Studies of solute self-association by sedimentation equilibrium: allowance for effects of thermodynamic non-ideality beyond the consequences of nearest-neighbor interactions

A sedimentation equilibrium study of a-chymotrypsin self-association in acetate-chloride buffer, pH 4.1 I 0.05, has been used to illustrate determination of a dimerization constant under conditions where thermodynamic non-ideality is manifested beyond the consequences of nearest-neighbor interactions. Because the expressions for the experimentally determinable interaction parameters comprise a mixture of equilibrium constant and excluded volume terms, the assignment of reasonable magnitudes to the relevant virial coefficients describing non-associative cluster formation is essential for the evaluation of a reliable estimate of the dimerization constant. Determination of these excluded volume parameters by numerical integration over the potential-of-mean-force is shown to be preferable to their calculation by approximate analytical solutions of the integral for this relatively small enzyme monomer with high net charge (+ 10) under conditions of low ionic strength (0.05 M). (C) 2001 Elsevier Science B.V. All rights reserved.

Ultracentrifugal studies of the effect of molecular crowding by trimethylamine N-oxide on the self-association of muscle glycogen phosphorylase b

The suitability of sedimentation equilibrium for characterizing the self-association of muscle glycogen phosphorylase b has been reappraised. Whereas sedimentation equilibrium distributions for phosphorylase b in 40 mM Hepes buffer (pH 6.8) supplemented with 1 mM AMP signify a lack of chemical equilibrium attainment, those in buffer supplemented additionally with potassium sulfate conform with the requirements of a dimerizing system in chemical as we:ll as sedimentation equilibrium. Because the rate of attainment of chemical equilibrium under the former conditions is sufficiently slow to allow resolution of the dimeric and tetrameric enzyme species by sedimentation velocity, this procedure has been used to examine the effects of thermodynamic nonideality arising from molecular crowding try trimethylamine N-oxide on the self-association behaviour of phosphorylase b. In those terms the marginally enhanced extent of phosphorylase b self-association observed in the presence of high concentrations of the cosolute is taken to imply that the effects of thermodynamic nonideality on the dimer-tetramer equilibrium are being countered by those displacing the T reversible arrow R isomerization equilibrium for dimer towards the smaller, nonassociating T state. Because the R state is the enzymically active form, an inhibitory effect is the predicted consequence of molecular crowding by high concentrations of unrelated solutes. Thermodynamic nonideality thus provides an alternative explanation for the inhibitory effects of high concentrations of glycerol, sucrose and ethylene glycol on phosphorylase b activity, phenomena that have been attributed to extremely weak interaction of these cryoprotectants with the T state of the enzyme.

The validity of self-reported energy intake as determined using the doubly labelled water technique

In the 1980s the development of the doubly labelled water (DLW) technique made it possible to determine the validity of dietary assessment methods using external, independent markers of intake in free-living populations. Since then, the accuracy of self-reported energy intake (EI) has been questioned on a number of occasions as under-reporting has been found to be prevalent in many different populations. This paper is a review of investigations using the DLW technique in conjunction with self-reported EI measures in groups including adults, children and adolescents, obese persons, athletes, military personnel and trekking explorers. In studies where a person other than the subject is responsible for recording dietary intake, such as parents of young children, EI generally corresponds to DLW determined energy expenditure. However, in instances where the subjects themselves report their intake, EI is generally under-reported when compared with energy expenditure. It was originally believed that this phenomenon of under-reporting was linked to increased adiposity and body size, however, it is now apparent that other factors, such as dietary restraint and socio-economic status, are also involved. This paper therefore aims to present a more comprehensive picture of under-reporting by tying in the findings of many DLW studies with other studies focusing particularly on the characteristics and mechanisms for under-reporting. Awareness of these characteristics and mechanisms will enable researchers to obtain more accurate self-reports of EI using all dietary recording techniques.

Coffee and alcohol consumption and the risk of pancreatic cancer in two prospective United States cohorts

Although most prospective cohort studies do not support an association between coffee consumption and pancreatic cancer, the findings for alcohol are inconsistent. Recently, a large prospective cohort study of women reported statistically significant elevations in risk of pancreatic cancer for both coffee and alcoholic beverage consumption. We obtained data on coffee, alcohol, and other dietary factors using semiquantitative food frequency questionnaires administered at baseline (1986 in the Health Professionals Follow-Up Study and 1980 in the Nurses’ Health Study) and in subsequent follow-up questionnaires. Data on other risk factors for pancreatic cancer, including cigarette smoking, were also available. Individuals with a history of cancer at study initiation were excluded from all of the analyses. During the 1,907,222 person-years of follow-up, 288 incident cases of pancreatic cancer were diagnosed. The data were analyzed separately for each cohort, and results were pooled to compute overall relative risks (RR). Neither coffee nor alcohol intakes were associated with an increased risk of pancreatic cancer in either cohort or after pooling the results (pooled RR, 0.62; 95% confidence interval, 0.27–1.43, for >3 cups of coffee/day versus none; and pooled RR, 1.00; 95% confidence interval, 0.57–1.76, for >=30 grams of alcohol/day versus none). The associations did not change with analyses examining different latency periods for coffee and alcohol. Similarly, no statistically significant associations were observed for intakes of tea, decaffeinated coffee, total caffeine, or alcoholic beverages. Data from these two large cohorts do not support any overall association between coffee intake or alcohol intake and risk of pancreatic cancer.

Communication and health beliefs - Mass and interpersonal influences on perceptions of risk to self and others

This study investigated the impact of media coverage of a health issue (skin cancer) on judgements of risk to self and others and the role of related communication processes. Consistent with predictions derived from the impersonal impact hypothesis, the effects of mass communication were more evident in perceptions of risk to others rather than in perceptions of personal risk. Perceptions of personal risk were more strongly correlated with interpersonal communication. However, as suggested by media system dependency theory, the relationship between mass communication and beliefs was complex. The impact of mass communication on both personal and impersonal perceptions was bound to be moderated by self-reported dependence on mass mediated information. The effect of this two-way interaction 071 perceptions of personal risk was partially mediated through interpersonal communication. Results point to the interdependence of mass and interpersonal communication as sources of social influence and the role of media dependency in shaping media impact.

Assessing self- and peer-assessment: The students' views

Self- and peer-assessment are being used increasingly in higher education, to help assign grades to students' work and to help students to learn more effectively. However, in spite of this trend there is little in the published literature on how students view these methods. In this paper we present an analysis of the views of a large number of students (N = 233) who had just experienced self- and peer-feedback as part of one of their subjects. It is a rarely questioned commonplace in the literature that in order to gain benefit from peer and self-assessment schemes students first need training in the specific scheme being used; ideally they will play a role in devising the scheme. The intervention reported here, which involved a large (N = 233) group of students, included no such measures. The results show that students felt, nonetheless, that they benefited from the intervention. The results also present prima facie evidence that training or other measures to further involve the students in the peer and self-assessment scheme might be beneficial. Our analysis of students' views revealed eight general dimensions under which are grouped twenty higher order themes. The results both support and extend previous research and give a more detailed picture than previously available. The general dimensions found were: Difficult; Gained Better Understanding of Marking; Discomfort; Productive (including learning benefits and improved work); Problems with Implementation; Read Others' Work; Develop Empathy (with assessing staff); and, Motivation (especially motivation to impress peers). The practical implications of these findings are discussed.

Effects of alcohol consumption on indices of iron stores and of iron stores on alcohol intake markers

Background: Alcohol increases body iron stores. Alcohol and iron may increase oxidative stress and the risk of alcohol-related liver disease. The relationship between low or safe levels of alcohol use and indices of body iron stores, and the factors that affect the alcohol-iron relationship, have not been fully characterized. Other aspects of the biological response to alcohol use have been reported to depend on iron status. Methods: We have measured serum iron, transferrin, and ferritin as indices of iron stores in 3375 adult twin subjects recruited through the Australian Twin Registry. Information on alcohol use and dependence and smoking was obtained from questionnaires and interviews. Results: Serum iron and ferritin increased progressively across classes of alcohol intake. The effects of beer consumption were greater than those of wine or spirits. Ferritin concentration was significantly higher in subjects who had ever been alcohol dependent. There was no evidence of interactions between HFE genotype or body mass index and alcohol. Alcohol intake-adjusted carbohydrate-deficient transferrin was increased in women in the lowest quartile of ferritin results, whereas adjusted gamma -glutamyltransferase, aspartate aminotransferase, and alanine aminotransferase values were increased in subjects with high ferritin. Conclusions: Alcohol intake at low level increases ferritin and, by inference, body iron stores. This may be either beneficial or harmful, depending on circumstances. The response of biological markers of alcohol intake can be affected by body iron stores; this has implications for test sensitivity and specificity and for variation in biological responses to alcohol use.

The validity of an Australian modification of the AUDIT questionnaire

The Alcohol Use Disorders Identification Test (AUDIT) has been used widely and is reported to be superior to conventional questionnaires in detection of current hazardous and harmful alcohol use. We assessed the validity of an Australian modification of the AUDIT (the AusAUDIT), which has been employed widely in Australian and New Zealand early intervention programmes. We used a cross-sectional study of 370 subjects from the follow-up phase of a randomized controlled trial of early intervention to reduce hazardous alcohol consumption. Scores on the AusAUDIT were compared against 12-month ICD-10 diagnoses of harmful alcohol use and dependence, as determined by the Composite International Diagnostic Interview, and against self-report of alcohol consumption exceeding Australian National Health and Medical Research Council (NH&MRC) recommended limits. AusAUDIT had good internal consistency and discriminated significantly between persons meeting criteria for ICD-10 alcohol use disorders, and drinkers who did not. At currently recommended cut-off scores, AusAUDIT detected more than 85% of people meeting criteria for ICD-10 alcohol use disorders, or drinking over NH&MRC recommended limits, but its specificity was limited (29% in men, and 58% in women for drinking over NH&MRC limits). No subset of questions performed as well as the full AusAUDIT in detection of drinking problems, but the alcohol consumption items provided a reasonable screen for drinking over NH&MRC limits. We conclude that AusAUDIT is effective in detecting problematic drinking, but positive cases should be confirmed by clinical assessment. The findings illustrate the need for validation of questionnaire modifications, and the difficulty in increasing test sensitivity without reducing specificity.

Self-reported calcium intake and bone mineral content in children and adolescents

Objective: We examined the relationship between self-reported calcium (Cal intake and bone mineral content (BMC) in children and adolescents. We hypothesized that an expression of Ca adjusted for energy intake (El), i.e., Ca density, would be a better predictor of BMC than unadjusted Ca because of underreporting of EI. Methods: Data were obtained on dietary intakes (repeated 24-hour recalls) and BMC (by DEXA) in a cross-section of 227 children aged 8 to 17 years. Bivariate and multivariate analyses were used to examine die relationship between Ca, Ca density, and the dependent variables total body BMC and lumbar spine BMC. Covariates included were height, weight, bone area, maturity age, activity score and El. Results: Reported El compared to estimated basal metabolic rate suggested underreporting of El. Total body and lumbar spine BMC were significantly associated with El, but not Ca or Ca density, in bivariate analyses. After controlling for size and maturity, multiple linear regression analysis revealed unadjusted Ca to be a predictor of BMC in males in the total body (p = 0.08) and lumbar spine (p = 0.01). Unadjusted Ca was not a predictor of BMC at either site in females. Ca density was not a better predictor of BMC at either site in males or females. Conclusions: The relationship observed in male adolescents in this study between Ca intake and BMC is similar to that seen in clinical trials. Ca density did not enable us to see a relationship between Ca intake and BMC in females, which may reflect systematic reporting errors or that diet is not a limiting factor in this group of healthy adolescents.