Quantitative measurements on the acid taste and their bearing on the nature of the nerve receptor

Summary Quantitative determinations of the threshold concentrations for sourness of about 40 organic acids have been determined with an accuracy of about 6 per cent. Hydrogen ion concentrations have been obtained by use of the cell Hg/HgCl/KCl sat./organic acid/H₂. It is assumed that only undissociated acid molecules can cross the phase boundary between the aqueous solution and the nerve receptor, and that the stimulation of the sensation of sourness is due solely to hydrogen ion. All acids tasting equally sour should have the same pH within the nerve receptor. From the experimental data, relative concentration gradients for the nonionized acids have been calculated. It is shown that the addition of polar groups, such as OH, Cl, C=C, C=O, COOH, NH₂ to the organic acid make it from 20 to 500 times more difficult for the organic acid to penetrate into the nerve receptor. On the other hand, lengthening the carbon chain by addition of CH₂ groups makes penetration easier. The phenomena can be largely explained on the hypothesis that these organic acids are adsorbed into a tissue which is essentially like fat rather than like protein.     

Involvement of the glutamine synthetase/glutamate synthase pathway in ammonia assimilation by the wood-rotting fungusPleurotus ostreatus

The mycelium of the wood-rotting fungus,P. ostreatus, contains NAD-dependent glutamate synthase inhibited by azaserine.l-Glutamine andl-glutamate are the most important free amino acids in the mycelium. Feeding of the mycelium with nitrogenous substrates showed thatl-glutamate,l-aspartate andl-alanine are interconnected by way of transaminases. After the inhibition of glutamine synthetase by methionine-S-sulfoximine the synthesis ofl-glutamate was inhibited and the level of all free amino acids decreased. The¹⁵N-NMR spectra of mycelia after the addition of¹⁵NH₄Cl confirmed that the GS/GOGAT is the only pathway of ammonia assimilation inP. ostreatus and NAD-glutamate dehydrogenase should be the deaminating enzyme.     

The effects of reduced nitrogenous compounds suggests that glutamine synthetase activity is involved in the development of somatic embryos in carrot

The addition of l-glutamine, -alanine or l-glutamic acid strongly stimulates somatic embryo formation in carrot, not only in the number of somatic embryos formed but also with respect to their development. The effects of the amino acids on somatic embryogenesis were stronger than that of ammonium ion. In particular, l-glutamine strongly stimulated the development of somatic embryos. To clarify the different effects of amino acids and ammonium ion, the activity of glutamine synthetase (GS; EC 6.3.1.2), a key enzyme involved in nitrogen assimilation, was measured. Its activity decreased during the later stages of embryo development.Abbreviations -Ala -alanine - Glu l-glutamic acid - Gln l-glutamine - 2,4-D 2, 4-dichlorophenoxyacetic acid - -GHA l-glutamic acid -monohydroxamate - GS glutamine synthetase - MS medium Murashige & Skoog (1962) medium - MS-NH₄ medium MS medium without NH₄NO₃ - MS+NH₄ medium MS-NH₄ medium with 10 mM NH₄Cl - MS+ala medium MS-NH₄ medium with 10 mM -alanine - MS+GLU medium MS-NH₄ medium with 10 mM l-glutamic acid - MS+GLN medium MS-NH₄ medium with 10 mM l-glutamine - NIR nitrite reductase - NR nitrate reductase     

Taste responses of the gerbil IXth nerve

Summated taste responses to 12 taste solutions were recordedfrom the IXth (glossopharyngeal) nerve of 38 Mongolian gerbils(Meriones unguiculatus). 0.3 M NH₄Cl was the most effectivestimulant. The relative magnitude of the peak summated responsewas a positively accelerated function of log molar concentration.Absolute thresholds were determined for three chemicals: 0.002M NaCl, 0.0003 M HCl, and 0.002 M sucrose. The relative magnitudesof the responses to quinine, NH₄Cl, and KCl were greater forthe IXth nerve than for the chorda tympani nerve, whereas NaClwas more effective for the chorda tympani. A similar patternis seen in the rat. Acetic and citric acid may bind to commonreceptor sites. NH₄Cl, KCl, and HCl may also have receptor sitesin common.     

Taste attractiveness of free amino acids and their physicochemical and biological properties (as exemplified by fishes)

Using fishes (32 species, 11 families) as an example, the relationship between the taste attractiveness of free amino acids (L-isomers) and their physicochemical and biological properties was analyzed. It was shown that essential amino acids, most nutritionally required for an organism, have lower taste attractiveness for fishes than nonessential amino acids. Only in 6 of the 32 tested species (sunbleak Leucaspius delineatus, European minnow Phoxinus phoxinus, dace Leuciscus leuciscus, chub Leuciscus cephalus, blue gourami Trichopodus trichopterus, pearl gourami Trichopodus leerii) the relationship between the taste attractiveness and molecular weight of amino acids was supported statistically, being negative in all cases. Only in 2 species, a statistically significant correlation between the taste properties of amino acids and the dissociation constant (K₁) was found, positive in the stone loach Barbatula barbatula and negative in the lake char Salvelinus namaycush. A positive correlation between taste preferences and the magnitude of the isoelectric point (pI) of amino acids was found in one species (roach Rutilus rutilus) and a negative correlation in 2 species (brown trout Salmo trutta and Arctic char Salvelinus alpinus erythrinus). A statistically significant correlation between the taste attractiveness and water solubility of amino acids was revealed in 2 species (chum salmon Oncorhynchus keta and navaga Eleginus nawaga), negative in both cases. The flavor, which stimulates food intake, was found to be more often intrinsic to acidic and polar uncharged than basic and nonpolar amino acids, L- than D-isomers, amino acids with an amino group at the α- than β-position. Amino acids are more attractive than their salts. Aromatic amino acids are much less attractive than S-containing or acyclic amino acids. Thus, in most fish species there is no or weak relationship between the taste attractiveness of free amino acids and many of their physical, chemical and biological properties, suggesting a mediated character of this relationship and/or its poor detectability.     

The production of labeled betaine by incubation of osmolyte-freePseudomonas aeruginosa with radioactive choline

A simple, efficient, and economical method is presented for the preparation of radioactive betaine. It involves the incubation of radioactive choline with osmolyte-freePseudomonas aeruginosa previously grown in hyperosmolar medium with choline as an osmoprotectant. The summarized procedure was as follows: (i) bacteria were grown in high P_i basal salt medium (HP_i-BSM) with 20mm succinate, 18.7mm NH₄Cl, 0.8m NaCl, and 1mm nonradioactive choline. After the bacterial pellet was obtained, it was suspended in deionized water to release osmolytes accumulated during growth; (ii) suspension of the pellet, free of osmolytes, in hyperosmolar HP_i-BSM with [methyl-¹⁴C]-choline (55 nCi/nmol) without the carbon and nitrogen sources. Incubation of the mixture at 37°C for 8–30 h. When only 10% of the initial radioactivity remained in the supernatant, it was withdrawn after centrifugation and the pellet suspended in deionized water. This step released the accumulated betaine plus some contaminants. Purification of betaine contained in the aqueous supernatant was carried out after rotoevaporation to dryness and solubilization of the residue in methanol. The methanolic extract was rotoevaporated to dryness, the residue solubilized in 10% acetic acid and transferred to a Dowex 50-X8 column. After the column was washed with water and 2m NH₄OH, betaine was eluted by the addition of 4m NH₄OH. The total procedure for obtaining pure radioactive betaine resulted in a yield of 80%. The product obtained was chemically and radiochemically pure, with a specific radioactivity of 54±1 nCi/nmol.     

Cations and Anions as Modifiers of Ryanodine Binding to the Skeletal Muscle Calcium Release Channel

Rate and equilibrium measurements of ryanodine binding to terminal cysternae fractions of heavy sarcoplasmic reticulum vesicles demonstrate that its activation by high concentrations of monovalent salts is based on neither elevated osmolarity nor ionic strength. The effect of the ions specifically depends on their chemical nature following the Hofmeister ion series for cations (Li⁺ < NH⁺ ₄ < K⁻∼ Cs⁺≤ Na⁺) and anions (gluconate⁻ < Cl⁻ < NO₃ ⁻∼ ClO₄ ⁻∼ SCN⁻) respectively, indicating that both are involved in the formation of the salt-protein complex that can react with ryanodine. Activation by rising salt concentrations exhibits saturation kinetics with different dissociation constants (25–11 m) and different degrees of cooperativity (n= 1.5–4.0) for the respective salts. Maximal second order binding rates between 40,000 and 80,000 (m ⁻¹· sec⁻¹) were obtained for chlorides and nitrates of 1a group alkali ions with the exception of lithium supporting only rates of maximally 10,000 (M⁻¹· sec⁻¹). The nitrogen bases, NH⁺ ₄ and Tris⁺, in combination with chloride or nitrate, behave divergently. High maximal binding rates were achieved only with NH₄NO₃. The dissociation constants for the ryanodine–protein complexes obtained by measurements at equilibrium proved to depend differently on salt concentration, yet, converging to 1–3 nm for the applied salts at saturating concentrations. The salts do not affect dissociation of the ryanodine protein complex proving that the effect of salts on the protein's affinity for ryanodine is determined by their effect on the on-rate of ryanodine binding. ATP and its analogues modify salt action resulting in elevated maximal binding rates and reduction or abolition of binding cooperativity. Linear relations have been obtained by comparing the rates of ryanodine binding at different salt concentrations with the rates or the initial amplitudes (15 sec) of salt induced calcium release from actively loaded heavy vesicles indicating that the various salts promote specifically and concentration dependently channel opening and its reaction with ryanodine. Received: 9 February 1998/Revised: 24 April 1998     

Conversion of phenylpyruvate to l-phenylalanine by immobilized Clostridium butyricum-alanine dehydrogenase-Micrococcus luteus under hydrogen high pressure

Summary Alanine was the best amino donor among various amino acids and NH₄Cl for the phenylalanine production of Micrococus luteus. l-Alanine was regenerated at the rate of 9.2 moles/min/g dry cells from NH₄Cl and pyruvate by immobilized Clostridium butyricum-alanine dehydrogenase. l-Phenylalanine was continuously produced from hydrogen, NH₄Cl and phenylpyruvate by coupling immobilized C. butyricum, alanine dehydrogenase and M. luteus. The rate of phenylalanine production was 1.74 moles/min/g dry cells.     

New culture media to suppress exopolysaccharide production by Rhizobium japonicum

Summary Secretion of exopolysaccharide by Rhizobium japonicum strain USDA 110 ws measured during growth on media comprising 12.5 mM MES [2-(N-morpholino)ethanesulfonic acid] buffer, pH 5.9; 5 mM NH₄Cl; trace elements; and 25 or 100 mM of one of 23 different carbon sources. Significant amounts of exopolysaccharide were produced on all aldopentoses, polyols, organic acids, and sugar acids tested, but little or none was secreted during growth on aldohexoses or amino acids. Media suitable for routine slime-free culture of several. R. japonicum strains were made by using 100 mM d-galactose or 25 mM l-aspartate as the carbon source.     

The Permeation of Ammonium through a Voltage-independent K+ Channel in the Plasma Membrane of Rye Roots

Nitrogen is available to the plant in the form of NH⁺ ₄ in the soil solution. Here it is shown that a voltage-independent K⁺ channel in the plasma membrane of rye (Secale cereale L.) roots is permeable to NH⁺ ₄. The channel was studied following its incorporation into planar 1-palmitoyl-2-oleoyl phosphatidyl ethanolamine bilayers. The unitary conductance of the channel was greater when assayed in the presence of 100 mm NH₄Cl than 100 mm KCl. However, the probability of finding the channel open (P _o ) was lower in the presence of 100 mm NH₄Cl (P _o = 0.63) than in 100 mm KCl (P _o = 0.8), suggesting that P _o can be regulated by the (permeant) ions present in solution. When assayed in equimolar concentrations of NH₄Cl (cis) and KCl (trans), the zero-current (reversal) potential for the channel (E _rev) exhibited a complex concentration dependence. At low cation concentrations, the apparent permeability of NH⁺ ₄ relative to K⁺ (P_NH4/P_K) was greater than 1.0. However, as the cation concentration was increased, P_NH4/P_K initially decreased to a minimum of 0.95 at 3 mm before increasing again to a maximum of 1.89 at 300 mm. At cation concentrations above 300 mm, P_NH4/P_K decreased slightly. This implies that the pore of the channel can be occupied by more than one cation simultaneously. Ammonium permeation through the pore was simulated using a model which is composed of three energy barriers and two energy wells (the ion-binding sites). The model (3B2S) allowed for single-file permeation, double cation occupancy, ion-ion repulsion within the pore and surface potential effects. Results indicated that energy peaks and energy wells were situated asymmetrically within the electrical distance of the pore, that cations repel each other within the pore and that the vestibules to the pore contain negligible surface charge. The energy profile obtained for NH⁺ ₄ is compared with ones obtained for K⁺ and Na⁺. This information allows the fluxes through the K⁺ channel of the three major monovalent cations present in the soil solution to be predicted. Received: 16 October 1995/Revised 12 March 1996     

Pentavalent Vanadium at Concentration of the Underground Water Level Enhances the Sweet Taste Sense to Glucose in College Students

Underground water in volcanic areas contains vanadium when the basalt layer exists among igneous rocks. The concentration of vanadium in drinking water sometimes exceeds 0.8 μM in these areas, however, the physiological effects of vanadium, especially non-toxic effects, at concentrations lower than 1 μM are unknown. In the present experiments, we examined the effect of pentavalent vanadium and tetravalent vanadium at 0.8 and 8.0 μM concentrations on the recognition threshold to taste substances in healthy college students. Pentavalent vanadium, ammonium vanadate, lowered the sweet taste threshold to glucose at 0.8 and 8.0 μM as well. Tetravalent vanadium, vanadium sulfate, did not alter the threshold to glucose either at 8.0 μM or at 0.8 μM. Ammonium vanadate also decreased the sweet taste threshold to l-proline at 8.0 μM. Ammonium vanadate did not influence the sour taste threshold to hydrogen chloride. Neither ammonium sulfate nor ammonium bicarbonate altered the sweet taste threshold to glucose. Therefore, the effect of ammonium vanadate on the sweet taste threshold is attained by vanadium but not by ammonium. It was concluded that pentavalent vanadium at 0.8 μM intensifies the sweet taste sense to glucose rather specifically. We have first shown the physiological effect of vanadium at the concentration of the underground water level.     

The effects of a cyclic polyether on the electrical properties of phospholipid bilayer membranes

Summary The cyclic polyether XXXII, a neutral, lipid soluble molecule, produces large increases in the conductance of bilayer membranes formed from a variety of lipids. The conductance increases linearly with the concentration of alkali metal cation but with the square, and at higher concentrations the cube, of the polyether concentration. This implies that two or three polyether molecules combine with a single cation to carry it across the membrane. In the presence of XXXII the bilayer is permeable solely to cations and the membrane potential is described by an equation of the Goldman-Hodgkin-Katz type. The permeability ratios determined from potential measurements are independent of salt concentration, decrease in the sequence Cs>Rb>K>NH₄>Na>Li(1.0,0.25, 0.15, 0.075, 0.007, 0.0013) and are equal to the conductance ratios at low (e.g. 10^–3 m) salt concentration. At higher salt concentrations, the permeability and conductance ratios are not equal and maxima in the conductancevs. salt concentration curves are observed. Both these phenomena are postulated to be caused by the formation of relatively impermeant 11 polyether cation complexes in the aqueous phase. The 11 aqueous association constants deduced from bilayer measurements decrease in the sequence K>Rb>Na>NH₄>Cs>Li (120, 34, 26, 19, 12, 4 liters per mole) and agree quantitatively with the literature values for the more water soluble polyether XXXI, which lacks only thet-butyl groups of XXXII.     

Evidence for Negative Charge in the Conduction Pathway of the Cardiac Ryanodine Receptor Channel Provided by the Interaction of K+ Channel N-type Inactivation Peptides

We have investigated the interaction of two peptides (ShB — net charge +3 and ShB:E12KD13K — net charge +7) derived from the NH₂-terminal domain of the Shaker K⁺ channel with purified, ryanodine-modified, cardiac Ca²⁺-release channels (RyR). Both peptides produced well resolved blocking events from the cytosolic face of the channel. At a holding potential of +60 mV the relationship between the probability of block and peptide concentration was described by a single-site binding scheme with 50% saturation occurring at 5.92 ± 1.06 μm for ShB and 0.59 ± 0.14 nm for ShB:E12KD13K. The association rates of both peptides varied with concentration (4.0 ± 0.4 sec⁻¹μm ⁻¹ for ShB and 2000 ± 200 sec⁻¹μm ⁻¹ for ShB:E12KD13K); dissociation rates were independent of concentration. The interaction of both peptides was influenced by applied potential with the bulk of the voltage-dependence residing in K_off. The effectiveness of the inactivation peptides as blockers of RyR is enhanced by an increase in net positive charge. As is the case with inactivation and block of K⁺ channels, this is mediated by a large increase in K_on. These observations are consistent with the proposal that the conduction pathway of RyR contains negatively charged sites which will contribute to the ion handling properties of this channel. Received: 15 December 1997/Revised: 13 March 1998     

Extracellular and intracellular chemical environments in relation to embryogenesisin vitro

Summary Tissue culture isolated from the root ofDaucus carota readily produced embryos when they were grown on a medium (M_s) containing relatively large amounts of NH₄ ⁺ and nitrate. Embryos were never formed on a second medium (M_w) which contained only nitrate in a low concentration. The cells of M_s-cultures always had a high level of NH₄ ⁺ while it was scarcely detected in M_w-cultures. Addition of either nitrate or glutamate to M_w resulted in the formation of embryos and also in the accumulation of a detectable amount of NH₄ ⁺ in the cells of the tissues. Although the occurrence of NH₄ ⁺ in the medium is not necessary for embryo formationin vitro it appears that a certain level of intracellular NH₄ ⁺ is a prerequisite for this process. Since there is a positive correlation between embryo formation and the contents in the cultures of both soluble and insoluble organic nitrogen, it is probable that NH₄ ⁺ is important for embryo formation because it is an essential substrate for the synthesis of organic nitrogen compounds such as amino acids and proteins. The ability to synthesize organic nitrogen from NH₄ ⁺ decreased conspicuously in the tissues which were cultured on M_s for long periods of time and had lost the capacity to form embryos. A certain level of K⁺ in culture media is necessary for optimal production of embryos on media with NH₄ ⁺, while Na⁺ has no effect on embryo formation.The authors are indebted to Mr. E.Mahn, Miss S.Semenoff, and Mrs. E.Bock for their technical assistances.     

Altered Kinetic Properties of Tyrosine-183 to Cysteine Mutation in Glutamine Synthetase of <Emphasis Type="Italic">Anabaena variabilis</Emphasis> Strain SA1 Is Responsible for Excretion of Ammonium Ion Produced by Nitrogenase

A L-methionine-D,L-sulfoximine-resistant mutant of the cyanobacterium Anabaena variabilis, strain SA1, excreted the ammonium ion generated from N₂ reduction. In order to determine the biochemical basis for the NH₄ ⁺-excretion phenotype, glutamine synthetase (GS) was purified from both the parent strain SA0 and from the mutant. GS from strain SA0 (SA0-GS) had a pH optimum of 7.5, while the pH optimum for GS from strain SA1 (SA1-GS) was 6.8. SA1-GS required Mn⁺² for optimum activity, while SA0-GS was Mg⁺² dependent. SA0-GS had the following apparent K _m values at pH 7.5: glutamate, 1.7 mM; NH₄ ⁺, 0.015 mM; ATP, 0.13 mM. The apparent K _m for substrates was significantly higher for SA1-GS at its optimum pH (glutamate, 9.2 mM; NH₄ ⁺, 12.4 mM; ATP, 0.17 mM). The amino acids alanine, aspartate, cystine, glycine, and serine inhibited SA1-GS less severely than the SA0-GS. The nucleotide sequences of glnA (encoding glutamine synthetase) from strains SA0 and SA1 were identical except for a single nucleotide substitution that resulted in a Y183C mutation in SA1-GS. The kinetic properties of SA1-GS isolated from E. coli or Klebsiella oxytoca glnA mutants carrying the A. variabilis SA1 glnA gene were also similar to SA1-GS isolated from A. variabilis strain SA1. These results show that the NH₄ ⁺-excretion phenotype of A. variabilis strain SA1 is a direct consequence of structural changes in SA1-GS induced by the Y183C mutation, which elevated the K _m values for NH₄ ⁺ and glutamate, and thus limited the assimilation of NH₄ ⁺ generated by N₂ reduction. These properties and the altered divalent cation-mediated stability of A. variabilis SA1-GS demonstrate the importance of Y183 for NH₄ ⁺ binding and metal ion coordination. Received: 3 July 2002 / Accepted: 29 July 2002     

Occurrence and Bacterial Cycling of d Amino Acid Isomers in an Estuarine Environment

Abundance of d isomers of amino acids has been used in studies of organic matter diagenesis to determine the contribution of bacterial biomass to the organic matter, especially in marine sediments. However, fluxes of d amino acids in pelagic waters are poorly known. Here we present seasonal changes (March–September) in concentrations of dominant d amino acids in the pool of dissolved free and combined (hydrolysable) amino acids (DFAA and DCAA) in the shallow Roskilde Fjord, Denmark. The amino acid dynamics are related to pelagic bacterial density and activity and abundance of viruses. d␣isomers made up 3.6 and 7.9% of the DFAA and DCAA (average values), respectively, and had similar seasonal variations in concentrations. In batch cultures (0.7- and 0.2-m filtered water in a 1:9 mixture) microbial activity reduced l+d DCAA concentrations in seven of ten sampling dates, while DCAA were released at the remaining three sampling times. NH₄⁺ balance (uptake or release) in the cultures correlated significantly with variations in concentrations of d-DCAA, but not with the total DCAA pools. Abundance of viruses did not correlate with density or production of bacteria in the fjord, but covaried with mineralization of total C, DCAA and PO₄³⁻ in the batch cultures. The content of d amino acids in bacterial biomass in the cultures varied from 6.7 to 12.5% and correlated with the d isomer concentration in the fjord, except for d-Ala. In an additional six-day batch culture study, DCAA and d-DCAA were assimilated by the bacteria during the initial 36 h, but were released between 36 and 42 h simultaneous with a decline in the bacterial density. Our results demonstrate that peptidoglycan components contribute to natural amino acid pools and are assimilated by bacterial assemblages. This cell wall “cannibalism” ensures an efficient recycling of nutrients within the microbial community. Significant positive correlations between viral abundance and bacterial mineralization of organic matter in the fjord indicated that viral lysis contributed to this nutrient recycling.     

Variable cellular composition of Chromatium in growing cultures

Summary A strictly anaerobic spirochete was isolated from a sample of marine mud. The organism possessed two axial fibrils entwined with the regularly coiled protoplasmic cylinder. An outer envelope or sheath enclosed both protoplasmic cylinder and axial fibrils. The spirochete grew in chemically defined media containing glucose, amino acids or NH₄Cl, sulfide, NaCl, vitamins, coenzyme A, and in-organic salts. A reducing agent, such as sodium sulfide or l-cysteine, as well as exogenous supplements of biotin, niacin and coenzyme A were required for growth. Pantothenate replaced coenzyme A as an exogenous growth factor, but the resulting cell yields were low. The spirochete grew in media prepared with sea water, but not in fresh water media containing less than 0.05 M NaCl (optimum concentration 0.35 M). Both Na⁺ and Cl^- were required. Carbohydrates served as fermentable substrates. Amino acids, sugar alcohols, tricarboxylic acid cycle intermediates, and other organic acids and alcohols were not fermented. Glucose was fermented to ethyl alcohol, acetate, CO₂, H₂, and small amounts of lactate, formate and pyruvate. The guanine + cytosine content of the DNA of the spirochete was 50.5 moles-% (buoyant density). It is proposed that the marine isolate be considered a new species and that it be named Spirochaeta litoralis.     

Comparison of the biological activity of fusicoccin in higher plants with its binding to plasma membranes

The concentration dependences of the binding of fusicoccins (FCs) A, B, C, D, J and H to plasma membranes isolated from maize (Zea mays L.) roots have been studied in parallel with the effects of these compounds on elongation and ⁸⁶Rb transport in detached maize roots. The dissociation constants obtained showed a good correlation between the affinity of the FCs for the plasmalemma and their biological activity. However, the range of physiologically active FC concentrations proved to be about two orders of magnitude higher than that calculated from the dissociation constants. It was also shown that Vicia faba L. mesophyll protoplasts, unlike isolated plasma membranes, have two FC-binding sites, one with a K _D similar to that of the isolated plasmalemma while the other has a substantially higher K _D , apparently corresponding to the physiologically active state of the FC-binding proteins.Abbreviation FC fusicoccin     

Dissociation of Human αB-Crystallin Aggregates by Thiocyanate Is Structurally and Functionally Reversible

Conformational modifications and changes in the aggregation state of human αB-crystallin were investigated at different concentrations of SDS, KBr, urea, and NH₄SCN and at different temperatures. Intrinsic fluorescence measurements indicated complete and reversible unfolding of the protein at 2 M NH₄SCN, whereas the concentration of urea required for complete and irreversible unfolding was 6 M. Gel permeation chromatography indicated almost complete dissociation of the micelle-like aggregate of αB-crystallin in 2 M NH₄SCN, but only partial dissociation into large-sized aggregates in 6 M urea. Thiocyanate-treated αB-crystallin recovered its chaperone-like activity upon dilution of the dissociating agent, whereas the urea-treated protein did not.     

Decoloration of azo dyes by three whiterot fungi: influence of carbon source

Two strains of Phanerochaete chrysosporium and a local isolate of white-rot fungus, if pre-cultured in a high nitrogen medium with glucose, could decolorize two azo dyes (Amaranth and Orange G) and a heterocyclic dye (Azure B). When starch was used in the pre-cultivation medium, decoloration of Orange G occurred if the medium also contained 12mM NH₄Cl, whether or not veratric acid was present. In medium containing 1.2mM NH₄Cl and veratric acid, greater decoloration occurred with one strain of P. chrysosporium and the local isolate. In preculture medium with cellulose and 1.2mM NH₄Cl, decoloration by the local isolate was enhanced but not that by the other strains.The authors are with the Department of Microbiology, Soochow University, Shih Lin, Taipei, Taiwan