence suggested that ADP and ATP might not be reacting at the same site as AMP. The electrophoretic mobility of the enzyme was increased by AMP, whereas ADP and ATP were without effect. The enzyme was denatured on treatment with urea or guanidine hydrochloride. The renatured and the native enzyme had the same pH (9.4) and temperature (49 °C) optimum. The Km (0.2 m ) and V (3.2) of the native enzyme increased on renaturation to 1.8 m and 8.0, respectively. In addition, renaturation resulted in desensitization of the enzyme to inhibition by low concentrations of AMP. Renaturation did not affect the reactivation of the apoenzyme by Zn2+.

Nucleotidases in plants *1, , *2: III. Effect of metabolites on the enzyme hydrolyzing flavine adenine dinucleotide (FAD) from Phaseolus radiatus

The highly purified enzyme from mung bean seedlings hydrolyzing FAD at pH 9.4 and temperature 49 °, functioned with an initial fast rate followed by a second slower rate. The activity was linear with enzyme concentration over a small range of concentration and was dependent on the time of incubation. Inhibition of enzyme activity with increasing concentrations of AMP was sigmoid;concentrations less than 1 × 10−6 M were without effect, concentrations between 1 × 10−6 and 8 × 10−5 M inhibited by 20% and concentrations beyond 8 × 10−5 Image caused progressive inhibition. Concentrations beyond 1 × 10−3 Image inhibited the activity completely. Preincubation of the enzyme with PCMB or NEM, or aging, or reversible denaturation with urea abolished the inhibitory effect of AMP at concentrations lower than 8 × 10−6 Image . The aged enzyme could be reactivated by ADP.

X-ray studies on crystalline complexes involving amino acids and peptides. XV. Crystal structures of L-lysine D-glutamate and L-lysine D-aspartate monohydrate and the effect of chirality on molecular aggregation

L-Lysine D-glutamate crystallizes in the monoclinic space group P2(1) with a = 4.902, b = 30.719, c = 9.679 A, beta = 90 degrees and Z = 4. The crystals of L-lysine D-aspartate monohydrate belong to the orthorhombic space group P2(1)2(1)2(1) with a = 5.458, b = 7.152, c = 36.022 A and Z = 4. The structures were solved by the direct methods and refined to R values of 0.125 and 0.040 respectively for 1412 and 1503 observed reflections. The glutamate complex is highly pseudosymmetric. The lysine molecules in it assume a conformation with the side chain staggered between the alpha-amino and the alpha-carboxylate groups. The interactions of the side chain amino groups of lysine in the two complexes are such that they form infinite sequences containing alternating amino and carboxylate groups. The molecular aggregation in the glutamate complex is very similar to that observed in L-arginine D-aspartate and L-arginine D-glutamate trihydrate, with the formation of double layers consisting of both types of molecules. In contrast to the situation in the other three LD complexes, the unlike molecules in L-lysine D-aspartate monohydrate aggregate into alternating layers as in the case of most LL complexes. The arrangement of molecules in the lysine layer is nearly the same as in L-lysine L-aspartate, with head-to-tail sequences as the central feature. The arrangement of aspartate ions in the layers containing them is, however, somewhat unusual. Thus the comparison between the LL and the LD complexes analyzed so far indicates that the reversal of chirality of one of the components in a complex leads to profound changes in molecular aggregation, but these changes could be of more than one type.

Studies on the Mechanism of Action of Miconazole: Effect of Miconazole on Respiration and Cell Permeability of Candida albicans

The antifungal drug, miconazole nitrate, inhibits the growth of several species of Candida. Candida albicans, one of the pathogenic species, was totally inhibited at a concentration of approximately 10 μg/ml. Endogenous respiration was unaffected by the drug at a concentration as high as 100 μg/ml, whereas exogenous respiration was markedly sensitive and inhibited to an extent of 85%. The permeability of the cell membrane was changed as evidenced by the leakage of 260-nm absorbing materials, amino acids, proteins, and inorganic cations. The results we present clearly show that the drug alters the cellular permeability, and thus the exogenous respiration becomes sensitive to the drug.

Studies on the Mechanism of Action of Miconazole: Effect of Miconazole on Respiration and Cell Permeability of Candida albicans

The antifungal drug, miconazole nitrate, inhibits the growth of several species of Candida. Candida albicans, one of the pathogenic species, was totally inhibited at a concentration of approximately 10 µg/ml. Endogenous respiration was unaffected by the drug at a concentration as high as 100 µg/ml, whereas exogenous respiration was markedly sensitive and inhibited to an extent of 85%. The permeability of the cell membrane was changed as evidenced by the leakage of 260-nm absorbing materials, amino acids, proteins, and inorganic cations. The results we present clearly show that the drug alters the cellular permeability, and thus the exogenous respiration becomes sensitive to the drug.

Effect of lipopolysaccharide on alteration of phospholipids and their fatty acid composition in spleen and thymus by in vitro metabolic labeling

Lipopolysaccharide (LPS) is an endotoxin, a potent stimulator of immune response and induction of LPS leads to acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). ARDS is a life-threatening disease worldwide with a high mortality rate. The immunological effect of LPS with spleen and thymus is well documented; however the impact on membrane phospholipid during endotoxemia has not yet been studied. Hence we aimed to investigate the influence of LPS on spleen and thymus phospholipid and fatty acid composition by 32P]orthophosphate labeling in rats. The in vitro labeling was carried out with phosphate-free medium (saline). Time course, LPS concentration-dependent, pre- and post-labeling with LPS and fatty acid analysis of phospholipid were performed. Labeling studies showed that 50 mu g LPS specifically altered the major phospholipids, phosphatidylcholine and phosphatidylglycerol in spleen and phosphatidylcholine in thymus. Fatty acid analysis showed a marked alteration of unsaturated fatty acids/saturated fatty acids in spleen and thymus leading to immune impairment via the fatty acid remodeling pathway. Our present in vitro lipid metabolic labeling study could open up new vistas for exploring LPS-induced immune impairment in spleen and thymus, as well as the underlying mechanism.

The effect of pH on the unfolding pathway and stability of ribosome-inactivating protein abrin-II

The effect of pH on the unfolding pathway acid the stability of the toxic protein abrin-II have been studied by increasing denaturant concentrations of guanidine hydrochloride and by monitoring the change in 8,1-anilino naphthalene sulfonic acid (ANS) fluorescence upon binding to the hydrophobic sites of the protein. Intrinsic protein fluorescence, far and near UV-circular dichroism (CD) spectroscopy and ANS binding studies reveal that the unfolding of abrin-II occurs through two intermediates at pH 7.2 and one intermediate at pH 4.5. At pH 7.2, the two subunits A and B of abrin-II unfold sequentially. The native protein is more stable at pH 4.5 than at pH 7.2. However, the stability of the abrin-II A-subunit is not affected by a change in pH. These observations may assist in an understanding of the physiologically relevant transmembrane translocation of the toxin.

Soft-particle model analysis of effect of LPS on electrophoretic softness of Acidithiobacillus ferrooxidans grown in presence of different metal ions

The effect of Surface lipopolysaccharides (LPS) on the electrophoretic softness and fixed charge density in the ion-penetrable layer of Acidithiobacillus ferrooxidans cells grown in presence of copper or arsenic ions have been discussed, The electrophoretic mobility data were analyzed using the soft-particle electrophoresis theory. Cell surface potentials of all the strains based on soft-particle theory were lower than those estimated using the conventional Smoluchowski theory, Exposure to metal ions increased the Surface electrophoretic softness with decrease in the fixed charge density. Effect of cell surface lipopolysaccharides on the model parameters are investigated and discussed.

Effect of microstructure on the mechanical behavior of b-modified ti-6al-4v alloys

Small additions of B to Titanium alloys refine the as-cast microstructure significantly and hence improve their mechanical performance. In this work, tensile, fracture and fatigue properties of the as-cast and HIPed Ti-6Al-4V alloy with hypoeutectic wt.% of B additions have been examined, with particular emphasis on identifying the microstructural length scale that controls the mechanical properties of these alloys.

Effect of chlorine on the adsorption of oxygen on Cu and Ag surfaces

Based on XPS and UVPS studies, it is shown that oxygen is preferentially adsorbed molecularly in the singlet state on Cu and Ag surfaces containing presorbed chlorine. Adsorption of chlorine on Cu and Ag surfaces containing presorbed atomic oxygen causes a disappearance of the oxygen. Extended Hückel calculations predict the observed behaviour.

Effect of pressure on the electrical resistivity of indium sulphide

Indium sulphide (INS) is a III-VI compound semiconductor and crystallizes in the orthorhombic structure with a space group D~(Pmnn). The lattice parameters at room temperature and atmospheric pressure are: a = 3.944 A, b = 4.447 A and c= 10.648#, [1, 2]. The crystal structure comprises an ethane-like SalnlnS3 atomic arrangement;the SalnInS3 groups are mutually linked by sharing S corners and form a three-dimensional network.

Effect of pressure on the resistivity of lead oxide-lead halide glasses

Resistivity behaviour of PbO---PbX2 (X=F,Cl) glasses has been investigated as a function of pressure at laboratory temperature. All PbO---PbX2 glasses undergo crystallization under pressure and the resistivities of crystallized samples are lower than the corresponding glasses. Transitions in PbO---PbF2 glasses exhibit a first order behaviour while transitions in PbO---PbCl2 glasses possess features of a continuous transition. The differences in the pressure behaviour of the two glass systems have been attributed to the differences in the ionic sizes of F− and Cl− ions and also to pressure induced modifications of Pb---O bonding.

Effect of radiation on the Peierls transition

The effect of radiation on the Peierls transition in a one-dimensional metal is investigated. It is pointed out that an external radiation field satisfying appropriate frequency conditions reduces the width of the Peierls gap.