The first vitamin B6 zinc complex, pyridoxinato-zinc acetate: A 1D coordination polymer with polar packing through strong inter-chain hydrogen bonding

The biologically important pyridoxinato(1−) ligand (anionic vitamin B₆) shows the rare phenolate-hydroxymethyl chelation plus bridging mode through the pyridine-nitrogen atom towards zinc(II) to give the one-dimensional (1D) coordination polymer {(acetato-κO)-aqua-μ-[2-methyl-3-oxy-4,5-di(hydroxymethyl)pyridine-κN:O,O′]zinc(II)}·monohydrate with polar packing of adjacent chains along the polar c axis (in space group Pc) through strong inter-chain hydrogen bonding.     

The effect of antibiotics on the photocycle and protoncycle of purple membrane suspensions

The interrelation was studied between the phototransient absorbing maximally at 412 nm (M₄₁₂) and light-induced proton release under steady-state conditions in aqueous suspensions of ‘purple membrane’ derived from Halobacterium halobium. The decay of M₄₁₂ was slowed down by the simultaneous application of the ionophoric antibiotics valinomycin and beauvericin. The former had only slight activity alone and the latter was effective only in conjunction with valinomycin. The steady-state concentration of M₄₁₂ which was formed on illumination was a direct function of the concentration of valinomycin. Maximum stabilization of M₄₁₂ was obtained when the valinomycin was approximately equimolar with the bacteriorhodopsin. Addition of salts to the medium increased the number of protons released per molecule of M₄₁₂ without affecting the level of M₄₁₂ which was produced by continuous illumination. The effectiveness of the salts in this respect depended on the nature of the cation. Ca²⁺ and their antagonists La³⁺ and ruthenium red were found to have especially high affinity for the system. The extent of light-induced acidification could not be enhanced by increasing the pH of the medium from 6.5 to 7.8. The possible mechanism of action of the ionophores and of the cations on the photocycle and on the proton cycle is discussed.     

X-ray absorption spectroscopy of selenium-containing amino acids

Received: 2 April 1999 / Accepted: 17 September 1999     

Ultrastructure of the developing pigment strand of rice (Oryza sativa L.) in relation to its role in solute transport

Summary The developing pigment strand of rice (Oryza sativa L.) was studied by conventional electron microscopy and also by use of thick sections post-fixed with zinc iodide and osmium (ZIO).When the rice caryopsis achieves maximum length, a suberised adcrusting wall layer is laid down over the original primary walls of the pigment strand. Concomitant with suberin deposition a proliferation of tubular endoplasmic reticulum occurs in the cytoplasm giving rise to numerous interconnected vesicles which bear ribosomes. The vesicles in the general cytoplasm retain their ribosomes while those close to the wall become smooth and contain an electron-opaque granular material which is eventually deposited to the outside of the plasmalemma. This granular material may be the precursor(s) from which suberin is polymerised. The suberised wall attains about six times the width of the original primary wall and plasmodesmata, which traverse both primary wall and suberised wall layers, become greatly elongated.Lipid bodies increase in both size and frequency during development, eventually coalescing to form a complete plug across the pigment strand and occluding the symplast of this tissue. The significance of these ultrastructural observations is discussed in relation to the previously demonstrated role of the pigment strand as a translocation pathway for water and assimilates during grain filling.Abbreviations ER endoplasmic reticulum - ZIO zinc iodide-osmium fixation     

Computational Oral Absorption Simulation for Low‐Solubility Compounds

Bile micelles play an important role in oral absorption of low‐solubility compounds. Bile micelles can affect solubility, dissolution rate, and permeability. For the pH–solubility profile in bile micelles, the Henderson–Hasselbalch equation should be modified to take bile‐micelle partition into account. For the dissolution rate, in the Nernst–Brunner equation, the effective diffusion coefficient in bile‐micelle media should be used instead of the monomer diffusion coefficient. The diffusion coefficient of bile micelles is 8‐ to 18‐fold smaller than that of monomer molecules. For permeability, the effective diffusion coefficient in the unstirred water layer adjacent to the epithelial membrane, and the free fraction at the epithelial membrane surface should be taken into account. The importance of these aspects is demonstrated here using several in vivo and clinical oral‐absorption data of low‐solubility model compounds. Using the theoretical equations, the food effect on oral absorption is further discussed.     

Substantivity of zinc salts used as rinsing solutions and their effect on the inhibition of Streptococcus mutans

The antimicrobial efficacy of zinc (Zn) salts (sulfate and acetate) against Streptococcus mutans (S. mutans) present in the oral cavity was tested in this study. The substantivity of Zn salts was assessed by determining the concentration of Zn in whole, unstimulated saliva and by measuring the magnitude of suppression of salivary S. mutans, 2h after rinsing. The concentration of Zn was measured by atomic absorption spectrometry (AAS) with electrothermal atomization (ET AAS) in saliva sampled before (basal) and 24h after mouth rinsing with different concentrations of Zn (0.1%, 0.5% and 1%) administrated as sulfate and acetate. The estimation of Zn levels in samples collected 30, 60, 90 and 120 min after rinsing was carried out by AAS with flame atomization (FAAS). Immediately after rinsing, the concentration of Zn in saliva sharply increased with respect to the baseline values (0.055+/-0.017 mg/L), followed by a sustained decrease, probably due to clearance of salivary flow or swallowing during sampling. A significant reduction (>87%) in the total mean S. mutans counts was found 2h after rinsing either with sulfate or acetate solutions, as evidence of the high substantivity and effectiveness of the Zn salts tested. A statistically significant inverse relationship (p<0.001 and the Pearson correlation coefficients between -34% and -50%) was found between Zn levels and the respective pH values measured in the samples collected 60 and 120 min after rinsing, sustaining the theory of bacterial glycolysis inhibition.     

Arginine utilization by Mycoplasma fermentans is not regulated by glucose metabolism: A 13C-NMR study

Abstract Electrofusion of protoplasts of two mutant strains of Hansenula polymorpha resulted in high fusion and hybrid yields when the calcium ions present in the conventional fusion medium replaced by zinc ions. The optimal fusion conditions were an alignment field of 0.4 kV cm⁻¹ strength and 2 MHz frequency for 30 s, followed by two consecutive pulses of 12 kV cm⁻¹ strength and 15 μs duration. With 0.05–0.1 mM zinc ions in the fusion medium an average clone number of 10⁴–10⁵ clones per 10⁸ input cells was reached. The presence of about 0.6 mM magnesium ions in the zinc fusion medium was essential.