93,030 research outputs found
Dimeric pig heart succinate-coenzyme A transferase uses only one subunit to support catalysis
No full textPig heart succinate-coenzyme A transferase (succinyl-coenzyme A: 3-oxoacid coenzyme A transferase; E. C. 2.8.3.5.), a dimeric enzyme purified by affinity chromatography on Procion Blue MX-2G Sepharose, reacts with acetoacetyl-coenzyme A to form a covalent enzyme-coenzyme A thiolester intermediate in which the active site glutamate (E344) of both subunits each forms thiolester links with coenzyme A. Reaction of this dimeric enzyme-coenzyme A species with sodium borohydride leads to inactivation of the enzyme and reduction of the thiolester on both subunits to the corresponding enzyme alcohol, as judged by electrospray mass spectrometry. Reaction of the dimeric enzyme-coenzyme A intermediate with either succinate or acetoacetate, however, results in only one-half of the coenzyme A being transferred to the acceptor carboxylate to form either succinyl-coenzyme A or acetoacetyl-coenzyme A. Reaction of this latter enzyme species with borohydride caused no loss of enzyme activity despite the reduction of the remaining half of the enzyme-coenzyme A thiolester to the enzyme alcohol. That this catalytic asymmetry existed between subunits within the same enzyme dimer was demonstrated by showing that the enzyme species, created by successive reaction with acetoacetyl-coenzyme A and succinate, bound to Blue MX-2G Sepharose through the remaining available active site and could be eluted as a single chromatographic species by succinyl-coenzyme A. It is concluded that while both of the subunits of the succinate-coenzyme A transferase dimer are able to form enzyme-coenzyme A thiolester intermediates, only one subunit is competent to transfer the coenzyme A moiety to a carboxylic acid acceptor to form the new acyl-coenzyme A product. The possible structural basis for this catalytic asymmetry and its mechanistic implications are discussed
X-ray structure of a putative reaction intermediate of 5-aminolaevulinic acid dehydratase
No full textThe X-ray structure of yeast 5-aminolaevulinic acid dehydratase, in which the catalytic site of the enzyme is complexed with a putative cyclic intermediate composed of both substrate moieties, has been solved at 0.16 nm (1.6 Å) resolution. The cyclic intermediate is bound covalently to Lys(263) with the amino group of the aminomethyl side chain ligated to the active-site zinc ion in a position normally occupied by a catalytic hydroxide ion. The cyclic intermediate is catalytically competent, as shown by its turnover in the presence of added substrate to form porphobilinogen. The findings, combined with those of previous studies, are consistent with a catalytic mechanism in which the C–C bond linking both substrates in the intermediate is formed before the C–N bond
5-Aminolaevulinic acid dehydratase: metals, mutants and mechanism
No full text5-Aminolaevulinic acid dehydratase catalyses the formation of porphobilinogen from two molecules of 5-aminolaevulinic acid. The studies described highlight the importance of a bivalent metal ion and two active-site lysine residues for the functioning of 5-aminolaevulinic acid dehydratase. Dehydratases fall into two main categories: zinc-dependent enzymes and magnesium-dependent enzymes. Mutations that introduced zinc-binding ligands into a magnesium-dependent enzyme conferred an absolute requirement for zinc. Mutagenesis of lysine residues 247 and 195 in the Escherichia coli enzyme lead to dramatic effects on enzyme activity, with lysine 247 being absolutely essential. Mutation of either lysine 247 or 195 to cysteine, and treatment of the mutant enzyme with 2-bromethylamine, resulted in the recovery of substantial enzyme activity. The effects of the site-directed alkylating inhibitor, 5-chlorolaevulinic acid, and 4,7-dioxosebacic acid, a putative intermediate analogue, were investigated by X-ray crystallography. These inhibitors reacted with both active-site lysine residues. The role of these two lysine residues in the enzyme mechanism is discussed
The x-ray structure of yeast 5-aminolaevulinic acid dehydratase complexed with substrate and three inhibitors
No full textThe structures of 5-aminolaevulinic acid dehydratase (ALAD) complexed with substrate (5-aminolaevulinic acid) and three inhibitors: laevulinic acid, succinylacetone and 4-keto-5-aminolaevulinic acid, have been solved at high resolution. The ligands all bind by forming a covalent link with Lys263 at the active site. The structures define the interactions made byone of the two substrate moieties that bind to the enzyme during catalysis. All of the inhibitors induce a significant ordering of the flap covering the active site. Succinylacetone appears to be unique by inducing a numberof conformational changes in loops covering the active site, which may be important for understanding the co-operative properties of ALAD enzymes. Succinylacetone is produced in large amounts by patients suffering from the hereditary disease type I tyrosinaemia and its potent inhibition of ALAD also has implications for the pathology of this disease. The most intriguing result is that obtained with 4-keto-5-aminohexanoic acid, which seems to form a stable carbinolamine intermediate with Lys263. It appears that we have defined the structure of an intermediateof Schiff base formation that the substrate forms upon binding to the P-site of the enzyme
Breastfeeding attitudes and knowledge among sixth year medical students in Jordan
No full textBackground: Previous reports have demonstrated that counseling about breastfeeding can improve the rate and initiation duration of breastfeeding. However, those medical students are ill-prepared for this role. It is unclear whether medical students would provide the knowledge and skills necessary for effective breastfeeding promotion or not in Jordan. The aim of this study was to identify breastfeeding attitudes and knowledge among 6th year medical students in their final year at The Jordan University of Science and Technology (JUST).Methods: A 28-item self-administered questionnaire; containing three sections: knowledge (13 items) attitude (7 items) and demographic (3 items), were distributed randomly to medical students. The random sample consisted of 234 medical students who were in their final year. The questionnaire assessed both breastfeeding attitudes and knowledge.Results: The results were explained taking into consideration gender and being a parent. Mean attitude's score for participants without children was 46.7 as compared to 44.0 for those with children. The results showed similar negative attitude toward breastfeeding among both male and female participants regardless of having children or not (p=0.35). This means that there were no significant difference in attitudes toward breastfeeding among male and female students whether they are having children or not. On the other hand, the mean knowledge score was 22.9 for male participants while it was 21.55 for female participants, indicating some degree of breastfeeding knowledge among participants (p=0.035). However, having personal experience with breastfeeding (self or partner) did not increased breastfeeding attitudes and knowledge (p=0.35 vs. p=0.93, respectively).Conclusions: Medical students have significant educational needs in the area of breastfeeding management and breastfeeding education. Further targeted training is needed to improve both breastfeeding attitudes and knowledge
[Correspondence Between M. P. Parr and Barbara Jordan - October 14-18, 1974]
No full textTelegram from a constituent in Houston asking Barbara Jordan to vote to override the President's veto on the Railroad Retirement Act with a reply from Jordan saying that she did and that the Act became law
5-Aminolevulinic acid synthase: mechanism, mutations and medicine
No full text5-Aminolevulinic acid synthase (ALAS), the first enzyme of the heme biosynthesis pathway, catalyses the pyridoxal 5'-phosphate-dependent condensation between glycine and succinyl-CoA to yield 5-aminolevulinic acid (5-amino-4-oxopentanoate). A three-dimensional structural model of Rhodobacter spheroides ALAS has been constructed and used to identify amino acid residues at the active site that are likely to be important for the recognition of glycine, the only amino acid substrate. Several residues have been investigated by site-directed mutagenesis and enzyme variants have been generated that are able to use alanine, serine or threonine. A three-dimensional structure model of 5-aminolevulinic acid synthase from human erythrocytes (ALAS 2) has also been constructed and used to map a range of naturally occurring human mutants that give rise to X-linked sideroblastic anemia. A number of these anemias respond favourably to vitamin B(6) (pyridoxine) therapy, whereas others are either partially responsive or completely refractory. Detailed investigations with selected human mutants have highlighted the importance of arginine-517 that is implicated in glycine carboxyl group binding
Advancing nursing? Master's level nurses in Jordan
No full textThe aim of the study was to examine the extent to which advanced nursing practice was evident in Jordan, with a particular focus on the contribution of Master’s level nurses to advancing practice. It also aimed at understanding the drivers for developing its roles and the factors which might facilitate or hinder their implementation.
The study used an ethnographic design in which qualitative and quantitative methods of data collection were used. The study comprised two stages. The first stage involved interviewing key stakeholders and surveying M-level nurses. Stage two involved interviewing and observing M-level nurses working in clinical practice in five Jordanian hospitals and interviewing the main stakeholders with whom those nurses had contact.
Three themes emerged from the data: understanding advanced nursing practice, becoming am M-level nurse, and being an M-level nurse. The analysis showed that there was no clear notion of advanced nursing practice in Jordan, although participants did describe a number of different elements of advanced practice. The analysis also revealed that nurses undertake Master’s degrees for professional and self-development reasons. The most frequently cited benefits from M-level education that reflected on practice were the enhancement of cognitive abilities, including critical thinking, problem solving and the questioning of practice, the use of research skills and in-service training. The area with least change was that of the development of new practical skills. The data also suggested that a change of job title or job description, after gaining a Master’s degree, reflects the movement of M-level nurses away from direct patient care to non-direct patient care.
Several factors were identified as facilitating or hindering the development of the role of M-level nurses in practice. These were organisational factors, professional factors, and personal attributes. The most significant factors were lack of recognition of the M-level nurse, and the subservient role of the nurse in Jordanian society
Political participation in Jordan: the impact of party and tribal loyalties since 1989
No full textIn the light of the internal and regional crises in the 1980s, Jordan found itself under pressure, and various ideological and political factors pushed the country towards political reform. As a result, Jordan has undergone several transformations, and a certain degree of political liberalization has made political participation the main objective of the Jordanian political system and its various institutions. This development in turn has required participation of all segments of the society, including political parties, minorities, and women. This participation demonstrates how far the political system has been liberalized. Therefore, nobody can argue that there is no political participation in Jordan. However, important questions remain. What is the form of this participation? What is its scale? What factors influence political participation, and what are its main objectives? Therefore, the purpose of this study was to explore the issue of political participation in Jordan. In particular, it investigated the impact of party and tribal loyalties on political participation in Jordan since 1989. This is undertaken through examining the basic forms of political participation, particularly participation in parliamentary elections. Accordingly, this study is divided into two main parts. The first part aims to shed light on the historical development of Jordanian parliament, electoral laws and systems, and political parties' participation and in addition to examine these in context of the socio-economic, political, and cultural environment. The second part was carried out through a survey involving the distribution of 400 questionnaires to five groups of political elite in Jordan. It is concluded in this study that despite the fact that political parties in Jordan date back to the establishment of the state in 1921, the social relations of kinship and the tribe are still dominant and constitute the main motives for Jordanians to participate in parliamentary elections. Several factors explain this, but it is argued here that the most important is legislations, particularly the emergency laws which have heavily restricted political freedoms and activities
Narratives of ethnicity and nationalism : a case study of Circassians in Jordan
No full textThis research is an exploration of ethnic narratives of the Circassian
community in Jordan, in addition to the nationalist narratives promoted by the state
of Jordan, and their reconstruction by the research participants. This research aims to
understand how the research participants, as non-Arabs, understand and makes
sense of the Pan-Arab ethnonational narratives promoted by the state through the
‘Jordan First’ nationalist campaign and textbooks of national and civic education. It
also seeks to understand the ethnic narratives of the Circassian community. It
highlights the fact that ethnic narratives are often contextualised, and come to light
always in comparison to the other. It also shows how ethnic narratives are gendered,
can include or exclude women, and gender relations are ethnicised, or in other
words used as markers for group boundaries.
The main aim of this research is to unpack the research participants’
conceptualisations of Jordan and the Pan-Arabism, and to understand the strategies
they use to include themselves within these narratives. It intends to evaluate
whether research participants see themselves as integrated into the Jordanian society
or not. Whereas the community itself is often portrayed as integrated into the
society, because many of them are in high governmental positions, and the
ceremonial guards of the Royal Family are the Circassians, it is also important to
examine whether they believe that they are, and how. This thesis contributes to the
literature on ethnicity and nationalism based on a minority with unique profile, and
also contributes to the overall body of literature on state nationalism in the Middle
East. The research has been approached through the use of both qualitative and
quantitative data collection methods. It is based on the analysis of textbooks of
national and civic education, and the ‘Jordan First’ campaign, in addition to 13
interviews and 62 questionnaires
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