Conducting member checking within a qualitative case study on health-related behaviours in a large European city: Appraising interpretations and co-constructing findings

Although member checking is a well-established strategy for appraising credibility, there is a lack of research reporting procedures and outcomes when using this strategy. In recent years, scholars have implemented new member checking strategies along with several epistemological stances. In this work, researchers conducted member checking in three neighbourhoods with different socioeconomic status in Madrid, Spain. Attendance at member checking meetings was lower than expected. Member checking meetings were conducted in public halls within each neighbourhood and lasted approximately 2 hours. During the first hour, researchers introduced the aim of the meetings and shared summarized research findings with attendees using a slideshow. During the second hour, attendees had the opportunity to comment on any aspect of the research. Researchers used grounded theory coding strategies and a constructivist approach informed the analysis of the transcribed member checking meetings. One core category emerged, and it was named 'Co-constructing findings and side effects of the interaction between researchers and participants in member checking'. Member checking attendees contributed to co-constructing findings by means of underscore and disagreement. It is possible that these meetings might have caused side effects such as unintended comparisons between neighbourhoods and negative health-related behaviours. Attendees wondered how the findings could improve their neighbourhoods. The meetings allowed interaction between participants and researchers and resulted in appraising and co-constructing qualitative research findings. More research is needed to advance knowledge about member checking.

Predictors of engagement with remote sensing technologies for symptom measurement in Major Depressive Disorder

BACKGROUND

Remote sensing for the measurement and management of long-term conditions such as Major Depressive Disorder (MDD) is becoming more prevalent. User-engagement is essential to yield any benefits. We tested three hypotheses examining associations between clinical characteristics, perceptions of remote sensing, and objective user engagement metrics.

METHODS

The Remote Assessment of Disease and Relapse - Major Depressive Disorder (RADAR-MDD) study is a multicentre longitudinal observational cohort study in people with recurrent MDD. Participants wore a FitBit and completed app-based assessments every two weeks for a median of 18 months. Multivariable random effects regression models pooling data across timepoints were used to examine associations between variables.

RESULTS

A total of 547 participants (87.8% of the total sample) were included in the current analysis. Higher levels of anxiety were associated with lower levels of perceived technology ease of use; increased functional disability was associated with small differences in perceptions of technology usefulness and usability. Participants who reported higher system ease of use, usefulness, and acceptability subsequently completed more app-based questionnaires and tended to wear their FitBit activity tracker for longer. All effect sizes were small and unlikely to be of practical significance.

LIMITATIONS

Symptoms of depression, anxiety, functional disability, and perceptions of system usability are measured at the same time. These therefore represent cross-sectional associations rather than predictions of future perceptions.

CONCLUSIONS

These findings suggest that perceived usability and actual use of remote measurement technologies in people with MDD are robust across differences in severity of depression, anxiety, and functional impairment.

Remote Assessment of Disease and Relapse in Major Depressive Disorder (RADAR-MDD): Recruitment, retention, and data availability in a longitudinal remote measurement study

Introduction

Major Depressive Disorder (MDD) is prevalent, often chronic, and requires ongoing monitoring of symptoms to track response to treatment and identify early indicators of relapse. Remote Measurement Technologies (RMT) provide an exciting opportunity to transform the measurement and management of MDD, via data collected from inbuilt smartphone sensors and wearable devices alongside app-based questionnaires and tasks.

Objectives

To describe the amount of data collected during a multimodal longitudinal RMT study, in an MDD population.

Methods

RADAR-MDD is a multi-centre, prospective observational cohort study. People with a history of MDD were provided with a wrist-worn wearable, and several apps designed to: a) collect data from smartphone sensors; and b) deliver questionnaires, speech tasks and cognitive assessments and followed-up for a maximum of 2 years.

Results

A total of 623 individuals with a history of MDD were enrolled in the study with 80% completion rates for primary outcome assessments across all timepoints. 79.8% of people participated for the maximum amount of time available and 20.2% withdrew prematurely. Data availability across all RMT data types varied depending on the source of data and the participant-burden for each data type. We found no evidence of an association between the severity of depression symptoms at baseline and the availability of data. 110 participants had > 50% data available across all data types, and thus able to contribute to multiparametric analyses.

Conclusions

RADAR-MDD is the largest multimodal RMT study in the field of mental health. Here, we have shown that collecting RMT data from a clinical population is feasible.

Disclosure

No significant relationships.

Changes in perceptions of the alcohol environment among participants in a Photovoice project conducted in two districts with different socio-economic status

Perceptions of the alcohol environment may influence alcohol consumption patterns. The purpose of this study was to describe changes in perceptions of the urban alcohol environment as experienced by residents of two districts with different socio-economic status after taking part in a Photovoice study. The study was conducted in Madrid, Spain, in a district with a high socio-economic status (HSES) and another district with a low socio-economic status (LSES). A Photovoice project was conducted with 26 participants divided into four groups based on sex and district. Groups met over five sessions in which they discussed photographs taken by the participants themselves on the subject of alcohol in their neighbourhood. A qualitative, descriptive and thematic analysis of participants' discourses was performed to explore changes in their perceptions of the alcohol environment over the project sessions. Changes in perceptions of the alcohol environment were observed in all groups over the project. The process of change varied by districts' socio-economic characteristics and gender. Greater changes in perceptions of the alcohol environment were observed in HSES, especially among women, as the participants had a much more positive initial view of their alcohol environment. In LSES, participants showed a more critical perception of the alcohol environment from the beginning of the study, and this broadened and intensified over the course of the sessions. Changes in perceptions also varied by thematic categories, including some categories that were discussed from the start (e.g. socialising and alcohol consumption) and categories that only emerged in later sessions (e.g. alcohol advertising). Involvement in a Photovoice project has favoured a shift in the participant's perceptions of their alcohol environment towards more critical positions, widening their scope of perceived elements and raising their awareness of specific problems, such as alcohol advertising and social role of alcohol consumption in relation to alcohol exposure.

Residents perceptions of the alcohol environment: A participatory photovoice project in two districts with different socio-economic status in a large city

The purpose of this study was to present the alcohol environment as perceived by its residents in two districts of Madrid using the Photovoice participatory methodology. Secondly, we compared the results according to the socio-economic status of the districts. The study was conducted in the city of Madrid, Spain, in two districts with different socio-economic status. A total of 26 people participated, who took and discussed photographs about their alcohol environment. They grouped them into 33 final categories, such as the socialising role of alcohol or the alcohol advertising. Co-authors further grouped participants final categories into seven general areas. The participants in the Photovoice project have helped to deepen the understanding of the alcohol urban environment. These results may help to design more effective policies to prevent hazardous alcohol consumption.

Urban environment and dietary behaviours as perceived by residents living in socioeconomically diverse neighbourhoods: A qualitative study in a Mediterranean context

Scholars have determined that low socioeconomic status (SES) is associated with unhealthy dietary behaviours and that local food environments shape food inequality. Less is known about how residents' perceptions of their food environment affect their dietary behaviours. We conducted 37 semistructured interviews and 29 focus groups in three socioeconomically distinct neighbourhoods in Madrid. We identified the following main categories related to social and physical food environments: (a) perceptions of healthy and unhealthy dietary behaviours, (b) children's relationships with food, (c) precariousness and (d) residential food retailer types. Older adults were perceived as healthier consumers, whereas younger people were identified as fast-food consumers. In the low- and middle-SES neighbourhoods, residents saw home-cooked legume-based stews as healthy food. In the high-SES neighbourhood, television cooking programs were highlighted as a positive influence. In the low- and middle-SES neighbourhoods, grandparents played an essential role in the transmission of healthy eating habits to their grandchildren. In the high-SES neighbourhood, children's diets at home were determined by school menus. In the low- and middle-SES neighbourhoods, participants talked about a black market where food could be purchased. Food retailers with low-quality foods were also highlighted. In all neighbourhoods, residents missed traditional food stores, and in the low- and middle-SES neighbourhoods, immigrant-run food stores were not well accepted. Our study presents the concepts shaping how neighbourhood SES differences affect dietary behaviours according to residents of a large Mediterranean city.

Social Norms Influencing the Local Food Environment as Perceived by Residents and Food Traders: The Heart Healthy Hoods Project

Exploring subjective elements of the food environment remains key to understand why and how residents purchase food. Our aim was to explore and describe the social norms relating to the local food environment and food purchasing behaviors, as perceived by residents and food traders in Madrid, Spain. This qualitative study took place in a middle socioeconomic status neighborhood of Madrid between January 2015 and May 2016. We conducted 35 semi-structured interviews. We used stratified purposive sampling to recruit residents, neighborhood workers (N = 20) and food traders (N = 15) representing different levels of involvement with food purchasing behaviors. We analyzed these data using an interpretative phenomenological analysis approach. Participants highlighted social aspects of the food environment in relation to food purchasing behaviors. First, interpersonal and relational food environment elements were emphasized, including trust and tradition. Participants also identified generational demographic trends in relation to changes in the way residents purchased food: the new pace of life and the lack of time to buy fresh food and to cook at home. All these elements were influenced by the economic crisis. Food environment interventions aiming to improve food purchasing behaviors and residents' diets should consider intermediate social aspects of the food environment like trust and tradition and the fast pace of life of younger generations.

Associated Factors for Health Quality of Life in Moroccan Women With Breast Cancers

Background: Breast cancer is the most common cancer among women. Breast cancer is ranked the first female cancer (33.4%) in Morocco; and more than 60% cases are diagnosed at stage III or IV. During the last decade, health-related quality of life (HRQOL) has become an important part of breast cancer treatment. Aim: The objective of this study is to describe self- reported HRQOL in patients with breast cancer and to investigate its associations with socio-demographic and clinical variables. Methods: A prospective study was carried out in the main oncology centers in Morocco. Quality of life was measured using the Moroccan Arabic version of the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire C 30 (EORTC QLQ C30) and Breast Cancer-Specific Quality of Life Questionnaire (EORTC QLQ-BR23). Statistical data analyses were performed using descriptive statistics and multivariate analyses. Results: A total of 1463 subjects were included in the study. The subjects' mean age was 55.6 (SD. 11.2) years, 70% were married. The majority of the subjects had stage II (45.9%) and the few cases had stage IV (12.9%). Participants had a mean score for global health of 68.5. Among functional scales, social functioning scored the highest (mean 86.2, SD = 22.7). The most distressing symptom on the symptom scales was financial difficulties (mean 63.2, SD = 38.2). Using the disease-specific tool, it was found that future perspective scored the lowest (mean 40.5, SD = 37.3). On the symptom scale, arm symptoms scored the highest (mean 23.6, SD = 21.6). Significant mean differences were noted for many functional and symptom scales. Conclusion: Our results emphasize that the general HRQOL of the studied women is fairer than that of the corresponding population in other countries. This study provided baseline information on the quality of life of a large sample of Moroccan women diagnosed with breast cancer.

Changing Neighborhoods and Residents' Health Perceptions: The Heart Healthy Hoods Qualitative Study

Cities, and therefore neighborhoods, are under constant change. Neighborhood changes may affect residents’ health in multiple ways. The Heart Healthy Hoods (HHH) project studies the association between neighborhood and residents’ health. Focusing on a middle–low-socioeconomic neighborhood in Madrid (Spain), our aim was to describe qualitatively its residents’ perceptions on the urban changes and their impacts on health. We designed a qualitative study using 16 semi-structured interviews including adult residents and professionals living or working in the area. Firstly, we described the perceived main social and neighborhood changes. Secondly, we studied how these neighborhood changes connected to residents’ health perceptions. Perceived major social changes were new demographic composition, new socio–cultural values and economic changes. Residents’ negative health perceptions were the reduction of social relationships, increase of stress and labor precariousness. Positive health perceptions were the creation of supportive links, assimilation of self-care activities and the change in traditional roles. Neighborhood changes yielded both negative and positive effects on residents’ health. These effects would be the result of the interrelation of different elements such as the existence or absence of social ties, family responsibilities, time availability, economic resources and access and awareness to health-promoting programs. These qualitative research results provide important insight into crafting urban health policies that may ultimately improve health outcomes in communities undergoing change.

Photovoice and empowerment: evaluating the transformative potential of a participatory action research project

BACKGROUND

Photovoice is a visual research methodology with the intention to foster social change. Photovoice has been used to investigate change in empowerment in vulnerable communities, However, the individual experience of participants involved in Photovoice projects is seldom scrutinized. Our aim was to explore and describe the individual experiences of the female individuals who participated in a previous Photovoice project. We analyzed a change in the women's empowerment in terms of: 1) gain in knowledge and skills, 2) change in self-perception, and 3) access to and use of resources.

METHODS

This qualitative study took place in the low-income District of Villaverde (Madrid, Spain), from January-June 2016. We conducted 10 semi-structured interviews with the female residents who had participated in the previous Photovoice project. We also collected field notes. We analyzed these data through a direct qualitative content analysis. The three outlined dimensions of empowerment provided guidance for the analysis of the results.

RESULTS

We found positive changes in the three dimensions of empowerment: 1) participants acquired new knowledge and developed critical awareness of their community; 2) the social recognition participants received transformed their self-perception; and 3) the project allowed them to expand their social networks and to build new links with different actors (research partners, local decision makers, media and the wider public).

CONCLUSIONS

Photovoice projects entail the opportunity for empowering participants. Future research using Photovoice should assess the influence it has on participants' empowerment changes and how to sustain these individual and social changes.

ALBIRA: a small animal PET∕SPECT∕CT imaging system

PURPOSE

The authors have developed a trimodal PET∕SPECT∕CT scanner for small animal imaging. The gamma ray subsystems are based on monolithic crystals coupled to multianode photomultiplier tubes (MA-PMTs), while computed tomography (CT) comprises a commercially available microfocus x-ray tube and a CsI scintillator 2D pixelated flat panel x-ray detector. In this study the authors will report on the design and performance evaluation of the multimodal system.

METHODS

X-ray transmission measurements are performed based on cone-beam geometry. Individual projections were acquired by rotating the x-ray tube and the 2D flat panel detector, thus making possible a transaxial field of view (FOV) of roughly 80 mm in diameter and an axial FOV of 65 mm for the CT system. The single photon emission computed tomography (SPECT) component has a dual head detector geometry mounted on a rotating gantry. The distance between the SPECT module detectors can be varied in order to optimize specific user requirements, including variable FOV. The positron emission tomography (PET) system is made up of eight compact modules forming an octagon with an axial FOV of 40 mm and a transaxial FOV of 80 mm in diameter. The main CT image quality parameters (spatial resolution and uniformity) have been determined. In the case of the SPECT, the tomographic spatial resolution and system sensitivity have been evaluated with a (99m)Tc solution using single-pinhole and multi-pinhole collimators. PET and SPECT images were reconstructed using three-dimensional (3D) maximum likelihood and ordered subset expectation maximization (MLEM and OSEM) algorithms developed by the authors, whereas the CT images were obtained using a 3D based FBP algorithm.

RESULTS

CT spatial resolution was 85 μm while a uniformity of 2.7% was obtained for a water filled phantom at 45 kV. The SPECT spatial resolution was better than 0.8 mm measured with a Derenzo-like phantom for a FOV of 20 mm using a 1-mm pinhole aperture collimator. The full width at half-maximum PET radial spatial resolution at the center of the field of view was 1.55 mm. The SPECT system sensitivity for a FOV of 20 mm and 15% energy window was 700 cps∕MBq (7.8 × 10(-2)%) using a multi-pinhole equipped with five apertures 1 mm in diameter, whereas the PET absolute sensitivity was 2% for a 350-650 keV energy window and a 5 ns timing window. Several animal images are also presented.

CONCLUSIONS

The new small animal PET∕SPECT∕CT proposed here exhibits high performance, producing high-quality images suitable for studies with small animals. Monolithic design for PET and SPECT scintillator crystals reduces cost and complexity without significant performance degradation.

Expectation maximization (EM) algorithms using polar symmetries for computed tomography (CT) image reconstruction

We suggest a symmetric-polar pixellation scheme which makes possible a reduction of the computational cost for expectation maximization (EM) iterative algorithms. The proposed symmetric-polar pixellation allows us to deal with 3D images as a whole problem without dividing the 3D problem into 2D slices approach. Performance evaluation of each approach in terms of stability and image quality is presented. Exhaustive comparisons between all approaches were conducted in a 2D based image reconstruction model. From these 2D approaches, that showing the best performances were finally implemented and evaluated in a 3D based image reconstruction model. Comparison to 3D images reconstructed with FBP is also presented. Although the algorithm is presented in the context of computed tomography (CT) image reconstruction, it can be applied to any other tomographic technique as well, due to the fact that the only requirement is a scanning geometry involving measurements of an object under different projection angles. Real data have been acquired with a small animal (CT) scanner to verify the proposed mathematical description of the CT system.

Towards an operational system for oil-spill forecast over Spanish waters: initial developments and implementation test

The ESEOO Project, launched after the Prestige crisis, has boosted operational oceanography capacities in Spain, creating new operational oceanographic services and increasing synergies between these new operational tools and already existing systems. In consequence, the present preparedness to face an oil-spill crisis is enhanced, significantly improving the operational response regarding ocean, meteorological and oil-spill monitoring and forecasting. A key aspect of this progress has been the agreement between the scientific community and the Spanish Search and Rescue Institution (SASEMAR), significantly favoured within the ESEOO framework. Important achievements of this collaboration are: (1) the design of protocols that at the crisis time provide operational state-of-the-art information, derived from both forecasting and observing systems; (2) the establishment, in case of oil-spill crisis, of a new specialized unit, named USyP, to monitor and forecast the marine oceanographic situation, providing the required met-ocean and oil-spill information for the crisis managers. The oil-spill crisis scenario simulated during the international search and rescue Exercise "Gijón-2006", organized by SASEMAR, represented an excellent opportunity to test the capabilities and the effectiveness of this USyP unit, as well as the protocols established to analyze and transfer information. The results presented in this work illustrate the effectiveness of the operational approach, and constitute an encouraging and improved base to face oil-spill crisis.

Limits for the central production of Theta+ and Xi(--)pentaquarks in 920-GeV pA collisions

We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).

Somatic embryogenesis and plant regeneration from leaves of Ulmus minor Mill

Somatic embryogenesis from mature elm ( Ulmus minor Mill.) in vitro-cloned material is possible. Embryogenic callus was obtained from leaves inoculated on two different MS-based media-one supplemented with 2.3 microM 2,4-dichlorophenoxyacetic acid (I2) and the other supplemented with 1.1 microM kinetin (I6). However, only leaves cultured on medium I6 produced somatic embryos, at the globular stage, when embryogenic callus was maintained in induction media. When embryogenic callus from medium I6 was transferred to basal medium, somatic embryos with green cotyledons were obtained. An average of 35.9% of these embryos converted easily into normal plants in conversion medium with 1% sucrose. Acclimatisation reached 39.7%, and this was not significantly different from a control group consisting of plants propagated by axillary buds. No morphological differences were observed between plants derived from somatic embryos and control plants. Also, no differences in ploidy were detected between the somatic embryo-derived plants and the mother plants.

Using the Web to aid biochemists and microbiologists: an example of computer-based learning using PCR as an example

The aim of this study was two-fold: to make available to the medical community a fast, efficient tool for troubleshooting PCR problems, and to demonstrate that hypermedia allow one to approach this kind of problem in a new, more useful way. The Web provides access to an enormous amount of information in the medical area, and in particular enables troubleshooting of new techniques in the medical laboratory. Currently it is possible to find textual information but it is not always easy to find hypermedia information. In many cases authors change only the means of dissemination of a book or paper to the Web, but do not adapt the information to the features of this new medium. The prototype of our hypermedia application was developed using Director and Flash programs (Macromedia), the application was developed from a decision tree built as a result of information compiled from expert PCR users and the existing literature. It was implemented on a website using Dreamweaver (Macromedia). The usefulness and possibilities of this application have been tested with physicians, medical laboratory technicians, and health science students, and have been proven to be more effective than traditional methods, both in education processes and in helping researchers and medical laboratory technicians in their daily work. The advance and popularization of the Internet in the medical profession requires information on the Web to adapt to the advantages offered by hypermedia. This new step must be taken, and the Web must offer medical users not only a different medium of information distribution but also a new way of handling and obtaining information.

Hydrogastric sonography in the preoperative staging of gastric cancer

PURPOSE

Depth of wall invasion is the main prognostic factor in gastric cancer. We studied the utility of hydrogastric sonography in the evaluation of transmural infiltration by gastric cancer.

METHODS

Thirty-seven patients with gastric adenocarcinoma were examined before surgery with a 5-MHz probe after the ingestion of 100-400 ml of water (mean, 330 ml). Sonographic results were compared with pathologic classifications obtained after surgery.

RESULTS

Of the 37 tumors, 15 were found at surgery to be in the antrum, 10 were in the gastric body, 5 were proximal, and 7 were diffuse. After surgery, tumors were classified as follows: 2 (5%) T1, 4 (11%) T2, 15 (41%) T3, and 16 (43%) T4. Hydrogastric sonography correctly classified 30 (81%) of the 37 tumors. Sonography was correct for 2 (100%) of the 2 T1 tumors, 2 (50%) of the 4 T2 tumors, 13 (87%) of the 15 T3 tumors, and 13 (81%) of the 16 T4 tumors. Five sonographic errors were due to understaging and 4 to overstaging. With regard to tumor site, sonographic results were correct for 4 (57%) of the 7 diffuse tumors, 3 (60%) of the 5 proximal tumors, 9 (90%) of the 10 gastric body tumors, and 14 (93%) of the 15 antral tumors.

CONCLUSIONS

Hydrogastric sonography is useful for preoperative evaluation of transmural infiltration by gastric cancers, particularly tumors in the antrum or gastric body.

[Usefulness of abdominal echography in the diagnosis of active Crohn's disease]

OBJECTIVE

The aim of this study was to evaluate the relevance of the ultrasonography in assessing activity in a series of patients with Crohn's disease.

PATIENTS AND METHODS

A series of 24 patients with active (Crohn's disease activity index > 150) ileal or ileocolonic Crohn disease underwent abdominal ultrasonography.

RESULTS

There was a significant correlation between bowel wall thickening and the Crohn's disease activity index: the higher the bowel wall thickening was the higher were the values of Crohn's disease activity index. Two or more ultrasound studies were performed in 10 patients with bowel wall > 4 mm during treatment, and a progressive normalization of bowel wall size was observed with new thickening when recurrence occurred.

CONCLUSIONS

A bowel wall thickening (> or = 4 mm) was found in patients with active Crohn's disease. A patient with bowel wall thickness > 6 mm should make us suspect the presence of stenosis. Abdominal ultrasonography is an accurate method in the first assessment of Crohn's disease because its high correlation with the Crohn's disease activity index.

Bilirubinate granules: main pathologic bile component in patients with idiopathic acute pancreatitis

OBJECTIVE

The aim of this study was to evaluate the main pathologic component of bile obtained by biliary drainage in patients with acute idiopathic pancreatitis and therapeutic implications.

METHOD

Eighteen patients diagnosed with idiopathic acute pancreatitis underwent biliary drainage. Microscopic evaluation of bile was performed and pathologic components were classified in cholesterol microcrystals, bilirubinate granules, and calcium microspherolites.

RESULTS

Five patients showed no abnormalities. In 11 patients, bilirubinate granules were found, cholesterol microcrystals in two, and Giardia lamblia in two.

CONCLUSION

Bilirubinate granules are the main pathologic component of bile in patients with acute idiopathic pancreatitis. Cholecystectomy is the preferred therapeutic approach.

Studies on the modification of Escherichia coli ribosomal protein L7/L12 by succinic anhydride

Lysine modification by increasing quantities of succinic anhydride in the Escherichia coli ribosomal protein L7/L12 produces loss of its ability in reconstitution of elongation-factor-G-dependent GTP hydrolysis and polyphenylalanine synthesis activities, showing lower antigenicity and loss of antigenic determinants.

Acidic ribosomal proteins from eukaryotic cells. Effect on ribosomal functions

Precipitation of Saccharomyces cerevisiae ribosomes by ethanol under experimental conditions that do not release the ribosomal proteins can affect the activity of the particles. In the presence of 0.4 M NH4Cl and 50% ethanol only the most acidic proteins from yeast and rat liver ribosomes are released. At 1 M NH4Cl two more non-acidic proteins are lost from the ribosomes. The release of the acidic proteins causes a small inactivation of the polymerizing activity of the particles, additional to that caused by the precipitation itself. The elongation-factor-2-dependent GTP hydrolysis of the ribosomes is, however, more affected by the loss of acidic proteins. These proteins can stimulate the GTPase but not the polymerising activity when added back to the treated particles. Eukaryotic proteins cannot be substituted for bacterial acidic proteins L7 and L12. We have not detected immunological cross-reaction between acidic proteins from Escherichia coli and those from yeast, Artemia salina and rat liver or between acidic proteins from these eukaryotic ribosomes among themselves.

Peptidyl transferase of bacterial ribosome: resistance to proteinase K

70-S ribosomes and 50-S ribosomal subunits from Escherichia coli D10 were treated with proteinase K for increasing periods of time. Peptidyl transferase activity and sparsomycin-induced binding of (U)C-A-C-C-A-[3H]Leu-Ac were tested in the treated particles, the binding of the substrate being more sensitive to the protease than peptide bond formation. Comparison of the amounts of proteins present in the treated particles with the residual activity indicates that only proteins L3 and L14 are released at a similar rate to that at which peptidyl transferase activity is lost. Proteins related to this ribosomal activity by other techniques are lost at a faster rate than the activity itself. In addition, the results indicate that sparsomycin stimulates the binding of the substrate by a different mechanism from that which inhibits peptide bond formation.