PTC and PROP behave differently in tests of discrimination from their solvents

Better discrimination was possible between phenylthiocarbamide (PTC) solutions and the pure solvent when the solvent was a tasteless low- concentration NaCl solution to which the subject had adapted than when the solvent was purified water. The reverse was true for 6-n- propylthiouracil (PROP). The differences in discrimination for PROP and PTC in the different solvents were caused by differences in the intensity and persistence of aftertastes, rather than a more intense perception of the PTC and PROP tastes per se. This has consequences for traditional approaches to measuring taste sensitivity, as well as indicating that PTC and PROP are not necessarily equivalent indicators of 'taster' versus 'non-taster' status.      

Proton transfer in methylmalonyl-CoA epimerase from Propionibacterium shermanii. The reaction of (2R)-methylmalonyl-CoA in tritiated water.

The reaction catalysed by methylmalonyl-CoA epimerase from Propionibacterium shermanii was studied in tritiated water, in the direction with (2R)-methylmalonyl-CoA as substrate, under 'irreversible' conditions. After partial reaction, even when most of the substrate had been converted into product (isolated as propionyl-CoA) essentially no solvent tritium appeared in residual (2R)-methylmalonyl-CoA. The product, however, did contain tritium, and the specific radioactivity of the (2S)-epimer was deduced to be 0.33 times that of the solvent. These results provide further support for the mechanism proposed for the epimerase-catalysed reaction in the accompanying paper [Leadlay & Fuller (1983) Biochem. J. 213, 635-642], in which two enzyme bases act respectively as proton donor and acceptor. The observed low discrimination against solvent tritium entering the product can be accounted for by a mechanism in which the release of product is slow, and the re-protonation step on the enzyme is reversible, without leading to isotopic exchange with the solvent.     

Use of non-conventional media inMorinda citrifolia cell cultures

Non-conventional media, containing organic solvents as supplement, were exploited to obtain the non-lethal product release of plant cell secondary metabolites, using suspension cultures ofMorinda citrifolia as model system. The results of our preliminary studies about solvent biocompatibility show that the discrimination between biocompatible and toxic solvents can be achieved by means of two parameters: log P and critical solvent concentration. The last one seems to be a better indicator of solvent toxicity for living cells.Abbreviations log P logarithm of P - P solvent partition coefficient in a standard system n-octanol/water     

No oral-cavity-only discrimination of purely olfactory odorants

The purely olfactory odorants coumarin, octanoic acid, phenylethyl alcohol, and vanillin had been found to be consistently identified when presented retronasally but could not be identified when presented oral-cavity only (OCO). However, OCO discrimination of these odorants was not tested. Consequently, it remained possible that the oral cavity trigeminal system might provide sufficient information to differentiate these purely olfactory odorants. To evaluate this, 20 participants attempted to discriminate vapor-phase coumarin, octanoic acid, phenylethyl alcohol, and vanillin and, as a control, the trigeminal stimulus peppermint extract, from their glycerin solvent, all presented OCO. None of the purely olfactory odorants could be discriminated OCO, but, as expected, peppermint extract was consistently discriminated. This inability to discriminate clarifies and expands the previous report of lack of OCO identification of purely olfactory odorants. Taken together with prior data, these results suggest that the oral cavity trigeminal system is fully unresponsive to these odorants in vapor phase and that coumarin, octanoic acid, phenylethyl alcohol, and vanillin are indeed purely olfactory stimuli. The OCO discrimination of peppermint extract demonstrated that the absence of discrimination for the purely olfactory odorants was odorant dependent and confirmed that the oral cavity trigeminal system will provide differential response information to some vapor-phase stimuli.     

大蓟紫外光谱鉴别特征的初步研究

为了研究大蓟(Cirsium japonicum)紫外光谱的显著鉴别特征，以快速、准确地鉴别正品大蓟，采用多溶剂紫外光谱法分析福建省不同地区的自采大蓟和市售18批不同厂家商品大蓟在无水乙醇、氯仿及石油醚溶剂中紫外特征差异，并采用主峰值(含肩峰值)及主谷值的均值加方差归纳比较特征。结果表明，自采大蓟在无水乙醇溶剂中表现为“谷—峰—谷—峰”，即在273±3 nm、326±2 nm处的峰值和250±2 nm、298±1 nm处的谷值具有显著鉴别意义；在氯仿溶剂中，表现为“峰—谷—峰”，即在245±3 nm、273±4 nm处的峰值和260±3 nm处的谷值具有显著鉴别意义；在石油醚溶剂中表现为“肩峰—谷—峰”，即在233±3 nm处的肩峰、265±5 nm处的峰值和257±5 nm处的谷值具有显著鉴别意义。紫外光谱的峰谷特征可用于大蓟鉴别。     

Discrimination between monovalent and divalent cations by hydrophobic solvent-saturated membranes containing fixed negative charges

Summary Cellulose acetate-nitrate filters were saturated with hydrophobic solvent and interposed between various aqueous solutions. The membranes thus formed are cation permselective. The discrimination between a monovalent cation such as K⁺ and the alkaline earth group divalent cations is very sharp. The discrimination ratio is at least a few thousand times in favor of the monovalent cation. A major part of this discrimination is caused by the very low mobility of the divalent cation within the membrane compared with that of the monovalent cation. The remainder of the discrimination is caused by the selectivity of the membranes which prefer monovalent to divalent cations. There is a clear discrepancy between Ba⁺⁺ diffusibility and mobility within, the membrane. This implies that Ba⁺⁺ may move within the hydrophobic membrane as a neutral complex. Some similarity with natural biological membranes is indicated.     

A quantitative method for determining spatial discriminative capacity

Background  

The traditional two-point discrimination (TPD) test, a widely used tactile spatial acuity measure, has been criticized as being imprecise because it is based on subjective criteria and involves a number of non-spatial cues. The results of a recent study showed that as two stimuli were delivered simultaneously, vibrotactile amplitude discrimination became worse when the two stimuli were positioned relatively close together and was significantly degraded when the probes were within a subject's two-point limen. The impairment of amplitude discrimination with decreasing inter-probe distance suggested that the metric of amplitude discrimination could possibly provide a means of objective and quantitative measurement of spatial discrimination capacity.     

Routes to indirect fitness in cooperatively breeding vertebrates: kin discrimination and limited dispersal

Hamilton demonstrated that the evolution of cooperative behaviour is favoured by high relatedness, which can arise through kin discrimination or limited dispersal (population viscosity). These two processes are likely to operate with limited overlap: kin discrimination is beneficial when variation in relatedness is higher, whereas limited dispersal results in less variable and higher average relatedness, reducing selection for kin discrimination. However, most empirical work on eukaryotes has focused on kin discrimination. To address this bias, we analysed how kin discrimination and limited dispersal interact to shape helping behaviour across cooperatively breeding vertebrates. We show that kin discrimination is greater in species where the: (i) average relatedness in groups is lower and more variable; (ii) effect of helpers on breeders reproductive success is greater; and (iii) probability of helping was measured, rather than the amount of help provided. There was also an interaction between these effects with the correlation between the benefits of helping and kin discrimination being stronger in species with higher variance in relatedness. Overall, our results suggest that kin discrimination provides a route to indirect benefits when relatedness is too variable within groups to favour indiscriminate cooperation.     

Quantifying the effects of host discrimination on egg‐laying decision of the cowpea seed beetle,Callosobruchus maculatus

Many parasitic and endophagous insect species are capable of discriminating among the quality of their hosts. However, there is no appropriate way to quantify their discrimination performance. In this study, we quantified how oviposition of the cowpea seed beetle, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae), was affected by the relative contributions of both egg number and host size discrimination. The effect of egg density and resource heterogeneity on these discrimination performances was also explored. Egg‐distribution predictions were made by combining time‐dependent available resource fitness (egg discrimination) and host weight factors (size discrimination). The χ² test was then used for goodness‐of‐fit testing. The effects of both egg and size discrimination on oviposition in environments with different levels of resource heterogeneity were compared. It was found that host size, rather than the number of eggs on the host, plays a larger role in the egg‐laying decision for most individual seed beetles, especially when egg density is high. Host size discrimination behavior was reinforced when the beetles experienced increasing resource heterogeneity, but the performance might reach a plateau. This is the first quantitative evaluation of the effect of host discrimination on egg‐laying decisions of seed beetles.     

Frequency-dependent pollinator discrimination acts against female plants in the gynodioecious Geranium maculatum

MethodsTo test the severity and consequences of this type of pollinator discrimination in Geranium maculatum, experimental populations with the range of sex ratios observed in nature were created, ranging from 13 % to 42 % females. Pollinators were observed in order to measure the strength of discrimination, and pollen deposition and seed production of both sexes were measured to determine the fitness consequences of this discrimination. Additionally a comparison was made across the sex ratios to determine whether discrimination was frequency-dependent.ConclusionsThe results suggest that pollinator discrimination negatively affects females'' relative fitness when they are rare. Thus, the initial spread of females in a population, the first step in the evolution of gynodioecy, may be made more difficult due to pollinator discrimination.     

Difficulties with Pitch Discrimination Influences Pitch Memory Performance: Evidence from Congenital Amusia

Music processing is influenced by pitch perception and memory. Additionally these features interact, with pitch memory performance decreasing as the perceived distance between two pitches decreases. This study examined whether or not the difficulty of pitch discrimination influences pitch retention by testing individuals with congenital amusia. Pitch discrimination difficulty was equated by determining an individual’s threshold with a two down one up staircase procedure and using this to create conditions where two pitches (the standard and the comparison tones) differed by 1x, 2x, and 3x the threshold setting. For comparison with the literature a condition that employed a constant pitch difference of four semitones was also included. The results showed that pitch memory performance improved as the discrimination between the standard and the comparison tones was made easier for both amusic and control groups, and more importantly, that amusics did not show any pitch retention deficits when the discrimination difficulty was equated. In contrast, consistent with previous literature, amusics performed worse than controls when the physical pitch distance was held constant at four semitones. This impaired performance has been interpreted as evidence for pitch memory impairment in the past. However, employing a constant pitch distance always makes the difference closer to the discrimination threshold for the amusic group than for the control group. Therefore, reduced performance in this condition may simply reflect differences in the perceptual difficulty of the discrimination. The findings indicate the importance of equating the discrimination difficulty when investigating memory.     

Energetics of proline racemase: double fractionation experiment, a test for concertedness and for transition-state dominance

To test whether a reaction involving the making and/or breaking of two bonds at two sites is concerted (and proceeds through a single transition state) or is stepwise (and involves a reaction intermediate in which only one bond has been made or broken), we have measured the isotopic fractionation at one site as a function of isotopic substitution at the other site. In the case of proline racemase, the discrimination against solvent deuterium in the product when the reaction is run in mixed H2O-D2O is measured for the reaction both of [2-1H]proline and of [2-2H]proline. The isotopic fractionation at the solvent site may in principle be smaller, the same, or larger, when the 2H-labeled substrate is used rather than the 1H substrate, and--depending upon the nature of the catalyzing groups--this information indicates whether the reaction is stepwise, or concerted, or whether an isotopically insensitive transition state is partially rate determining. Experimentally, we have found that the discrimination against solvent deuterium in the product L-proline is the same, whether D-[2-1H]proline or D-[2-2H]proline is the substrate. This result requires that the substrate and product "on-off" steps are faster than the racemization step and that the racemization reaction proceeds either in a concerted manner or in a stepwise fashion involving enzyme catalytic groups (e.g., thiols) having ground-state fractionation factors around 0.5.     

Pupillary dilation response as an indicator of auditory discrimination in the barn owl

The pupil of an awake, untrained, head-restrained barn owl was found to dilate in response to sounds with a latency of about 25 ms. The magnitude of the dilation scaled with signal-to-noise ratio. The dilation response habituated when a sound was repeated, but recovered when stimulus frequency or location was changed. The magnitude of the recovered response was related to the degree to which habituating and novel stimuli differed and was therefore exploited to measure frequency and spatial discrimination. Frequency discrimination was examined by habituating the response to a reference tone at 3 kHz or 6 kHz and determining the minimum change in frequency required to induce recovery. We observed frequency discrimination of 125 Hz at 3 kHz and 250 Hz at 6 kHz – values comparable to those reported by others using an operant task. Spatial discrimination was assessed by habituating the response to a stimulus from one location and determining the minimum horizontal speaker separation required for recovery. This yielded the first measure of the minimum audible angle in the barn owl: 3° for broadband noise and 4.5° for narrowband noise. The acoustically evoked pupillary dilation is thus a promising indicator of auditory discrimination requiring neither training nor aversive stimuli. Accepted: 28 February 2000     

Reliability criteria of a bioassay using rats trained to detect estrus-specific odor in cow urine

An odor discrimination apparatus was used to quantify the reaction of rats against odor differences of estrous and diestrous urine of cows. Rats were trained to release impulses from a microswitch when they came into contact with estrous but not diestrous urine. After training, the discrimination ability was highly significant (P≤ 0.001) between both urine types. The reaction was specific for cow urine, and no significant discrimination occurred for estrous and diestrous urine from pigs or goats, or that of women. The discrimination of urine diluted with water was still highly significant up to 1:25. Another group of rats was trained to detect camphor. Decreasing concentrations were detected down to 0.1/ug/ml when diluted in water, and down to 1/ug/ml when diluted in estrous urine. Once trained to discriminate between estrous and diestrous urine, rats maintained this ability for 12 mo. Thus, a bioassay was set up to accompany fractionation steps in the laboratory which could lead to the isolation of estrous pheromones in cow urine.     

Perceived Weight Discrimination and Obesity

Weight discrimination is prevalent in American society. Although associated consistently with psychological and economic outcomes, less is known about whether weight discrimination is associated with longitudinal changes in obesity. The objectives of this research are (1) to test whether weight discrimination is associated with risk of becoming obese (Body Mass Index≥30; BMI) by follow-up among those not obese at baseline, and (2) to test whether weight discrimination is associated with risk of remaining obese at follow-up among those already obese at baseline. Participants were drawn from the Health and Retirement Study, a nationally representative longitudinal survey of community-dwelling US residents. A total of 6,157 participants (58.6% female) completed the discrimination measure and had weight and height available from the 2006 and 2010 assessments. Participants who experienced weight discrimination were approximately 2.5 times more likely to become obese by follow-up (OR = 2.54, 95% CI = 1.58–4.08) and participants who were obese at baseline were three times more likely to remain obese at follow up (OR = 3.20, 95% CI = 2.06–4.97) than those who had not experienced such discrimination. These effects held when controlling for demographic factors (age, sex, ethnicity, education) and when baseline BMI was included as a covariate. These effects were also specific to weight discrimination; other forms of discrimination (e.g., sex, race) were unrelated to risk of obesity at follow-up. The present research demonstrates that, in addition to poorer mental health outcomes, weight discrimination has implications for obesity. Rather than motivating individuals to lose weight, weight discrimination increases risk for obesity.     

Three Systems Used for Biocatalysis in Organic Solvents a Comparative Study

The activity and operational stability of horse liver alcohol dehydrogenase (HLADH) and α-chymotrypsin were investigated in three systems commonly used for biocatalysis in organic solvents:

1. enzyme adsorbed on a solid support (celite) and added to the organic solvent (isooctane)

2. enzyme powder directly added to the organic solvent (isooctane).

3. enzyme dissolved in a microemulsion (AOT/isooctane).

The activity and the operational stability in all systems were strongly dependent on the water content. The initial reaction rate was high in both the microemulsion and the celite system, but was much lower when adding the enzymes directly to the organic solvent. HLADH was observed to be more stable when added directly to the organic solvent or dissolved in the microemulsion than when adsorbed on celite, whereas for α-chymotrypsin stability was higher when adsorbed on celite or added directly to the organic solvent. For a hydrolytic reaction, a microemulsion was preferred due to the high water content. When adding the enzymes directly to the organic solvent both HLADH and chymotrypsin were adsorbed strongly to the glass walls of the reaction vessel. None of the systems were superior in all respects for the two enzymes studied.     

Solvent accessibility, residue charge and residue volume, the three ingredients of a robust amino acid substitution matrix

Cost measure matrices or different amino acid indices have been widely used for studies in many fields of biology. One major criticism of these studies might be based on the unavailability of an unbiased and yet effective amino acid substitution matrix. Throughout this study we have devised a cost measure matrix based on the solvent accessibility, residue charge, and residue volume indices. Performed analyses on this novel substitution matrix (i.e. solvent accessibility charge volume (SCV) matrix) support the uncontaminated nature of this matrix regarding the genetic code. Although highly similar to a number of previously available cost measure matrices, the SCV matrix results in a more significant optimality in the error-buffering capacity of the genetic code when compared to many other amino acid substitution matrices. Besides, a method to compare an SCV-based scoring matrix with a number of widely used matrices has been devised, the results of which highlights the robustness of this matrix in protein family discrimination.     

Enantioselective hydrolysis of (R,S)-naproxen 2,2,2-trifluoroethyl ester in water-saturated solvents via lipases from Carica pentagona Heilborn and Carica papaya

A crude lipase prepared from Carica pentagona Heilborn latex was explored as an effective enantioselective biocatalyst for the hydrolytic resolution of (R,S)-naproxen 2,2,2-trifluoroethyl ester in water-saturated organic solvents. Comparisons of the enzyme performance with that from Carica papaya lipase indicated that both lipases showed low tolerance to the hydrophilic solvent and were inhibited by (S)-naproxen and 2,2,2-trifluoroethanol. Improvements on the enzyme activity and enantioselectivty were demonstrated when both lipases in partially purified forms were employed. By using the thermodynamic analysis, the enantiomeric discrimination was mainly driven by the difference of activation enthalpy for all reaction systems except for employing Carica papaya lipase as the biocatalyst for (R,S)-fenoprofen 2,2,2-trifluoroethyl thioester.     

A critical analysis of continuum electrostatics: the screened Coulomb potential--implicit solvent model and the study of the alanine dipeptide and discrimination of misfolded structures of proteins

An analysis of the screened Coulomb potential--implicit solvent model (SCP--ISM) is presented showing that general equations for both the electrostatic and solvation free energy can be derived in a continuum approach, using statistical averaging of the polarization field created by the solvent around the molecule. The derivation clearly shows how the concept of boundary, usually found in macroscopic approaches, is eliminated when the continuum model is obtained from a microscopic treatment using appropriate averaging techniques. The model is used to study the alanine dipeptide in aqueous solution, as well as the discrimination of native protein structures from misfolded conformations. For the alanine dipeptide the free energy surface in the phi--psi space is calculated and compared with recently reported results of a detailed molecular dynamics simulation using an explicit representation of the solvent, and with other available data. The study showed that the results obtained using the SCP--ISM are comparable to those of the explicit water calculation and compares favorably to the FDPB approach. Both transition states and energy minima show a high correlation (r > 0.98) with the results obtained in the explicit water analysis. The study of the misfolded structures of proteins comprised the analysis of three standard decoy sets, namely, the EMBL, Park and Levitt, and Baker's CASP3 sets. In all cases the SCP--ISM discriminated well the native structures of the proteins, and the best-predicted structures were always near-native (cRMSD approximately 2 A).     

HPLC enantioseparation on cellulose tris(3,5-dimethylphenylcarbamate) as a chiral stationary phase: Influences of pore size of silica gel,coating amount,coating solvent,and column temperature on chiral discrimination

Cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) was coated on large-pore silica gels and used as a chiral stationary phase (CSP) for high-performance liquid chromatographic separation of enantiomers. The influences of pore size of silica gel, coating amount of CDMPC, coating solvent, and column temperature on chiral discrimination were investigated. CSPs prepared with a large-pore silica gel having a small surface area showed higher chiral recognition. The amount of CDMPC adsorbed on the silica gel influenced the chiral recognition of some racemates. Loading capacity of racemates increased with an increase of the amount of CDMPC supported on the silica gel, and a CSP coated with 45% CDMPC by weight can be used for both analytical and semi-preparative scale separations. The CDMPC, coated using acetone as the coating solvent, exhibited, in many cases, higher enantioselectivity than that obtained with tetrahydrofuran F as the coating solvent. © 1996 Wiley-Liss, Inc.