Henry Schneider

Screening of yeasts for production of xylitol fromd-xylose and some factors which affect xylitol yield inCandida guilliermondii

SummaryThe ability to convertd-xylose to xylitol was screened in 44 yeasts from five genera. All but two of the strains produced some xylitol with varying rates and yields. The best xylitol producers were localized largely in the speciesCandida guilliermondii andC. tropicalis. Factors affecting xylitol production by a selectedC. guilliermondii strain, FTI-20037, were investigated. The results showed that xylitol yield by this strain was affected by the nitrogen source. Yield was highest at 30–35°C, and could be increased with decreasing aeration rate. Using high cell density and a defined medium under aerobic conditions, xylitol yield byC. guilliermondii FTI-20037 from 104 g/ld-xylose was found to be 77.2 g/l. This represented a yield of 81% of the theoretical value, which was computed to be 0.9 mol xylitol per mold-xylose.

A spin probe study of the influence of cholesterol on motion and orientation of phospholipids in oriented multibilayers and vesicles.

Abstract Spin probes have been used to study at the molecular level the influence of cholesterol on bilayers of egg lecithin and dipalmitoyl lecithin. Distinct differences between the two lecithin systems were revealed. Increasing amounts of cholesterol result in extension of the fatty acid chains and decreased amplitude of motion of the long axes of the fatty acids in egg lecithin. In dipalmitoyl lecithin cholesterol causes an increase in the mobility and amplitude of motion of the fatty acid side chains, presumably due to alteration of the molecular interactions between phospholipids by relaxing the close packing of these molecules. These data provide an explanation for the condensing and fluidizing effects of cholesterol in water-containing phases and monolayers of egg lecithin and dipalmitoyl lecithin, respectively, and for the permeability behavior of egg lecithin and dipalmitoyl lecithin liposomes in the presence and absence of cholesterol. Differences are revealed between the spin bilayer environments in hydrated phospholipid films and vesicles.

Acetyl xylan esterases in fungal cellulolytic systems

Xylan of several tree and other plant species is acetylated, and the enzymology of its degradation is unknown. The present study shows that enzymes liberating acetic acid from an acetylated xylan occur in several fungal cellulolytic systems. Consequently, an additional step will have to be considered in current concepts for the degradation of hemicellulose by xylanases and xylosidases.

The effects of alcohols on lipid bilayers: A spin label study☆

Aliphatic alcohos produce changes in the structural arrangement of lipids in bilayers as indicated by studies using the steroid spin probe 3-spiro-2′-(N-oxyl-4′,4′-dimethyloxazolidine)) cholestane. The concentrations of alcohol corresponding to the onset of perceptible changes in organization correlate well with those causing anesthesia in biological systems, suggesting that anesthesia may be caused by small disruptions of lipid bilayer structure in biological membranes. The data indicate also that lipid bilayer disruption or reorganization is involved in alcohol effects on black lipid membrane conductivity and erythrocyte antihemolysis.

Sterol structure and ordering effects in spin-labelled phospholipid multibilayer structures.

Abstract : Cholesterol is a common component of vertebrate cellular membranes. Sterols with a similar structure (3beta-OH group, hydrocarbon chain at position 17) are also found in vascular plants, algae, fungi, and microorganisms. The biological function of these compounds is not completely understood. The authors investigated the effects of steroid structure on the degree of order in multibilayer structures of polar membrane lipids using a spin label technique. The results indicate that cholesterol and structurally related sterols increase the degree of order of the spin label, and hence that of the lipids in the lamellar structure. (Author)

Interaction of cultured mammalian cells with WR-2721 and its thiol, WR-1065: implications for mechanisms of radioprotection.

An isothermal microcalorimeter was used to measure changes in heat flow when radioprotective drugs were added to cultured mammalian cells. The heat produced when WR-2721 was added continued for at least 90 min. WR-2721 was dephosphorylated by the cells to thiol (WR-1065) which oxidizes to disulphide. In the microcalorimeter, thiols give an immediate burst of heat due to this oxidation. A biological oxygen monitor revealed that WR-1065 and cysteamine rapidly consumed all the oxygen in culture medium. (10 mM WR-1065 deoxygenated medium in 2 min.) Rapid consumption of oxygen by radioprotective thiols indicates that they will not co-exist with oxygen for long in cells. This has two important implications with respect to mechanisms of radioprotection: (1) oxygen in tissues will be consumed rapidly and could result in local hypoxia; and, (2) at modest doses of protective agents the thiol will be consumed in oxic cells and hence very little will be available for reactions such as hydrogen donation. Our results indicate that anoxia is probably the principal mechanism of protection by aminothiols in mammals and aerated cells. This has major implications for clinical applications of radioprotectors and these are discussed.

The membrane concentrations of alcohol anesthetics

Abstract 1. 1. This work provides evidence for the Overton-Meyer partition theory of anesthesia. This theory states that the cell membrane anesthetizing concentration is of the order of 0.03 molal (moles of anesthetic per kg membrane). The membrane concentrations found experimentally for alcohols ranged from 0.01 molal for decanol to 0.04 Molal for pentanol in hemoglobin-free erythocyte ghost membranes at concentrations which are 25% effective in protecting erythrocyte membranes, and which are also effective in stabilizing nerve fibers. Since the membrane concentration decreased linearly with chain length by a factor of about one-third on going from pentanol to decanol, the pharmacological intrinsic efficacy of decanol (in the membrane phase) is 3.2 times greater than that of pentanol. 2. 2. The decrease in membrane concentration ( c membrane ) with increasing chain length of the alcohols indicated that some size-dependent parameter of the anesthetic was important in determining the final amount of membrane stabilization. Mullins 19 had predicted that such a parameter should exist and suggested that it is the volume of the anesthetic molecule, V mol . The data support this insofar as V mol ·c membrane is almost the same for all the alkanols. The data also support, however, a new hypothesis which states that the membrane concentration should be corrected by δF , the free energy of binding, since this parameter is possibly the most general index of the “extensive” influence of the anesthetic in the drug-receptor interaction. The value for ΔF·c membrane was of the order of 60 cal/kg membrane for each alkanol. 3. 3. The mean free energy of alcohol adsorption was −695 ± 81 (S.E.) cal/mole of methylene groups, indicating that the membrane-alcohol interaction was hydrophobic. 4. 4. Assuming an unlimited number of membrane binding sites, the membrane/buffer partition coefficients could be averaged; the mean values were 3·4 for pentanol, 39 for heptanol, 152 for octanol, 582 for nonanol, and 1226 for decanol. Assuming there was only a finite number of binding sites, the mean for the maximum number of alcohol binding sites was computed to be 65.5 mmoles of alkanol per kg of dry membrane.

Fermentation of a pentose by yeasts

Summary Several yeasts have been found to be able to ferment D-xylulose, a catabolite of D-xylose, and to produce ethanol thereby. The fermentation is carried out by several species which can utilise D-xylose oxidatively as well as by several which cannot do so. Xylose itself, and the other aldopentoses, are not utilised anaerobically by yeasts. Fermentation of D-xylulose by D-xylose oxidising species indicates that a control operates under conditions of low oxygen tension which prevents the catabolism of D-xylose to D-xylulose. The results are pertinent in efforts to obtain yeasts which can ferment biomass pentoses, a problem of interest in attempts to obtain a liquid fuel from a renewable resource.

Xylan-hydrolysing enzymes from Streptomyces spp.

Screening of some mesophilic species of Streptomyces indicated that enzyme activities capable of removing O-acetyl, arabinosyl, 4-O-methylglucuronyl, and feruloyl substituents from xylan were present in culture filtrates, in addition to endo-β-(1,4)-xylanases. Low constitutive levels of acetyl xylan esterase, arabinosidase, 4-O-methylglucuronidase, and ferulic acid esterase could be greatly elevated by supplementation of liquid media with starch-free wheat bran, oat spelts xylan, or sugar cane bagasse. One organism, S. olivochromogenes, produced particularly high levels of acetyl xylan esterase, ferulic acid esterase, arabinosidase, and 4-O-methylglucuronidase as well as endo-β-(1,4)-xylanase. Partial purification of extracellular preparations from S. flavogriseus and S. olivochromogenes disclosed the presence of multiple forms of both anionic and cationic enzyme activities. Several of the hydrolysing activities occurred as “families” in association with endo-β-(1,4)-xylanase.

Conversion of Pentoses to Ethanol by Yeasts and Fungi

Fermentation of D-xylose is of interest in enhancing the yield of ethanol obtainable from lignocellulosic hydrolysates. Such hydrolysates can contain both pentoses and hexoses, and while technology to convert hexoses to ethanol is well established, the fermentation of pentoses had been problematical. To overcome the difficulty, yeasts and fungi have been sought and identified in recent years that can convert D-xylose into ethanol. However, operation of their cultures in the presence of the pentose to obtain rapid and efficient ethanol production is somewhat more complex than in the archetype alcoholic fermentation, Saccharomyces cerevisiae on D-glucose. The complexity stems, in part, from the association of ethanol accumulation in cultures where D-xylose is the sole carbon source with conditions that limit growth, by oxygen in particular, although limitation by other nutrients might also be implicated. Aspects of screening for appropriate organisms and of the parameters that play a role in determining culture variables, especially those associated with ethanol productivity, are reviewed. Performance with D-xylose as sole carbon source, in sugar mixtures, and in lignocellulosic hydrolysates is discussed. A model that involves biochemical considerations of D-xylose metabolism is presented that rationalizes the effects of oxygen on cultures where D-xylose is the sole carbon source, notably effects of the specific rate of oxygen use on the rate and extent of ethanol accumulation. Alternate methods to direct fermentation of D-xylose have been developed that depend on its prior isomerization to D-xylose, followed by fermentation of the pentulose by certain yeasts and fungi. Factors involved in the biochemistry, use, and performance of these methods, which with some organisms involves sensitivity to oxygen, are reviewed.