Effects of exogenous soluble dextrans on insoluble glucan synthesis by Streptococcus mutans glucosyltransferase

Production of water-insoluble glucan (ISG) from sucrose by cell-free Streptococcus mutans AHT glucosyltransferase (GTF) first rapidly increased, and then sharply declined, as the amounts of water-soluble Dextrans T20 approximately T500 present, were increased. The decline of ISG synthesis was accompanied by an increased synthesis of the water-soluble fraction (SG). Prolonged incubation, however, induced enhanced synthesis of ISG even at higher dextran concentrations. The concentration of dextran required to stimulate or suppress ISG synthesis depended on the amounts of GTF used, but the extent of the stimulation was almost identical for the same GTF/dextran ratio. Thus, ISG synthesis is stimulated by the presence of dextrans at relatively low concentrations, but retarded at higher concentrations by being shifted to SG synthesis. ISG produced in the presence of dextrans contained higher proportions of alpha-1,6 glucosidic linkage and lower molecular size fractions, and possessed lower viscosity. These ISG products did not exhibit the coalescence of two component fibrils as observed with control ISG. These changes combined may contribute to the reduction of ISG-dependent adherence to glass of S. mutans cells by the presence of soluble dextrans, irrespective of their molecular size and concentration.     

An X-ray study on the interaction between indole ring and pyridine coenzymes: Crystal structure of 1-methyl-3-carbamoylpyridinium: Indole-3-acetic acid (1:1) monohydrate charge-transfer complex

The crystal and molecular structures of the title complex has been determined by X-ray diffraction methods, as a model for tryptophan residues in protein-pyridine coenzyme interactions. The structure was solved by direct methods and was refined by standard methods (final R = 0.073). The light-green crystals consist of alternate layers of indole-3-acetic acid and 1-methyl-3-carbamoylpyridinium molecules piled up to the c-direction, and are stabilized by the crystal water participating in hydrogen bonds in the a- and b-directions. The parallel stackings and interplanar spacing distances between indole and pyridinium rings strongly suggest a II–II¹ charge transfer from the indole ring to the lowest unoccupied orbital of the pyridinium ring in the ground state. Furthermore, this crystal structure provides evidence that quaternization of the N1 position enhances electron-acceptor properties of pyridine. On the other hand, the proton magnetic resonance spectra suggest that the stacking mode between both rings in solution is very similar to the one observed in the crystal structure.     

13C and 1H NMR studies of helix-coil transition of poly(β-benzyl-L-aspartate) and poly(γ-benzyl-L-glutamate): Behavior in nonprotonating solvent mixtures,and origin of solvent-induced chemical shift

From the results of ¹³C-nmr measurement of poly(β-benzyl-L -aspartate) and its model compounds in dimethyl sulphoxide/deuterated chloroform mixtures, it was found that the side chain of poly(β-benzyl-L -aspartate) is solvated by dimethyl sulphoxide in the region more than dimethyl sulphoxide 20% (v/v), where the backbone maintains the α-helix. The chemical shift differences in the benzyl group carbons of poly(γ-benzyl-L -glutamate) (trifluoroacetic acid/deuterated chloroform) accompanied by the helix-coil transition, originate from the interaction between the ester group of the side chain and trifluoroacetic acid. The chemical shift difference in the ester carbon is similar. On the other hand, the chemical shift differences of the side-chain carbons in the alkyl portion (C^β, C^γ) originate not only from the interaction between the ester group of the side chain and trifluoroacetic acid, but also from some other unknown factors. The chemical shift differences of the side-chain carbons of poly(β-benzyl-L -aspartate) originate from the interaction between the ester group of the side chain and trifluoroacetic acid.     

Fast atom bombardment tandem mass spectrometric analysis of N-carbamoylamino acids.

Using fast atom bombardment (FAB) and tandem mass spectrometry (MS/MS), we examined 12 synthetic N-carbamoylamino acids (CAA) as tert-butyldimethylsilyl (TBDMS) derivatives. In FAB mass spectrometry and FAB MS/MS, spectra of protonated molecules for CAA provide specific cleavages involving the TBDMS carbamoyl moiety. The daughter scan spectrum of the parent ion indicated that it was useful for structural elucidation and differentiation of structural isomers of CAA. We have also identified each CAA separately in a mixture using a neutral loss scan for characteristic ions. In addition, we demonstrated that CAA in urine samples from patients with ornithine carbamoyl transferase deficiency gave collision-induced dissociation (CID) spectra which correspond well with CID spectra obtained using synthetically prepared CAA.     

Peptide transport by the multidrug resistance pump.

The membrane P-glycoprotein (P170) is an ATP-hydrolyzing transmembrane pump, and elevated levels of P170, due to higher expression with or without amplification of the multidrug resistance gene (mdr1), result in resistance to a variety of chemotherapeutic agents in mammalian cells. The function of the P170 pump has been proposed as a protection against toxic substances present in animal diets. Here we describe a Chinese hamster ovary cell line that was selected for resistance to a synthetic tripeptide, N-acetyl-leucyl-leucyl-norleucinal (ALLN). This ALLN-resistant variant shows the classical multidrug resistance (MDR) phenotype, including overexpression and amplification of the mdr1 gene. Additionally, a mouse embryo cell line overexpressing the transfected mdr1 gene is likewise resistant to ALLN. Our results demonstrate that P170 is capable of transporting peptides and raise the possibility that the mdr1 gene product or other MDR-like genes, present in the genome of mammalian cells, may be involved in secretion of peptides or cellular proteins as is the case with the structurally similar hylB and ste6 gene products of Escherichia coli and yeast, respectively.     

Calcium binding to phospholipid: structural study of calcium glycerophosphate.

To consider possible interaction of the phospholipid membrane with calcium ions, crystal structures of calcium dl-alpha- and beta-glycerophosphates (alpha- and beta-CaGs, respectively) were investigated by X-ray diffraction methods. After many attempts, relatively large single crystals of beta-CaG were prepared from the aqueous solution containing HCl, while crystals of CaHPO4.2H2O were obtained from alpha-CaG solution under the same crystallization conditions. The crystal structure of beta-CaG is orthorhombic with space group Pna2(1) and cell dimensions of a = 8.251(1), b = 13.038(3), c = 25.483 (10) A, V = 2741.5 (13) A3 and Z = 16 [four molecules (A to D) in an asymmetric unit]. Molecules of A to D took, as a whole, similar extended conformations, although A and B were different from C and D in the orientation about a glycerol C-C bond. Four independent beta-glycerophosphates commonly act as two types of bidentate ligands, where one is the coordination to the calcium ion by the glycerol O(1) and phosphate O(22) atoms, and the other by the phosphate O(22) and O(23) atoms, thus forming the calcium coordination of a distorted square plane, respectively. Each of four independent calcium ions forms the same coordination geometry of a distorted pentagonal bipyramid. Infinite double layers consisting of alternate A/B molecules and of alternative C/D ones and sandwiching calcium ions were arranged face-to-face along the b-direction and were piled up in the a-direction, thus forming the stacked bilayer unit with the thickness of d002 = 12.75 A. The elaborate networks of calcium coordinations and hydrogen bondings were formed among the layers and stabilized the crystal structure. Based on the structural parameters of the present beta-CaG crystal, a possible interaction model of phospholipid with calcium ions was proposed.     

The hypnogenic effects of delta sleep-inducing peptide (DSIP) analogs: a comparative study in rabbits and rats]

Hypnogenic effects of 3 DSIP analogs with a higher stability against aminopeptidase activity have been studied in rabbits and rats using intraventricular administration (injections and infusions). An analog (D-Ala-2) DSIP augmented slow wave and paradoxical sleep within the 5th, 8th and 11th hours of the recording period. An analog (D-Val-2) DSIP made the same within the 8th and 10th hours, and hexapeptide (D-Ala-2) DSIP (1-6) increased sleep during the 1st, 3rd, and 5th hours. Both nonapeptides augmented sleep in rabbits as well as in rats, though hexapeptide produced this effect in rabbits only, that might be related to some difference in distribution and colocalization of endogenous DSIP-like peptide in the pituitary of two rodent species. It may be suggested that hypnogenic activity of DSIP analogs is determined by the structure of administrated molecule, being mediated by such hormones as GRF and CLIP.     

Somatostatin inhibits the nicotinic receptor-activated inward current in guinea pig chromaffin cells.

At a holding potential of -60 mV, bath application of somatostatin produced no current response itself, but inhibited the nicotinic inward current, a concentration of about 0.01 microM being required for a half-maximal effect. This inhibition was affected neither by pretreatment with somatostatin nor by injection of guanosine-5'-0-(3-thiotriphosphate) through a patch pipette. When somatostatin (0.03-0.1 microM) produced its maximum inhibition, the proportion of plateau to peak nicotinic current was greatly reduced (to 5.3 +/- 5.7% from the control value of 34.9 +/- 4.9%, n = 5) with a facilitation of the time course of desensitization. After washout of somatostatin, the nicotinic current was restored to control level in a time-dependent, rather than an activation-dependent manner. The results suggest that somatostatin inhibits the function of the nicotinic receptor by facilitation of its desensitization or by an open-channel block.     

X-ray crystallographic conformational study of 5'-O-[N-(L-alanyl)-sulfamoyl]adenosine, a substrate analogue for alanyl-tRNA synthetase

In order to elucidate the substrate specificity of alanyl-tRNA synthetase, 5'-O-[N-(L-alanyl)sulfamoyl]adenosine (Ala-SA), an analogue of alanyl-AMP, was chemically synthesized. Its binding ability is similar to that of the substrate based on the inhibitory activity for the aminoacylation of alanyl-tRNA synthetase. Taking advantage of the stable sulfamoyl bond of Ala-Sa, compared with the highly labile aminoacyl bond of alanyl-AMP, the molecular conformation of the former inhibitor was studied by X-ray single crystal analysis. Crystal data are as follows: C13H19N7O7S.2H2O, space group C2, a = 39.620(6), b = 5.757(1), c = 20.040(3) A, beta = 117.2(1) degrees, V = 4065(9) A3, Z = 8, and final R = 0.065 for 2785 independent reflections of F(2)0 greater than or equal to 2 sigma (F0)2. In the crystal, the molecule is in a zwitterionic state with the terminal amino group protonated and sulfamoyl group deprotonated, and takes an open conformation, where the L-alanine moiety is located far from the adenosine moiety with gauche/trans and trans orientations about the exocyclic C(4')-C(5') and C(5')-O(5') bonds, respectively. The conformation of the adenosine moiety is anti for the glycosyl bond and C(3')-endo for the ribose puckering, and alanine is in the usually observed trans region for the psi torsion angle. The molecular dimensions of the sulfamoyl group are nearly the same as those of the phosphate group. The biological significance of the observed Ala-SA conformation is discussed in relation with the molecular conformation of tyrosyl-AMP complexed with tyrosyl-tRNA synthetase.