Inhibition Predicts the Course of Depression and Anxiety Symptoms Among Adolescents: The Moderating Role of Familial Risk

ABSTRACT

Numerous theoretical models suggest that inhibition difficulties-the inability to moderate automatic responses-contribute to the onset and/or maintenance of internalizing symptoms. Inhibition deficits and internalizing disorders run in families and share overlapping genetic risk factors, suggesting that inhibition deficits may be particularly prognostic of internalizing symptoms in those with high familial risk. This study tested this hypothesis in a longitudinal sample during the transition from adolescence to early adulthood. As hypothesized, prospective associations between inhibition and anxiety and depressive symptoms 8 years later were moderated by familial risk for depression. Specifically, poorer inhibition prospectively predicted greater anxiety and depressive symptoms in those at high (but not low) familial risk for major depressive disorder. These findings provide preliminary support for impaired inhibition as an indicator of risk for later internalizing symptoms in those at high familial risk.

Associations Between Repetitive Negative Thinking and Habituation of Defensive Responding Within and Between Sessions

Repetitive negative thinking (RNT) is a transdiagnostic risk factor for internalizing psychopathology, and theoretical models suggest that RNT may maintain symptoms by interfering with psychophysiological habituation. The present study therefore examined associations between RNT and habituation within and between study sessions. Community members (N=86) completed a habituation task involving exposure to acoustic probes at up to five sessions spaced 7 days apart on average. Eyeblink startle response was measured using the electromyography startle magnitude. Self-reported anxiety was assessed before and after the habituation task at each session. Multilevel growth curve modeling indicated that RNT was associated with a higher "floor" (i.e., asymptote) of startle responding as evidenced by reduced within-session startle habituation at later sessions. Results suggest that RNT may disrupt startle habituation and are consistent with theoretical models proposing that RNT sustains physiological activation to support avoidance of negative emotional contrasts or perceived future threats.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42761-022-00121-w.

The roles of disgust sensitivity and anxiety sensitivity in attentional bias in dental anxiety

Individuals with dental anxiety show biased attentional processing of threat- and dental-related information. Disgust sensitivity and anxiety sensitivity are both associated with dental fears and attentional biases. Whereas disgust sensitivity is generally associated with attentional avoidance (Armstrong et al., 2014), anxiety sensitivity may be associated with attentional engagement (Keogh et al., 2001a). Elucidating the role of these constructs in dental anxiety-relevant attentional biases could inform theoretical models and/or intervention recommendations. Participants (N = 51) with high dental anxiety completed a Posner paradigm to assess attentional biases to dental versus neutral stimuli. We examined whether disgust sensitivity and anxiety sensitivity moderated degree of attentional bias. Results indicated that both disgust sensitivity (mutilation subscale) and anxiety sensitivity (physical concerns subscale) statistically moderated degree of attentional bias at trend level, and in opposite directions. Simple effects analyses further indicated that disgust sensitivity regarding mutilation was associated with less attentional bias toward dental relative to neutral stimuli, potentially indicating attentional avoidance, and remained so when adjusting for anxiety sensitivity. In contrast, simple effects analysis indicated that anxiety sensitivity regarding physical concerns was not associated with magnitude of attentional bias. If replicated, findings highlight the potential role of disgust in dental anxiety.

The emotion-elicited late positive potential is stable across five testing sessions

Many studies have examined associations between neural and behavioral markers of attention to emotion and individual differences in affective functioning. However, the majority of these studies are cross-sectional, and examine associations between brain, behavior, and individual differences at one or two time-points, limiting our understanding of the extent to which these neural responses reflect trait-like patterns of attention. The present study used the Emotional Interrupt paradigm, and examined the stability and trajectory of behavioral (i.e., reaction time to targets following task-irrelevant appetitive, neutral, and aversive images), and neural responses to images (i.e., the late positive potential or LPP), across five sessions separated by one week in 86 individuals. Additionally, we examined the extent to which the LPP and behavioral measures were sensitive to naturally occurring daily fluctuations in positive and negative affect. Results indicate that, though the magnitude of the conditional LPP waveforms decreased over time, the degree of emotional modulation (i.e., differentiation of emotional from neutral) did not; in fact, differentiation of appetitive from neutral increased over time. Behavioral responses were similarly stable across sessions. Additionally, we largely did not observe significant effects of state positive and negative affect on the LPP or behavior over time. Finally, the LPP elicited by appetitive images significantly predicted reaction time to targets following these images. These data suggest that neural and behavioral markers of attention to motivationally salient cues may be trait-like in nature, and may be helpful in future studies seeking to identify markers of vulnerability for diverse forms of psychopathology.

Mobile applications may be the future of veteran mental health support but do veterans know yet? A survey of app knowledge and use

Given the substantial investment in the development of mental health mobile applications (apps), information about penetration in the patient populations of interest is critical. This study describes the proportion of veterans who are knowledgeable of and utilize the Department of Veteran Affairs (VA) and Department of Defense (DoD) mental health apps. A cross-sectional survey of 140 veterans was conducted in primary care and outpatient mental health clinics at a large VA facility. Ninety-one percent of veterans (n = 127) reported smartphone ownership. Of these, 42.5% and 20.4% had heard of and used at least one of the 22 VA/DoD mental health apps, respectively. When veterans were asked to pick the individual VA/DoD apps they had previously used from a list, the proportion of participants who reported prior use ranged from 0% (Moving Forward) to 6.5% (Mindfulness Coach). Treatment for psychiatric problems relevant to the apps did not predict veteran knowledge/use of the VA/DoD apps. Rates of app use remained low among veterans reporting symptoms/diagnoses apps were designed to address (e.g., 7.5% of veterans who reported posttraumatic stress disorder (PTSD) had used PTSD Coach). The most common barrier to app use (endorsed by 65.7% of participants) was awareness of the apps. Expansion of existing VA/DoD efforts to educate patients and providers treating relevant conditions is indicated. Evaluation of evidence-based mobile health support specialists in clinical settings may also be indicated. This study provides critical information to guide future dissemination efforts and to help evaluate the impact of investments to date. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Posttraumatic Stress Disorder Symptom Cluster Structure in Prolonged Exposure Therapy and Virtual Reality Exposure

The emotional processing theory of posttraumatic stress disorder (PTSD) posits that avoidance is central to PTSD development and maintenance. Prolonged exposure (PE) therapy, which clinically focuses on avoidance reduction, has strong empirical support as a PTSD treatment. Virtual reality exposure (VRE) has been utilized to accelerate avoidance reduction by increasing multisensory engagement. Although some exposure therapy studies have found associations between avoidance and PTSD symptoms, others have indicated that reexperiencing or hyperarousal symptoms drive symptom trajectories. Using a cross-lagged panel design, the present secondary data analysis examined temporal associations between clinician-assessed PTSD symptom clusters during treatment with PE, VRE, or a waitlist control condition. There were no significant differences between PE and VRE regarding symptom clusters at any assessment. Compared to the waitlist condition, individuals who received VRE or PE exhibited earlier reductions in avoidance/numbing symptoms, β = -.19, 95% CI [-.33, -.05], followed by reductions in hyperarousal symptoms, β = -.21, 95% CI [-.33, -.09]. Hyperarousal symptoms predicted changes in later avoidance/numbing and reexperiencing outcomes across treatment: pretreatment to midtreatment, β = .29, 95% CI [.17, .42]; midtreatment to posttreatment, β = .23, 95% CI [.07, .39]. Reexperiencing symptoms predicted changes in hyperarousal outcomes earlier in treatment, β = .22, 95% CI [.02, .37], whereas avoidance/numbing symptoms predicted changes in hyperarousal outcomes later in treatment, β = .18, 95% CI [.04, .32]. These findings support the efficacy of exposure therapy in addressing avoidance/numbing symptoms and highlight the potential importance of hyperarousal symptoms in relation to other symptom clusters.

Concreteness of thoughts and images during suppression and expression of worry

The avoidance theory of worry (Borkovec, Alcaine, & Behar, 2004) posits that the verbal-linguistic (versus imagery-based) nature of worry elicits abstract (versus concrete) processing, which inhibits affective responding and generates a host of negative consequences. Although suppression of worrisome thinking is maladaptive (Purdon, 1999), expression of worry using vivid imagery may increase concreteness of worrisome thinking and facilitate more adaptive emotional responding. The present study examined whether the valence, content, and expression of mentation impacts concreteness of thought. Participants (N = 62) were randomly assigned to verbalize their thoughts while engaging in either verbal-linguistic- or imagery-based mentation about both worrisome and neutral topics. Participants were also randomly assigned to engage in a 5-min period of suppressing or expressing the target stimuli before engaging in 5-min of freely expressing the targets. Verbalizations of mental content were coded for level of abstractness/concreteness. For neutral stimuli, imagery-based mentation led to greater concreteness than did verbal-linguistic mentation; however, for worrisome stimuli, imagery-based mentation did not enhance concreteness. In addition, for neutral (but not worrisome) stimuli, an initial period of suppression was associated with increased concreteness during subsequent expression. Imagery-based mentation about worrisome stimuli may not enhance concreteness; moreover, unlike suppression of neutral stimuli, suppression of worrisome stimuli may maintain, rather than ameliorate, abstractness of thought.

Startle during threat longitudinally predicts functional impairment independent of DSM diagnoses

Heightened responsivity to unpredictable, and perhaps predictable, threat characterizes some internalizing disorders and may be vulnerability factors for psychopathology as well. However, few studies have directly tested whether individual differences in unpredictable and/or predictable threat responding longitudinally predict symptoms of psychopathology and functional outcomes. Examining functioning is particularly important given that functioning is separable from symptoms of psychopathology. The present study examined whether electromyography startle measures of predictable and/or unpredictable threat responding was associated with interviewer-assessed symptoms of internalizing psychopathology and functional impairment at baseline (n = 409) and one-year follow-up (n = 104). Elevated startle responding to unpredictable and predictable threat longitudinally predicted a worsening of functioning over time and this effect was independent of change of symptoms over time. Importantly, threat responding at baseline predicted functional impairment during the follow-up independent of the effects of DSM-defined fear-based (e.g., panic disorder) or distress-misery (e.g., major depressive disorder) internalizing disorders. These findings provide initial support for the incremental validity of neurobiological vulnerability markers of threat responding over and above DSM disorders and highlight the importance of distinguishing functional outcomes from symptom outcomes.

Enhancing the Efficacy of Cognitive Bias Modification for Social Anxiety

Cognitive bias modification for interpretation (CBM-I) is a promising treatment modality for social anxiety disorder, but effect sizes are relatively small across investigations (Hallion & Ruscio, 2011). Additionally, the extent to which CBM-I impacts other cognitive, emotional, and behavioral outcomes is unclear. This study investigated whether two empirically supported treatment components for anxiety disorders, imaginal exposure (IE) and relaxation, augment the effects of CBM-I and increase the extent to which the effects of CBM-I generalize to behavioral and affective outcomes. We randomly assigned 111 undergraduate students with social anxiety to undergo IE, relaxation, or neutral thinking prior to CBM-I, then measured their interpretation biases, as well as their speaking time, anxiety, and subjective evaluations of performance during a speech task. Results indicated that individuals who received IE prior to CBM-I evidenced more adaptive interpretation biases and less behavioral avoidance during the speech task than did individuals who engaged in relaxation or neutral thinking. However, they did not report differential anxiety, habituation, or evaluations of their performance on the speech task. These findings suggest that the combination of CBM-I with adjunct components that target behavioral, rather than cognitive, mechanisms can facilitate transfer of the effects of CBM-I to reducing behavioral avoidance.

The effect of panic disorder versus anxiety sensitivity on event-related potentials during anticipation of threat

Attention-related abnormalities are key components of the abnormal defensive responding observed in panic disorder (PD). Although behavioral studies have found aberrant attentional biases towards threat in PD, psychophysiological studies have been mixed. Predictability of threat, an important feature of threat processing, may have contributed to these mixed findings. Additionally, anxiety sensitivity, a dimensional trait associated with PD, may yield stronger associations with cognitive processes than categorical diagnoses of PD. In this study, 171 participants with PD and/or depression and healthy controls completed a task that differentiated anticipation of predictable vs. unpredictable shocks, while startle eyeblink and event-related potentials (ERPs [N100, P300]) were recorded. In all participants, relative to the control condition, probe N100 was enhanced to both predictable and unpredictable threat, whereas P300 suppression was unique to predictable threat. Probe N100, but not P300, was associated with startle eyeblink during both threatening conditions, and was strongest for unpredictable threat. PD was not associated with ERPs, but anxiety sensitivity (physical concerns) was positively associated with probe N100 (indicating reduced responding) in the unpredictable condition independent of PD diagnosis. Vulnerability to panic-related psychopathology may be characterized by aberrant early processing of threat, which may be especially evident during anticipation of unpredictable threats.

The Effects of Worry and Relaxation on Flexibility During Cognitive Restructuring

Worry is associated with inflexibility in cognitive, emotional, and physiological functioning. In addition, worry’s negative valence and abstract level of construal are rigid characteristics that contribute to its nonadaptive consequences. Relaxation and cognitive therapy aim to increase flexibility in chronic worriers, and may have greater efficacy when administered in combination. We examined the extent to which relaxation enhances and/or worry inhibits cognitive flexibility during a cognitive restructuring exercise in which participants generated alternative predictions for their worries. Participants ( n = 189) were randomly assigned to engage in relaxation, worry, or neutral thinking prior to cognitive restructuring. We measured the number and perceived likelihood of alternative predictions generated by participants, and coded those alternative predictions for their degree of positive valence, negative valence, and level of construal (abstractness to concreteness). Worry and relaxation did not lead to different numbers or perceived likelihood of alternative predictions. However, compared with participants with minimal symptoms of generalized anxiety disorder (GAD), those with elevated symptoms of GAD who engaged in prior worry generated alternative predictions characterized by greater negative valence and more abstractness (i.e., less concreteness). We also found that greater negative valence of alternative predictions was associated with more abstractness, whereas greater positive valence of alternative predictions was associated with more concreteness. These findings suggest that after engaging in worry, individuals with GAD may be less able to flexibly shift from the use of nonadaptive characteristics (negative valence, abstractness) associated with feared outcomes to the use of more adaptive characteristics (positive valence, concreteness) when considering alternative predictions.

Concreteness of idiographic worry and anticipatory processing

BACKGROUND AND OBJECTIVES

Worry and anticipatory processing are forms of repetitive negative thinking (RNT) that are associated with maladaptive characteristics and negative consequences. One key maladaptive characteristic of worry is its abstract nature (Goldwin & Behar, 2012; Stöber & Borkovec, 2002). Several investigations have relied on inductions of worry that are social-evaluative in nature, which precludes distinctions between worry and RNT about social-evaluative situations. The present study examined similarities and distinctions between worry and anticipatory processing on potentially important maladaptive characteristics.

METHODS

Participants (N = 279) engaged in idiographic periods of uninstructed mentation, worry, and anticipatory processing and provided thought samples during each minute of each induction. Thought samples were assessed for concreteness, degree of verbal-linguistic activity, and degree of imagery-based activity.

RESULTS

Both worry and anticipatory processing were characterized by reduced concreteness, increased abstraction of thought over time, and a predominance of verbal-linguistic activity. However, worry was more abstract, more verbal-linguistic, and less imagery-based relative to anticipatory processing. Finally, worry demonstrated reductions in verbal-linguistic activity over time, whereas anticipatory processing demonstrated reductions in imagery-based activity over time.

LIMITATIONS

Worry was limited to non-social topics to distinguish worry from anticipatory processing, and may not represent worry that is social in nature. Generalizability may also be limited by use of an undergraduate sample.

CONCLUSIONS

Results from the present study provide support for Stöber's theory regarding the reduced concreteness of worry, and suggest that although worry and anticipatory processing share some features, they also contain characteristics unique to each process.

How many blinks are necessary for a reliable startle response? A test using the NPU-threat task

Emotion-modulated startle is a frequently used method in affective science. Although there is a growing literature on the reliability of this measure, it is presently unclear how many startle responses are necessary to obtain a reliable signal. The present study therefore evaluated the reliability of startle responding as a function of number of startle responses (NoS) during a widely used threat-of-shock paradigm, the NPU-threat task, in a clinical (N=205) and non-clinical (N=92) sample. In the clinical sample, internal consistency was also examined independently for healthy controls vs. those with panic disorder and/or major depression and retest reliability was assessed as a function of NoS. Although results varied somewhat by diagnosis and for retest reliability, the overall pattern of results suggested that six startle responses per condition were necessary to obtain acceptable reliability in clinical and non-clinical samples during this threat-of-shock paradigm in the present study.

Perception of active and passive turning in Parkinson disease

BACKGROUND

Many individuals with Parkinson disease (PD) experience difficulty with turning, yet little is known about the reasons for this difficulty.

OBJECTIVE

The authors sought to determine whether individuals with PD can use visual, vestibular, and proprioceptive cues to estimate how far they have turned.

METHODS

Fifteen PD subjects and 11 controls performed active and passive turns to the left and right, with and without vision, with amplitudes of 90, 180, 270, and 360 degrees. For active conditions, subjects were told the direction and amplitude of the desired turn and then attempted to turn in place the specified amount via actively stepping. For passive conditions, subjects were told that the disc they stood on would turn and they were to press a button when they had traveled the specified amplitude.

RESULTS

There were no differences between PD and control groups in any of the conditions, suggesting that those with PD effectively used sensory cues available in the different conditions to accurately judge distance turned. The authors found no apparent deficits in the visual, vestibular, or proprioceptive systems or in integration of these senses for performance of the turning task tested.

CONCLUSIONS

Turning difficulties associated with PD may more likely relate to motor or sensorimotor integration deficits than to pure sensory or sensory integration deficits. Generalizability of the study may be limited by the fact that subjects were tested at a single velocity for passive rotations, were on medication, and had relatively mild PD (primarily H&Y 2).

Changes in perception of active but not passive turning following stepping on the rotating treadmill

The purpose of this work was to determine whether walking on a rotating disc would cause changes in perception of active and passive turning. Ten healthy control subjects wore a blindfold and earplugs while completing trials of active and passive turning. For active conditions, subjects were told the direction and amplitude of the desired turn and then attempted to turn in place the specified amount via actively stepping. For passive conditions, subjects were told that the disc they stood on would turn and they were to press a button when they had traveled the specified amplitude. Subjects completed active and passive trials to the left and right with amplitudes of 90, 180, 270, and 360 degrees. Subjects then stepped in place for 15 min on a disc rotating clockwise at 90 degrees /s, after which they repeated the trials of active and passive turning. Following rotating treadmill stimulation, subjects asked to turn in the direction opposite disc rotation (i.e., to the left) consistently and significantly overshot their targets in active trials. There were no changes in accuracy of active turning to the right or passive turning in either direction. This indicates that adaptation to the rotating treadmill is expressed even when subjects have a conscious intent to turn. The positive after-effects of the rotating treadmill add to the intended active turning in the direction of the after-effect but there is no decrement in active turning in the direction opposite the after-effect.

An improved model for calculating the optical rotation of simple saccharides

A calculational model for the optical rotation (OR) at the sodium D-line of simple saccharides has been developed that eliminates deficiencies of a previous model. Conformational conclusions based on the earlier model are not affected, as established by a recalculation of the OR phi,psi-map of methyl 3-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside. The model relocates the strong long-wavelength sigma-sigma* circular dichroism (CD) component, which is mainly responsible for the NaD OR from 160 to below 130 nm, where it is now known to occur. That correction allows future modeling of CD bands of different origins that appear in the 150-190 nm region. In order to demonstrate the utility of the revised model, it was applied to calculating the OR of methyl 3-O-(alpha-L-rhamnopyranosyl)-alpha-L-rhamnopyranoside. The results provide experimental support for conformational conclusions derived from a molecular mechanics study of that molecule.

Anhydro sugar and linkage contributions to circular dichroism of agarose and carrageenan, with conformational implications

The geometry-dependent linkage contributions to the circular dichroism (CD) of agarose and carrageenan were determined by subtracting the monomeric CD from the CD of the polymers. For this purpose, the CD of methyl 3,6-anhydro-alpha-D-galactopyranoside, and of other anhydro sugars, was measured. Application of empirical quadrant rules indicates the observed CD to be that expected for the helical conformations of agarose and carrageenan as derived from diffraction data and modeling calculations. The difference in CD sign in the two polymers arises from a translocation of the beta-D-galactose O-2 atom from one quadrant to the neighboring quadrant of the C-5-O-5-C-1 ether chromophore of the preceding anhydro sugar residue, demonstrating the unusually high spatial resolution of conformational analysis that can be achieved with CD under favorable circumstances.

Experimental chiroptical verification of linkage flexibility in methyl 3-O-(alpha-d-mannopyranosyl)-alpha-d-mannopyranoside

Vacuum UV CD spectra of methyl 3-O-(alpha-D-mannopyranosyl)-alpha-D- mannopyranoside in D2O and as a cast film were obtained in the 145-200 nM region. The disaccharide solution CD per residue is nearly identical to that of the monosaccharide solution CD, and to the monosaccharide film CD. Conversely, the disaccharide film spectrum exhibits a strong positive CD linkage contribution in the 160-170 nm range, which is consistent with the known crystal conformation under the aegis of previously determined sector rules. The close similarity between the monosaccharide and disaccharide solution spectra, therefore, reflects conformational averaging in which the net linkage contribution is approximately zero. The present observation of significant solution linkage flexibility confirms previous conclusions based on optical rotation, as well as conclusions of others based on nmr data. Moreover, when combined with those earlier results, the present work demonstrates the population of at least three distinct potential energy wells on the disaccharide phi,psi potential energy surface.

Vacuum ultraviolet circular dichroism of gellan-family polymer films from water and dimethyl sulfoxide

The denaturing effect of dimethyl sulfoxide (Me2SO) on the conformation of the gellan-welan-rhamsan family of microbial polysaccharides is directly demonstrated by circular dichroism (CD). The three polysaccharides display strikingly similar CD spectra (140-210 nm) for films cast from Me2SO. The disrupting effect of Me2SO on gellan and welan conformations has previously been reported by others on the basis of light-scattering and viscosity studies. Films cast from aqueous solutions at room temperature show more-intense CD bands, both at 182 nm, as is also observed for aqueous solutions, and in the 150-175 nm region. These features correspond to the ordered helical chains found by X-ray diffraction studies of similarly prepared films.

A conformational study of agarose by vacuum UV CD

Agarose films were prepared using a variety of casting conditions, heat treatments, and solvation treatments. Films represented the high temperature sol, the room temperature gel, and a high temperature state with cross-links intact. The vacuum uv CD of the film samples varies considerably, but the similarities between the film CD and the previously reported solution CD show that dehydration per se does not affect the CD. Combining the CD results for the dried sol with the x-ray results of Foord and Atkins leads to a description of the high temperature sol in terms of locally extended chain conformations. The CD of the gel and its peculiarly high uv absorption are satisfactorily, albeit not uniquely, interpreted in terms of the double-helix model of the gel, in agreement with previous conformational studies based on chiroptical properties.

Older women who volunteer: tapping a valuable woman resource

Older women are increasing in number and are the gender who most often volunteer. Thus, an increasing pool of older women volunteers may be forthcoming. Keeping these women satisfied can serve them and the people they serve. The 119 women in this study range in age from 60 to 93, are racially diverse, and are most often low-to-middle income. For these women, volunteer satisfaction and retention relate to interaction on the job, recognition for their work, and meeting their own expectations. Methods for meeting these needs are suggested.

Making sense of usefulness: an avenue toward satisfaction in later life

Studies of later life assert that sense of usefulness impacts life satisfaction. This study determines what impacts sense of usefulness. The sample consists of 108 older adults, ages sixty through ninety, who were involved with community organizations. The research instrument was a forty-five-item questionnaire. Findings identify five correlates of sense of usefulness: continuity in respect from younger ages (p < .01), involvement with family (p < .05), involvement with a significant other (p < .01), involvement with community (p < .01), and meeting one's expectations for old age (p < .01). "Continuity in respect," "meeting one's expectations," and "sense of usefulness" combine into a scale that correlates with satisfaction in later life (p < .001). Results contribute to theoretical understanding of later life development and suggest directions for work with the aging client system.

Vacuum ultraviolet circular dichroism of fibronectin. Dominant tyrosine effects

The spectroscopic authenticity of a very intense negative band at about 183 nm reported previously from conventional circular dichroism (c.d.) studies of bovine plasma fibronectin has now been confirmed by vacuum ultraviolet c.d. measurements on two prototype spectrometers, one using a conventional light source and the other using synchrotron radiation. Closely similar spectra were obtained from both instruments, and from both solid films and solutions. The spectra show no obvious parentage in the known c.d. of the peptide backbone, but have marked similarities to the c.d. of N-acetyltyrosineamide, both in the strong band at 183 nm and in a characteristic positive band at 230 nm, It is concluded that the c.d. of fibronectin is dominated by contributions from tyrosine side-chains and that, as suggested previously, these may provide a sensitive probe for molecular organization and interactions.

A semiempirical theory of the optical activity of saccharides

A semiempirical theory of optical activity of saccharides is developed that (a) goes beyond previous empirical treatments, (b) yields calculated NaD rotations which correlate well with experimental data, and (c) accounts for a characteristic c.d. band observed for polysaccharides in the vacuum u.v. spectrum.

Vacuum ultraviolet circular dichroism of keratan sulfate

The vacuum ultraviolet CD of keratan sulfate reveals an intense negative CD band at 171 nm. Its intensity can be rationalized with a recently proposed quadrant rule in terms of the acetamido group being slightly tilted toward the hexosaminidic linkage oxygen. The same structural feature accounts for the particularly intense negative n-pi CD band near 210 nm.

Conformation of (1----6)-beta-D-glucan by vacuum-ultraviolet circular dichroism

Gelation of pustulan [(1----6)-beta-D-glucan] likely involves some chain ordering. To characterize the most probable conformation, we previously carried out energy calculations and identified the local energy minimums. Here, we analyze the (previously measured) vacuum-ultraviolet circular dichroism of pustulan by using a quadrant rule recently proposed for the 175-nm c.d. band and our earlier quantum-mechanical model for the 185-nm c.d. band. Most of the local-energy minimum conformations are shown to be inconsistent with the circular dichroism observed. Of the two distinct conformations consistent with the observed circular dichroism, one includes the global-energy minimum calculated earlier, i.e., (phi, psi, omega) = (20 degrees, -90 degrees, gt).

Solid-state 13C NMR and X-ray diffraction of dermatan sulfate

Dermatan sulfate in the solid state has been studied by 13C CP/MAS nmr and X-ray diffraction in order to establish the ring conformation of the L-iduronate moiety. The solid state nmr spectrum is similar to the solution spectrum obtained previously, indicating that a ring conformation at least approximating to 1C4 predominates in the solid state. X-ray powder diffraction data from the same sample indicate the presence of the 8-fold helix form previously observed by fiber diffraction, and interpreted in terms of a 4C1 ring form. A likely explanation of the results is that a distorted 1C4 L-iduronate ring conformation, not considered in the initial X-ray analysis, may emerge to provide a satisfactory interpretation of all available physical-chemical data.

Conformational studies of dextran [alpha-(1----6)-D-glucan]

A theoretical conformational study of dextran, a (1----6)-linked alpha-D-glucan polysaccharide, has been made to allow n explicit comparison with earlier results on pustulan, the corresponding (1----6)-linked beta-D-glucan. The nonbonded, torsional and hydrogen bond contributions to potential energy were calculated as a function of rotational angles phi, psi, and omega. The (phi, psi, omega)-space of the disaccharide and of helices contain many local energy minima with very small energy differences. A comparison of (1----6)-alpha-D-glucans with (1----6)-beta-D-glucans indicates significantly differences in conformational behavior. Specifically, our results shed light on the fact that dextran does not gel, whereas pustulan does. The difference in tendency to gel may be related to the fact that dextran has no particularly favored conformations with structural regularity whereas pustulan does.

Theoretical study of the conformations of pustulan [(1----6)-beta-D-glucan]

The total potential energy including nonbonded, torsional and hydrogen bond contributions has been computed for pustulan, a (1----6) linked beta-D-glucan polysaccharide, as a function of rotational angles phi, psi, and omega. The (phi,psi,omega)-space contains many local minima and at least three distinct deep minima. Two minima at (phi,psi,omega) = (25 degrees, 190 degrees,gg) and (phi,psi,omega) = 65 degrees, 150 degrees,gg) of almost equal energies have helical parameters (n = 5.2, h = 1.0A) and (n = 3.2, h = 1.5A), respectively. A third minimum at (phi,psi,omega) = (40 degrees, 70 degrees gt) leads to an extended zig-zag structure (n = 2.2, h = 2.2A). Energy maps obtained for gentiobiose, the disaccharide of pustulan, also reveal many local minima and the small energy differences among them indicate that gentiobiose is extremely flexible. Gentiodextrins, a family of cyclic molecules of (1----6)-beta-D-glucose residues, were also studied. Conformations free from steric hindrance were found for cyclic molecules with three to six glucose residues.

Galactofuranosyl-containing glycopeptide of Penicillium charlesii. Vacuum ultraviolet circular dichroism

The far and vacuum u.v. circular dichroism (CD) of peptidophosphogalactomannan from P. charlesii is reported to 182.5 nm in aqueous and aqueous/organic solvents, and to 150nm in films. CD of films of the peptide-free derivative is reported to 150 nm. On the basis of these data we conclude that the peptide chain is unordered, and may best be described as a hydrated coil showing some stiffness. The small observed saccharide CD may result from cancellation of contributions from the various saccharide structures present or from a lack of repeating secondary structure.

Circular dichroism conformational study of the chemotactic peptide formyl-L-methionyl-L-leucyl-L-phenylalanine

The solution circular dichroism of the chemotactic agent formyl-L-methionyl-L-leucyl-L-phenylalanine was found to be highly solvent dependent. In relatively nonpolar solvents (fluoroalcohols) the circular dichroism is that characteristic of a folded conformation. In H2SO4 the tripeptide remains intact and displays a circular dichroism typical of highly solvated and totally disordered peptides. The order-to-disorder transition can be followed by addition of water to trifluoroethanol.

Interaction of the three main components of clupeine with glycosaminoglycans

The interactions between each of the three main components of clupeine (YI, YII and Z) and the glycosaminoglycans chondroitin sulfate, heparin and hyaluronic acid were studied with circular dichroism spectroscopy. The induced dichroism is a measure of relative complex stability, which increases with the number of sulfate groups on the glycosaminoglycan. Measuring the induced dichroism as a function of mole ratio of disaccharide to arginine establishes the stoichiometry of the complexes. For a given glycosaminoglycan, the induced dichroism depends on the clupeine, increasing the order YI less than YII less than Z.

beta sheet formation by L-methionine oligopeptides

Monodispersed N- and C-protected linear homo-oligomethionines (n = 2- -7) are studied by measurements of circular dichroism in the vacuum ultraviolet region. In the solid state higher members of the series take up a beta-conformation in which both parallel and antiparallel chain arrangements are present. The strong beta-forming tendency of the methionine residue is demonstrated.