Metabolism of some polyols by Rhizobium meliloti

The utilization of d-mannitol, d-arabitol, and d-sorbitol by Rhizobium meliloti was studied in extracts from mannitol-grown cells. Two different polyol dehydrogenases were induced by any of these polyols: (i) a nicotinamide adenine dinucleotide (NAD)-arabitol dehydrogenase and (ii) a NAD-sorbitol dehydrogenase, whereas polyol phosphate dehydrogenases were absent. d-Arabitol dehydrogenase was observed to act on both d-arabitol and d-mannitol, but d-sorbitol dehydrogenase acted specifically on d-sorbitol. d-Arabitol was oxidized to d-xylulose, d-mannitol and d-sorbitol were oxidized to d-fructose. An adenosine triphosphate-linked hexokinase which acts on d-fructose and absence of hexose isomerase were also detected in this organism.     

Induction of spherule formation in Physarum polycephalum by polyols

A method has been developed for inducing spherule formation (spherulation) in the myxomycete Physarum polycephalum by transferring the culture to synthetic medium containing 0.5 m mannitol or other polyols. This morphogenetic process occurred within 12 to 35 hr after the inducer was added. The mature spherules existed as distinct morphogenetic units, in contrast to the clusters of spherules formed during starvation. Ninety per cent of the spherules germinated by 24 hr in synthetic medium. The changes in the synthesis of ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and protein during plasmodial growth, spherulation, and germination of spherules are described. When spherule formation was completed, RNA, protein, and DNA decreased, compared with the values at the beginning of the conversion. The incorporation of (3)H-uridine into trichloroacetic acid-insoluble material was different in each of these periods, and this incorporation was sensitive to actinomycin D. The amount of glycogen increased during growth, whereas it decreased during spherulation. (14)C-glucose could be taken up by the cells in the presence of the inducer, and mannitol could not replace glucose as a source of energy. The mode of action of mannitol and its mechanism of induction are discussed.     

Inhibition of epsilon-poly-L-lysine biosynthesis in Streptomycetaceae bacteria by short-chain polyols

Antimicrobial epsilon-poly-L-lysine (ePL) is secreted by Streptomycetaceae bacteria, and the mechanism of ePL biosynthesis remains to be elucidated. We previously reported that an unknown ePL derivative accumulates in the culture medium of ePL-producing bacteria when glycerol is added to the culture medium (Nishikawa and Ogawa, Appl. Environ. Microbiol. 68:3575-3581, 2002). In this study, by using matrix-assisted laser desorption ionization-time of flight mass spectrometry and nuclear magnetic resonance, we identified the unknown derivative as the ester formed between the hydroxyl group of a glycerol molecule and the terminal carboxyl group of an ePL molecule. When a short-chain aliphatic polyol, such as ethylene glycol, propanediol, or butanediol, was added instead of glycerol, a corresponding ePL-polyol monoester accumulated in the culture medium of ePL-producing bacteria. ePL esterification was accompanied by ePL synthesis in intact cells and a cell-free system, but no esterification of exogenous ePL was observed. ePL-polyol esters were formed during lysine polymerization. The number of lysine residues of ePL-polyol esters decreased with increasing polyol concentration. Taken together, these results indicate that ePL synthesis is inhibited by polyols via esterification and that ePL elongation occurs via the incorporation of lysine monomers into the carboxyl terminus of ePL.     

Helix induction in antimicrobial peptides by alginate in biofilms

Bacterial exopolysaccharides provide protection against phagocytosis, opsonization, and dehydration and act as a major structural component of the extracellular matrix in biofilms. They contribute to biofilm-related resistance by acting as a diffusion barrier to positively charged antimicrobial agents including cationic antimicrobial peptides (CAPs). We previously created novel CAPs consisting of a nonamphipathic hydrophobic core flanked by Lys residues and containing a Trp residue in the hydrophobic segment as a fluorescent probe. Peptides of this type above a specific hydrophobicity threshold insert spontaneously into membranes and have antimicrobial activity against Gram-positive and Gram-negative bacteria at micromolar concentrations. Here we show that alginate, a polymer of beta-d-mannuronate and alpha-l-guluronate secreted by the cystic fibrosis pathogen Pseudomonas aeruginosa, induces an alpha-helical conformation detected by circular dichroism spectroscopy and blue shifts in Trp fluorescence maxima in peptides above the hydrophobicity threshold, changes typically observed upon association of such peptides with nonpolar (membrane) environments. Parallel effects were observed in the archetypical CAPs magainin II amide and cecropin P1. Fluorescence resonance energy transfer studies indicated that alginate induces peptide-peptide association only in peptides above the hydrophobicity threshold, suggesting that the hydrophilic alginate polymer behaves as an "auxiliary membrane" for the bacteria, demonstrating a unique protective role for biofilm matrices against CAPs.     

Biotechnological and in situ food production of polyols by lactic acid bacteria

Polyols such as mannitol, erythritol, sorbitol, and xylitol are naturally found in fruits and vegetables and are produced by certain bacteria, fungi, yeasts, and algae. These sugar alcohols are widely used in food and pharmaceutical industries and in medicine because of their interesting physicochemical properties. In the food industry, polyols are employed as natural sweeteners applicable in light and diabetic food products. In the last decade, biotechnological production of polyols by lactic acid bacteria (LAB) has been investigated as an alternative to their current industrial production. While heterofermentative LAB may naturally produce mannitol and erythritol under certain culture conditions, sorbitol and xylitol have been only synthesized through metabolic engineering processes. This review deals with the spontaneous formation of mannitol and erythritol in fermented foods and their biotechnological production by heterofermentative LAB and briefly presented the metabolic engineering processes applied for polyol formation.     

Production of polyols and ethanol by the osmophilic yeastZygosaccharomyces rouxii

Summary The yeastZygosaccharomyces rouxii ATCC 12572 was selected for its ability to produce appreciable levels of ethanol and of various polyols from concentrated glucose media (20 %, w/v).Z. rouxii was shown to yield large quantities of glycerol and of the mixture arabitol + mannitol. Good agitation combined with appropriate aeration (1 vvm) allowedZ. rouxii to utilize glucose readily leading to high polyol production. Depending on the fermentation conditions used,Z. rouxii ATCC 12572 will give either ethanol or various polyols as main fermentation product(s).     

Helix geometry in proteins

In this report we describe a general survey of all helices found in 57 of the known protein crystal structures, together with a detailed analysis of 48 alpha-helices found in 16 of the structures that are determined to high resolution. The survey of all helices reveals a total of 291 alpha-helices, 71 3(10)-helices and no examples of pi-helices. The conformations of the observed helices are significantly different from the "ideal" linear structures. The mean phi, psi angles for the alpha- and 3(10)-helices found in proteins are, respectively, (-62 degrees, -41 degrees) and (-71 degrees, -18 degrees). A computer program, HBEND, is used to characterize and to quantify the different types of helix distortion. alpha-Helices are classified as regular or irregular, linear, curved or kinked. Of the 48 alpha-helices analysed, only 15% are considered to be linear; 17% are kinked, and 58% are curved. The curvature of helices is caused by differences in the peptide hydrogen bonding on opposite faces of the helix, reflecting carbonyl-solvent/side-chain interactions for the exposed residues, and packing constraints for residues involved in the hydrophobic core. Kinked helices arise either as a result of included proline residues, or because of conflicting requirements for the optimal packing of the helix side-chains. In alpha-helices where there are kinks caused by proline residues, we show that the angle of kink is relatively constant (approximately 26 degrees), and that there is minimal disruption of the helix hydrogen bonding. The proline residues responsible for the kinks are highly conserved, suggesting that these distortions may be structurally/functionally important.     

Production of extracellular polyols in Aureobasidium pullulans

Aureobasidium pullulans produced extracellularly considerable amounts of polyols in the media with sucrose, glucose, fructose and mannose as sole carbon source during the late exponential and stationary phase of growth. The maximum yield of polyol was about 23% in the 20%(w/v) sucrose medium, of which mannitol was the main polyol associated with minute quantities of glycerol. Stress solutes such as NaCl and KCl did not promote polyol production.     

Structure and properties of polyurethanes prepared from triglyceride polyols by ozonolysis

Ozonolysis was used to obtain polyols with terminal primary hydroxyl groups and different functionalities from trilinolein (or triolein), low-saturation canola oil, and soybean oil. The functionality of the model polyol from triolein (trilinolein) was 3.0 and that of soy polyol was 2.5, due to the presence of unreactive saturated fatty acids, while canola gave a polyol with a functionality of 2.8. All polyols exhibited a high tendency to crystallize at room temperature. The resulting waxes had melting points comparable to that of paraffin and very low viscosities in the liquid state. The polyols were cross-linked using 4,4'-methylenebis(phenyl isocyanate) to give polyurethanes. Glass transitions (T(g)) for the model-, canola-, and soy-based polyurethanes were 53, 36, and 22 degrees C, respectively. The about 30 degrees C lower T(g) of the soy-based polyurethane than that of the model polyurethane was the result not only of lower functionality but also of the presence of saturated fatty acids in the former. Polyurethane from the canola polyol had intermediate cross-linking density and properties. These polyurethanes displayed excellent mechanical properties and higher glass transition temperatures compared to polyurethanes from epoxidized and hydroformylated polyols of the same functionality, presumably due to the absence or lower content of dangling chains in the former.     

Molecular mechanism underlying modulation of TRPV1 heat activation by polyols

Sensing noxiously high temperatures is crucial for living organisms to avoid heat-induced injury. The TRPV1 channel has long been known as a sensor for noxious heat. However, the mechanism of how this channel is activated by heat remains elusive. Here we found that a series of polyols including sucrose, sorbitol, and hyaluronan significantly elevate the heat activation threshold temperature of TRPV1. The modulatory effects of these polyols were only observed when they were perfused extracellularly. Interestingly, mutation of residues E601 and E649 in the outer pore region of TRPV1 largely abolished the effects of these polyols. We further observed that intraplantar injection of polyols into the hind paws of rats reduced their heat-induced pain response. Our observations not only suggest that the extracellular regions of TRPV1 are critical for the modulation of heat activation by polyols, but also indicate a potential role of polyols in reducing heat-induced pain sensation.     

Oxygen requirements for d-xylose fermentation to ethanol and polyols by Pachysolen tannophilus

The oxygen requirements for ethanol production from d-xylose (10 or 20 g l^?1) by Pachysolen tannophilus have been determined by controlling the availability of oxygen to shake flasks. Under anaerobic conditions no ethanol was produced whereas under aerobic conditions mainly biomass was formed. Semi-anaerobic conditions resulted in maximum ethanol production. By varying the stirring speed of a fermenter and supplying air to the liquid surface at various rates, the oxygen transfer rate (OTR) was controlled under semi-anaerobic conditions. By increasing the OTR from 0.05 to 16.04 mmol l^?1 h^?1, the ethanol yield coefficient decreased from 0.28 to 0.18 while the cell yield coefficient increased from 0.14 to 0.22. The accumulation of polyols decreased from 0.88 to 0.56 g l^?1 with increasing OTR. At OTRs between 0.09 and 1.18 mmol l^?1 h^?1, specific ethanol productivity attained a maximum value of 0.07 h^?1 and decreased with either increasing or decreasing OTR. The results indicate that the OTR must be carefully controlled for efficient ethanol production from d-xylose by P. tannophilus.     

Inhibition of cytochrome-P450 reductase by polyols has an electrostatic nature.

The present study was undertaken to examine the nature of the inhibitory action of glycerol on the liver microsomal monooxygenase system. In agreement with earlier observations, glycerol inhibited benzphetamine N-demethylation by liver microsomes of the phenobarbital-treated rabbit. The presence of glycerol in the medium did not affect binding of the substrate to cytochrome P450. Another polyol, ethylene glycol, was equally efficient in inhibiting benzphetamine N-demethylation. Both also inhibited reduction of rabbit cytochrome P450 LM2, cytochrome c and potassium ferricyanide by NADPH-cytochrome-P450 reductase in microsomes. Recently, we showed that the stimulation of electron transfer by increased ionic strength is due to neutralization of electrostatic interaction between NADPH-cytochrome-P450 reductase and its charged redox partners [Voznesensky, A. I. & Schenkman, J. B. (1992) J. Biol. Chem. 267, 14669-14676]. Polyols have an opposite effect to that of salt on ionic properties of a solution. They decrease the dielectric constant, thereby promoting electrostatic interactions between proteins. Addition of polyols decreased the conductivity of the medium. When rates of electron transfer to charged acceptors, cytochrome P450, cytochrome c and potassium ferricyanide, at various salt and polyol concentrations, relative to activities in 200 mM sodium phosphate, were plotted as a function of the conductivity the data for each acceptor fit on the same line. In contrast, neither alteration of ionic strength nor polyol addition affected the rate of electron transfer from NADPH-cytochrome-P450 reductase to an uncharged acceptor 1,4-benzoquinone. The data obtained is consistent with our earlier suggestion that charge repulsion limits redox interactions between rabbit cytochrome P450 LM2 and its reductase at low ionic strength, and suggest that the observed action of polyols is the result of enhancement of electrostatic interactions that inhibits electron transfer between NADPH-cytochrome-P450 reductase and its charged redox partners. In congruence with the hypothesis, the Km of rabbit cytochrome P450 LM2 for NADPH-cytochrome-P450 reductase was increased almost one order of magnitude by elevating the glycerol content from 5% to 25% (by vol.) without a change in Vmax.