Acyltransferase families that act on thioesters: Sequences, structures, and mechanisms.

Acyltransferases (AT) are enzymes that catalyze the transfer of acyl group to a receptor molecule. This review focuses on ATs that act on thioester-containing substrates. Although many ATs can recognize a wide variety of substrates, sequence similarity analysis allowed us to classify the ATs into fifteen distinct families. Each AT family is originated from enzymes experimentally characterized to have AT activity, classified according to sequence similarity, and confirmed with tertiary structure similarity for families that have crystallized structures available. All the sequences and structures of the AT families described here are present in the thioester-active enzyme (ThYme) database. The AT sequences and structures classified into families and available in the ThYme database could contribute to enlightening the understanding acyl transfer to thioester-containing substrates, most commonly coenzyme A, which occur in multiple metabolic pathways, mostly with fatty acids.

Reaction time measures of non-chromatic contamination in opponent stimuli.

Simple visual reaction times (RTs) are highly sensitive to the presence of transient activity. Transient and sustained visual mechanisms generate different RT versus contrast functions because they have different gains. To identify non-chromatic (transient) activity, we can compare RT versus contrast functions obtained with either fast or slow onset stimuli. To test this, the stimulus adopted was a temporal modulation along the red-green axis, introducing non-chromatic components by varying the red-green ratio. The technique was sensitive to departures from isoluminance for all observers; therefore, we present this method as a way to detect transient contamination in a chromatic stimulus.

Medical student misconceptions in cardiovascular physiology.

Students find cardiovascular physiology challenging. Misunderstandings can be due to the nature of the subject, the way it is taught, and prior knowledge, which impede learning of new concepts. Some misunderstood concepts can be corrected with teaching (i.e., preconceptions), whereas others are resistant to instruction (i.e., misconceptions). A set of questions, specifically created by a panel of physiology experts to probe difficult cardiovascular concepts, was used to identify preconceptions, misconceptions, and the effect of education level on question performance. The introductory cardiovascular lecture used in this study was created based on these questions. In-class polling of medical students' (n = 736) performance was performed using the Turning-Point clicker response system during lecture instruction. Results were compared with published data from undergraduates (n = 1,076) who completed the same questions but without prior instruction. To our knowledge, there have been no studies directly comparing performance using the same instrument and large numbers of undergraduate and medical students. A higher education level was associated with increased performance (preconceptions), whereas several concepts resistant to instruction (misconceptions) were identified. Findings suggest that prior knowledge interfered with the acquisition of medical knowledge. Based on these results, potential causes for these misconceptions and remedial teaching suggestions are discussed.

Anomalous pupillary responses to M-cone onsets are linked to ${\rm L}{:}{\rm M}$L:M ratio.

M-cone stimulation induces a pupil constriction to stimulus offset, whereas, with L cones, the pupil responds conventionally with a constriction to onset. To test the possibility that this paradox is linked to the ${\rm L}{:}{\rm M}$L:M ratio, we measured the strength of the effect by injecting a variable amount of positive or negative luminance contamination on either side of M-cone isolation and identifying a balance point at which the pupil responded equally to onset and offset. Nineteen individuals were recruited. In observers with low ${\rm L}{:}{\rm M}$L:M ratio, the paradoxical effect was weak. There was a significant relationship (${{r}^2} = {0.561}$r2=0.561) between the balance point and ${\rm L}{:}{\rm M}$L:M ratio. The effect is likely to be linked to strong inhibitory signals associated with cone-opponent pathways.

IMPAIRED DARK ADAPTATION ASSOCIATED WITH A DISEASED BRUCH MEMBRANE IN PSEUDOXANTHOMA ELASTICUM.

PURPOSE: To characterize dark adaptation in patients with pseudoxanthoma elasticum, a systemic disease leading to calcification of elastic tissue including the Bruch membrane. METHODS: In this prospective case-control study, dark adaptation thresholds were measured using a Goldmann-Weekers dark adaptometer. Additional assessments included best-corrected visual acuity testing, contrast sensitivity, low luminance deficit, and vision-related quality of life. RESULTS: Dark adaptation thresholds were significantly higher, and adaptation periods were prolonged in patients with pseudoxanthoma elasticum (n = 35; 33 with 2 ABCC6 mutations) compared with controls (n = 35). The time to adapt 4 log units (20.6 ± 8.6 vs. 8.0 ± 1.3 minutes) and the mean dark adaptation threshold after 15 minutes (3.5 ± 1.1 vs. 1.8 ± 0.2 log units) were significantly different between patients and controls (both P < 0.001). Low luminance deficits (12.3 ± 6.4 vs. 6.1 ± 4.3 ETDRS letters), contrast sensitivity (1.4 ± 0.3 vs. 1.9 ± 0.1), and low luminance-related quality of life (LLQ score: 1,286 ± 355 vs. 2,167 ± 68) were also significantly worse in patients with pseudoxanthoma elasticum (all, P < 0.001). Two patients were treated with high-dose vitamin A which partially reversed impaired dark adaptation. CONCLUSION: Patients with pseudoxanthoma elasticum often have impaired dark adaptation. Positive effects of vitamin A supplementation may indicate restricted retinal access of vitamin A through the Bruch membrane as one possible underlying pathogenic factor.

Speed and accuracy of saccades in patients with glaucoma evaluated using an eye tracking perimeter.

BACKGROUND: To examine the speed and accuracy of saccadic eye movements during a novel eye tracking threshold visual field assessment and determine whether eye movement parameters may improve ability to detect glaucoma. METHODS: A prospective study including both eyes of 31 patients with glaucoma and 23 controls. Standard automated perimetry (SAP) and eye tracking perimetry (saccadic vector optokinetic perimetry, SVOP) was performed. SVOP provided data on threshold sensitivity, saccade latency, and two measures of accuracy of saccades (direction bias and amplitude bias). The relationship between eye movement parameters and severity of glaucoma was examined and Receiver Operating Characteristic curves were used to assess ability to detect glaucoma. RESULTS: Patients with glaucoma had significantly slower saccades (602.9 ± 50.0 ms versus 578.3 ± 44.6 ms for controls, P = 0.009) and reduced saccade accuracy (direction bias = 7.4 ± 1.8 versus 6.5 ± 1.5 degrees, P = 0.006). There was a significant slowing of saccades and saccades became less accurate with worsening SAP sensitivity. Slower saccades were associated with increased odds of glaucoma; however, the AUC for saccade latency was only 0.635 compared to 0.914 for SVOP sensitivity. CONCLUSION: Patients with glaucoma had significant differences in eye movements compared to healthy subjects, with a relationship between slower and less accurate eye movements and worse glaucoma severity. However, in a multivariable model, eye movement parameters were not of additional benefit in differentiating eyes with glaucoma from healthy controls.

Chromatic fading following complete adaptation to unique hues.

Profound vision loss occurs after prolonged exposure to an unchanging featureless visual environment. The effect is sometimes called visual fade. Here we investigate this phenomenon in the color domain using two different experiments. In the first experiment we determine the time needed for a colored background to appear achromatic. Four backgrounds were tested. Each represented the observers' four unique hues. This adaptation time was compared with time to recover after adaptation Hue shifts at the end of the adaptation period were also measured. There were wide individual differences in adaptation times and recovery times. Overall recovery was faster than adaptation (p < 0.02). There were minimal shifts in hue. In the second experiment the changes in saturation (Munsell chroma) and lightness (Munsell value) of the background were monitored at six time intervals during the adapting process. Again asymmetric matching with Munsell samples was used. There were two distinct components to both the adaptation and recovery phases; one fast with time constant <1s, the other slow with time constant between 40 and 160s. The experiments show that the special case of visual fade involving color represents the sensory basis for many color-related effects involving adaptation.

Using lectures to identify student misconceptions: a study on the paradoxical effects of hyperkalemia on vascular smooth muscle.

Medical students have difficulty understanding the mechanisms underlying hyperkalemia-mediated local control of blood flow. Such control mechanisms are crucial in the brain, kidney, and skeletal muscle vasculature. We aimed to identify medical students' misconceptions via assessment of students' in-class knowledge and, subsequently, improve future teaching of this concept. In-class polling was performed with the TurningPoint clicker response system (n = 860) to gauge students' understanding of three physiological concepts related to hyperkalemia: membrane potential (Vm), conductance, and smooth muscle response. Vm includes the concepts of equilibrium potential (Veq) for specific ions, as well as driving force (DF = Vm - Veq). Students understood the concept of DF (~70% answered correctly), suggesting their understanding of Vm. However, students misunderstood that hyperkalemia results in depolarization (~52% answered correctly) and leads to an increase in potassium conductance (~31% answered correctly). Clarification of the type of smooth muscle as vascular increased the percentage of correct responses (~51 to 73%). The data indicate that students lacked knowledge of specific potassium conductance in various muscle types, resulting in divergent responses, such as the canonical depolarization in skeletal muscle versus hyperpolarization in smooth muscle cells during hyperkalemia. Misunderstanding of this crucial concept of conductance is directly related to the students' performance. Furthermore, we connected the paradoxical effect of hyperkalemia to pathological acute and chronic hyperkalemia clinical scenarios.

Effect of a small-group, active learning, tutorial-based, in-course enrichment program on student performance in medical physiology.

Physiology is one of the major foundational sciences for the medical curriculum. This discipline has proven challenging for students to master due to ineffective content acquisition and retention. Preliminary data obtained from a survey completed by "low-performance" students (those maintaining a grade average below the passing mark of 70%) at Morehouse School of Medicine reported that students lacked the ability to adequately recognize and extract important physiological concepts to successfully navigate multiple-choice assessments. It was hypothesized that a specially designed, small-group, active learning, physiology in-course enrichment program would minimize course assessment failure rates by enhancing the ability of low-performance students to effectively identify important course content, successfully perform on multiple-choice assessments, and, thereby, improve overall course performance. Using self-report surveys, study skills and test-taking deficiencies limiting successful comprehension of course material and examination performance were identified. Mini-quiz assessments and assignments in formulating multiple-choice examination questions were given to help students recognize and solidify core concepts and improve test-taking ability. Lastly, self-report surveys evaluated the effectiveness of the enrichment program on overall course performance. Results showed a marked improvement in student confidence levels with regards to approaching multiple-choice assessments, and a significant improvement in grades achieved in the physiology component of the first-year curriculum, as 100% of participants achieved a final passing grade average of ≥70%. It was concluded that students became more proficient in identifying, understanding, and applying core physiological concepts and more successful in mastering multiple-choice questions.

Paradoxical pupil responses to isolated M-cone increments.

M-cone onsets appear dimmer than the background and elicit electroretinograms (ERGs) resembling the light offset response. We sought a corresponding anomalous pupillary light reflex (PLR) using a 4-primary ganzfeld as stimulator and pupillometer. Increments and decrements of white light were compared with M- and L-cone onsets and offsets using silent substitution. Luminance bias (LB) could be added to or subtracted from the cone-isolating stimuli. There was a normal PLR to L-cone increments, but the pupil constricted mainly to M-cone decrements. Changing LB produced a neutral point where on and off responses were balanced. The results reflect ERG and psychophysical studies. This observation may be linked to the antagonistic nature of the M-cone input to cone opponent mechanisms.

Chips in the sunshine: color constancy with real versus simulated Munsell chips under illuminants adjacent to the daylight locus.

Accurate color judgments rely on a powerful cognitive component. Here we compare the performance of color constancy under real and simulated conditions. Shifts in the u'v' color plane induced by illuminant A (2750 K) and illuminant S (>20,000 K) were measured using asymmetric color matching. A general linear model was used to predict performance from the following dependent variables: chroma ("4" and "6"), illuminant ("A" and "S"), presentation mode ("Real" and "Monitor"), and hue zone ("blue," "green," "yellow," "red," and "purple"). There was a strong overall effect [F(7,264)=78.65, p<0.001]. Post hoc analysis showed that performance was substantially superior under real [chromatic constancy index (cCI)=0.76] compared with simulated cCI=0.55) conditions.

Slowed dark adaptation in older eyes; effect of location.

PURPOSE: The rate of rod sensitivity recovery following a photobleach is a basic measure of the integrity of the outer retina. Rods are selectively impaired in aging and many disorders of the retina, notably Age-Related Macular Degeneration (AMD). It is not known for certain whether the age-related deficit is a pan-retinal effect or if there are localised regions of impaired rod function. To address this important issue a dual arc stimulus was developed that samples sensitivity recovery in two retinal locations. METHODS: Arc-shaped stimuli were presented on a black CRT screen at two locations, in the inferior visual field. Following a bleach, which was localised to the stimuli, recovery of sensitivity was measured using a modified method of adjustment technique. Neutral density filters were used to extend the luminance range of the CRT. Sensitivity recovery functions were fitted by non-linear regression to a seven-parameter model. RESULTS: Pairs of sensitivity recovery functions were generated from the stimuli. The cone phases of these functions were identical. The slopes of the S2 sections of the curves were steeper for the outer stimuli for both young (p < 0.001) and older (p = 0.003) observers. The difference between the two was the same for the two groups. The α point was reached slightly earlier for the young observers and with the outer stimulus but neither of these effects reached statistical significance. The ß point occurred earlier for the outer stimuli and this effect was statistically significant only for the older group. CONCLUSIONS: The method places minimal demands on observers. The fact that rod sensitivity recovery is slowed in the older normal eye to the same extent in the two locations suggests that this deficit may be uniform across the retina. As there are localised losses in scotopic function in AMD, the technique is ideally suited to distinguishing impaired recovery dynamics due to normal ageing from those caused by disease.

Preterm birth is associated with atypical social orienting in infancy detected using eye tracking.

BACKGROUND: Preterm birth is closely associated with neurocognitive impairment in childhood including increased risk for social difficulties. Eye tracking objectively assesses eye-gaze behaviour in response to visual stimuli, which permits inference about underlying cognitive processes. We tested the hypothesis that social orienting in infancy is altered by preterm birth. METHODS: Fifty preterm infants with mean (range) gestational age (GA) at birth of 29(+1) (23(+2) -33(+0) ) weeks and 50 term infants with mean (range) GA at birth 40(+2) (37(+0) -42(+3) ) weeks underwent eye tracking at median age of 7 months. Infants were presented with three categories of social stimuli of increasing complexity. Time to first fixate (TFF) and looking time (LT) on areas of interest (AoIs) were recorded using remote eye tracking. RESULTS: Preterm infants consistently fixated for a shorter time on social content than term infants across all three tasks: face-scanning (fixation to eyes minus mouth 0.61s vs. 1.47s, p = .013); face pop-out task (fixation to face 0.8s vs. 1.34s, p = .023); and social preferential looking (1.16s vs. 1.5s p = .02). Time given to AoIs containing social content as a proportion of LT at the whole stimulus was lower in preterm infants across all three tasks. These results were not explained by differences in overall looking time between the groups. CONCLUSIONS: Eye tracking provides early evidence of atypical cognition after preterm birth, and may be a useful tool for stratifying infants at risk of impairment for early interventions designed to improve outcome.

A Hantzsch Amido Dihydropyridine as a Transfer Hydrogenation Reagent for α,ß-Unsaturated Ketones.

An improved synthesis of the bis-methylamido Hantzsch dihydropyridine is described. The Hantzsch amide is demonstrated to be an effective transfer hydrogenation reagent using α,ß-unsaturated ketones as the test case. Unreacted Hantzsch amide and the bis-methylamidopyridine byproduct are effectively removed by extraction in contrast to the commonly used Hantzsch diethyl ester. Several examples are given with the reaction being more effective for conjugated aromatic substrates than for aliphatics.

Improving the analytical performance and versatility of paper spray mass spectrometry via paper microfluidics.

Two paper-based microfluidic techniques, photolithography and wax patterning, were investigated for their potential to improve upon the sensitivity, reproducibility, and versatility of paper spray mass spectrometry. The main limitation of photolithography was the significant signal (approximately three orders of magnitude) above background which was attributed to the chemicals used in the photoresist process. Hydrophobic barriers created via wax patterning were discovered to have approximately 2 orders of magnitude less background signal compared to analogous barriers created using photolithography. A minimum printed wax barrier thickness of approximately 0.3 mm was necessary to consistently retain commonly used paper spray solvents (1 : 1 water : acetonitrile/methanol) and avoid leakage. Constricting capillary flow via wax-printed channels yielded both a significant increase in signal and detection time for detection of model analytes. This signal increase, which was attributed to restricting the radial flow of analyte/solvent on paper (i.e., a concentrating effect), afforded a significant increase in sensitivity (p ≪ 0.05) for the detection of pesticides spiked into residential tap water using a five-point calibration curve. Finally, unique mixing designs using wax patterning can be envisioned to perform on-paper analyte derivatization.

A dim view of M-cone onsets.

We investigated the brightness (i.e., perceived luminance) of isolated L- and M-cone pulses to seek a perceptual correlate of our previous reports that M-on electroretinograms resemble L-off responses, implying the operation of post-receptoral opponent processing. Using triple silent substitutions, cone increments were generated in a 4-primary ganzfeld, masked by random positive or negative luminance bias. The results show that M-cone increments decrease in brightness, while L-cone increments increase. These differences became smaller as field size reduced; this was not eccentricity or area dependent. We speculate about early retinal input into brightness perception.

Spatial properties of L- and M-cone driven incremental (On-) and decremental (Off-) electroretinograms: evidence for the involvement of multiple post-receptoral mechanisms.

An overview of electroretinogram response components to incremental and decremental steps in L- and M-cone excitation was obtained in human observers, while varying the spatial properties of the stimulus. Responses to L- and M-cone stimuli of opposite polarity resembled each other, particularly within the central 35° of the retina. All amplitudes grew as stimulus size increased; however, earlier and later components of the On- and Off-responses showed differing degrees of dependency on stimulus size. Thus, they may reflect different proportions of responses originating in parvocellular (less stimulus size-dependent) and magnocellular (more stimulus size-dependent) streams.

Development and testing of an automated computer tablet-based method for self-testing of high and low contrast near visual acuity in ophthalmic patients.

PURPOSE: Many eye diseases require on-going assessment for optimal management, creating an ever-increasing burden on patients and hospitals that could potentially be reduced through home vision monitoring. However, there is limited evidence for the utility of current applications and devices for this. To address this, we present a new automated, computer tablet-based method for self-testing near visual acuity (VA) for both high and low contrast targets. We report on its reliability and agreement with gold standard measures. METHODS: The Mobile Assessment of Vision by intERactIve Computer (MAVERIC) system consists of a calibrated computer tablet housed in a bespoke viewing chamber. Purpose-built software automatically elicits touch-screen responses from subjects to measure their near VA for either low or high contrast acuity. Near high contrast acuity was measured using both the MAVERIC system and a near Landolt C chart in one eye for 81 patients and low contrast acuity using the MAVERIC system and a 25 % contrast near EDTRS chart in one eye of a separate 95 patients. The MAVERIC near acuity was also retested after 20 min to evaluate repeatability. RESULTS: Repeatability of both high and low contrast MAVERIC acuity measures, and their agreement with the chart tests, was assessed using the Bland-Altman comparison method. One hundred and seventy-three patients (96 %) completed the self- testing MAVERIC system without formal assistance. The resulting MAVERIC vision demonstrated good repeatability and good agreement with the gold-standard near chart measures. CONCLUSIONS: This study demonstrates the potential utility of the MAVERIC system for patients with ophthalmic disease to self-test their high and low contrast VA. The technique has a high degree of reliability and agreement with gold standard chart based measurements.

Psychometric properties of the Jefferson Scale of Empathy-Health Professional Student's version: An Italian validation study with nursing students.

This methodological study was conducted to test the psychometric properties of the Jefferson Scale of Empathy-Health Professional Student's version (JSE-HPS), in a convenience sample of 797 Italian nursing students and to describe their empathic engagement. Data were subjected to exploratory and confirmatory factor analysis, test-retest, correlation analysis, t-test, and analysis of variance method. Principal component factor extraction with Oblimin rotation on the first half of the sample was conducted. The analysis suggested a three-factor solution for 14 items: "compassionate care/emotional engagement," "perspective-taking," and "standing in the patient's shoes." Confirmatory factor analysis on the second half of the sample showed good fit indexes for the 14-item solution, indicated by the exploratory factor analysis, and the 20 item solution of the scale, with the exception of one item. Test-retest correlation was 0.50 (P < 0.001) for the overall scale. Results from group comparisons and correlations are also provided and discussed. The Italian version of the JSE-HPS is a psychometrically sound tool. The translated 20-item solution is also suitable to carry out cross-cultural comparisons.

The maize lipoxygenase, ZmLOX10, mediates green leaf volatile, jasmonate and herbivore-induced plant volatile production for defense against insect attack.

Fatty acid derivatives are of central importance for plant immunity against insect herbivores; however, major regulatory genes and the signals that modulate these defense metabolites are vastly understudied, especially in important agro-economic monocot species. Here we show that products and signals derived from a single Zea mays (maize) lipoxygenase (LOX), ZmLOX10, are critical for both direct and indirect defenses to herbivory. We provide genetic evidence that two 13-LOXs, ZmLOX10 and ZmLOX8, specialize in providing substrate for the green leaf volatile (GLV) and jasmonate (JA) biosynthesis pathways, respectively. Supporting the specialization of these LOX isoforms, LOX8 and LOX10 are localized to two distinct cellular compartments, indicating that the JA and GLV biosynthesis pathways are physically separated in maize. Reduced expression of JA biosynthesis genes and diminished levels of JA in lox10 mutants indicate that LOX10-derived signaling is required for LOX8-mediated JA. The possible role of GLVs in JA signaling is supported by their ability to partially restore wound-induced JA levels in lox10 mutants. The impaired ability of lox10 mutants to produce GLVs and JA led to dramatic reductions in herbivore-induced plant volatiles (HIPVs) and attractiveness to parasitoid wasps. Because LOX10 is under circadian rhythm regulation, this study provides a mechanistic link to the diurnal regulation of GLVs and HIPVs. GLV-, JA- and HIPV-deficient lox10 mutants display compromised resistance to insect feeding, both under laboratory and field conditions, which is strong evidence that LOX10-dependent metabolites confer immunity against insect attack. Hence, this comprehensive gene to agro-ecosystem study reveals the broad implications of a single LOX isoform in herbivore defense.