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M Parsons

Publications and source records attributed to M Parsons.

At least 91 records · Page 5Linked to original sources
PubMed1993

Characterization of a divergent glycosomal microbody phosphoglycerate kinase from Trypanosoma brucei.

There are 3 loci in the phosphoglycerate kinase (PGK) gene complex of Trypanosoma brucei. The PGK-A gene product, which we term 56PGK, is targeted to glycosomal microbodies and is highly homologous to the parasite's 2 known PGKs (one cytoplasmic and one glycosomal). However, 56PGK contains an 80 amino acid insertion as well as numerous substitutions compared to the other PGKs. The complementation and kinetic analyses described here demonstrate that 56PGK is an authentic phosphoglycerate kinase--the largest yet described. When expressed in Escherichia coli, 56PGK complements the pgk- phenotype. 56PGK was expressed as a fusion protein and purified to near homogeneity. The Michaelis constants are similar to those of other PGKs, being 0.12 and 2.4 mM for Mg-ATP and 3-phosphoglycerate, respectively. As with other T. brucei PGKs, ATP but not GTP or ITP can serve as a phosphate donor during catalysis. No evidence was obtained for phosphate transfer to atypical substrates. 56PGK shows sulfate inhibition at all concentrations tested, rather than the sulfate activation observed with yeast PGK.

Amino Acid Sequence↗
PubMed1993

Knowledge of AIDS and safer sex practices among college freshmen.

We assessed knowledge of the acquired immunodeficiency syndrome (AIDS) and of safer sex practices among college freshmen. A second purpose of the study was to assess this knowledge among black as well as white students. Students attending classes at three private colleges in a large southern city were asked to participate in the study. Respondents completed the modified AIDS information survey, the knowledge of safe sex practices questionnaire, and a demographic data sheet. A total of 689 questionnaires were received from single college freshmen. The results indicated that respondents were knowledgeable about the cause and transmission of AIDS but were less knowledgeable about medical aspects. Most knew that condoms are effective in preventing the spread of AIDS, but fewer could differentiate between the effectiveness of latex and nonlatex condoms. These findings are useful to health educators in improving AIDS education programs.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Preceptor workshops: a collaborative model.

Educational programs for nurses are becoming increasingly reliant on clinicians in hospitals and other health care agencies to act as preceptors for their students. Often there is no formal preparation for this role, nor are rewards provided by the educational institutions. This paper describes a collaborative effort between a university and a college program to prepare and reward nurses who work as preceptors with students in their settings.

Education, Nursing, Baccalaureate↗
PubMed1992

Cloning and expression of Trypanosoma cruzi ribosomal protein P0 and epitope analysis of anti-P0 autoantibodies in Chagas' disease patients.

Chagas' disease, caused by the intracellular protozoan parasite Trypanosoma cruzi, is a major cause of heart failure in endemic areas. Antigenic mimicry by T. cruzi antigens sharing epitopes with host macromolecules has been implicated in the pathogenesis which is thought to have a significant autoimmune component. We report herein on the cloning and characterization of a full-length cDNA from a T. cruzi expression library encoding a protein, TcP0, that is homologous to the human 38-kD ribosomal phosphoprotein HuP0. The T. cruzi P0 protein shows a clustering of residues that are evolutionarily conserved in higher eukaryotes. This includes an alanine- and glycine-rich region adjacent to a highly charged COOH terminus. This "hallmark" domain is the basis of the crossreactivity of the highly immunogenic eukaryotic P protein family. We found that T. cruzi-infected individuals have antibodies reacting with host (self) P proteins, as well as with recombinant TcP0. Deletion of the six carboxy-terminal amino acids abolished the reactivity of the T. cruzi infection sera with TcP0. This is similar to the specificity of anti-P autoantibodies described for a subset of patients with systemic lupus erythematosus (SLE) (Elkon, K., E. Bonfa, R. Llovet, W. Danho, H. Weissbach, and N. Brot. 1988. Proc. Natl. Acad. Sci. USA. 85:5186). These results suggest that T. cruzi P proteins may contribute to the development of autoreactive antibodies in Chagas' disease, and that the underlying mechanisms of anti-P autoantibody may be similar in Chagas' and SLE patients. This study represents the first definitive report of the cloning of a full-length T. cruzi antigen that mimics a characterized host homologue in structure, function, and shared antigenicity.

Amino Acid Sequence↗
PubMed1992

The refinding of theory in clinical practice.

The analyst's use of his preconscious is central to understanding how clinical practice in psychoanalysis is informed by theory. One view is that we have a definitive conception of our theory, from which we derive our clinical practice by largely preconscious deliberation. Another view sees psychoanalytic concepts as elastic, related to each other along dimensions of meaning in a finite but flexible theoretical space. We do not, on this view, determine once for all what our theory is, but continually have to discover it by exploring our preconscious as we watch ourselves at work. Some detailed clinical material shows how I observed the evolution of my use of theory in a particular case. I had to refind theory which I already knew; familiar concepts had to become surprising. This also allowed theoretical understanding to emerge which was new to me. This implies an act of personal engagement with our theoretical concepts, rather than the pseudo-objective application of what are taken for facts. A survey of various positions in the philosophy of science shows that this is entirely consistent with the nature of scientific activity.

Austria↗
PubMed1991

Distinct patterns of tyrosine phosphorylation during the life cycle of Trypanosoma brucei.

Regulation of tyrosine phosphorylation is a critical element in controlling growth and differentiation in higher eukaryotes. We have determined that the protozoan Trypanosoma brucei, which diverged early in the eukaryotic lineage, possesses multiple proteins which react with a specific anti-phosphotyrosine antiserum. Anti-phosphotyrosine immunoprecipitates of [32P]orthophosphate-labeled cells were shown to contain phosphotyrosine by two-dimensional electrophoresis. Western analysis of cells from different stages of the life cycle demonstrates the appearance of tyrosine-phosphorylated proteins at 40-42 kDa during the transition from slender to stumpy blood-forms. Growth of procyclic form cells in orthovanadate resulted in increased levels of specific tyrosine-phosphorylated proteins. The demonstration of phosphotyrosine-containing proteins in T. brucei and their differential regulation during the life cycle suggests that tyrosine kinases and phosphatases may play an important role in the biology of primitive protozoa.

Animals↗
PubMed1991

A phosphoglycerate kinase-like molecule localized to glycosomal microbodies: evidence that the topogenic signal is not at the C-terminus.

The phosphoglycerate kinase (PGK) gene complex of Trypanosoma brucei contains three tandemly linked related genes. One gene encodes a cytoplasmic PGK, while another encodes a PGK isozyme localized to glycosomal microbodies. In this communication, we report that the third gene in this complex encodes a 56-kDa molecule which is also localized to the glycosomal core. DNA sequence analysis indicates that this gene contains multiple substitutions and a large insertion in the amino domain, but that it is very similar to the other PGK isozymes in the carboxy domain. The C-terminal tripeptide is identical to that of the cytoplasmic isozyme, and only one conservative change occurs in the last 25 amino acids. The encoded protein, p56, thus contrasts with the many peroxisomal microbody proteins in which the C-terminal tripeptide contains sufficient information for targeting to peroxisomes. Multiple mechanisms may exist for targeting proteins to the protein cores of microbody organelles. Comparisons of the DNA sequences of several alleles suggest that homologous recombination plays a role in the generation of allelic diversity.

Alleles↗
PubMed1990

Microbody phosphoglycerate kinase of Trypanosoma brucei: expression and complementation in Escherichia coli.

In the primitive eukaryotic parasite, Trypanosoma brucei, most of the enzymes of glycolysis are located within microbody organelles called glycosomes. Proteins destined for the glycosome are synthesized on free ribosomes and post-translationally translocated into the organelle. The gene, gPGK, encoding the glycosomal isozyme of phosphoglycerate kinase (gPGK), was cloned adjacent to a T7 promoter and cotransformed with a plasmid encoding T7 RNA polymerase into Escherichia coli Pgk-cells. Functional complementation occurred, but only after the creation of a ribosome-binding site by mutagenesis. This represents the first example of complementation of an E. coli mutant with a gene encoding a microbody protein. Enzymatically active recombinant gPGK was purified to near homogeneity by ion exchange chromatography from highly expressing E. coli. The recombinant protein will aid in studies of glycosomal biogenesis.

Animals↗
PubMed1990

Trypanosoma brucei: two-dimensional gel analysis of the major glycosomal proteins during the life cycle.

Kinetoplastid organisms possess a unique organelle, the glycosome, which compartmentalizes the Embden-Meyerhof segment of glycolysis and several other metabolic pathways. In Trypanosoma brucei many of the enzyme activities localized to the glycosome are stage regulated. Two-dimensional gel analysis was used to examine the characteristics, expression, and biosynthesis of the major glycosomal proteins. Two-dimensional gel maps of glycosomes from slender bloodforms and late intermediate-stumpy bloodforms (the precursors of procyclic forms) were indistinguishable, while those of procyclic form glycosomes showed extensive differences. Glycosomal phosphoenolpyruvate carboxykinase and malate dehydrogenase were identified to have subunit molecular weights of 60 and 34 kDa, respectively. We detected two hitherto undescribed glycosomal proteins, one of which is found only in bloodforms. All of the major proteins, except glucose phosphate isomerase, were highly basic. Stage regulation of glycosomal enzyme activities correlated with stage regulation of specific protein biosynthesis.

Animals↗
PubMed1990

Leishmania gp63 molecule implicated in cellular adhesion lacks an Arg-Gly-Asp sequence.

The parasitic protozoa Leishmania are intracellular pathogens which enter host cells through largely undefined mechanisms. One molecule thought to play an important role in this process is gp63, the major glycoprotein on the surface of the infective promastigote form. We have cloned and analyzed the gp63 gene from Leishmania chagasi, an etiologic agent of acute visceral leishmaniasis. The predicted amino acid sequence is highly homologous to that reported for Leishmania major, with the exception of a 56-amino-acid region. This region in L. major was predicted to contain an arginine-glycine-aspartic acid (RGD) sequence that was subsequently hypothesized to be involved in binding to the host cell. The L. chagasi gene lacks this sequence or indeed any RGD sequence, and further studies failed to confirm the existence of an RGD sequence in the L. major gp63 gene. Binding to the host cell surface must therefore be mediated by other sequences in gp63 or by other components of the Leishmania promastigote.

Amino Acid Sequence↗
PubMed1990

Current concepts in stage-regulated gene expression in kinetoplastida.

The different physiological environments provided by the hosts probably generated a strong selective force for the evolution of differential expression of gene products in digenetic kinetoplastid parasites. Indeed, the sorts of molecules that would be predicted to be stage-regulated have been found to be differentially expressed. Examples include transport molecules, metabolic enzymes, molecules involved in cell adhesion and penetration, and molecules involved in evasion of host defence mechanisms. Within the life cycle, environmental cues provided by the host, such as temperature and nutrients, may also function as triggers for the differential expression of gene products.

Journal Article↗
PubMed1990

Some issues affecting termination. The treatment of a high-risk adolescent.

This paper addresses some of the difficulties of termination in the psychoanalytic psychotherapy of a deprived, high-risk adolescent girl, who had two previous treatments. Some commonly referred to issues are explored: termination and the developmental process of adolescence; the relationship between termination, mourning, and internalization; the need for the resolution of the transference and careful monitoring of the countertransference; the importance of the transference resolution of the oedipus complex and related issues concerning preoedipal development and identification; and the consolidation of ego strength.

Adolescent↗
PubMed1990

Characterization of an in vitro assay for import of 3-phosphoglycerate kinase into the glycosomes of Trypanosoma brucei.

Glycosomes are microbody organelles found in kinetoplastida, where they serve to compartmentalize the enzymes of the glycolytic pathway. In order to identify the mechanism by which these enzymes are targeted to the glycosome, we have modified the in vitro import assay developed by Dovey et al. (Proc. Natl. Acad. Sci. USA 85:2598-2602, 1988). This assay measures the uptake of in vitro-translated Trypanosoma brucei glycosomal 3-phosphoglycerate kinase (gPGK) by purified glycosomes. Up to 50% of the total 35S-gPGK in the glycosomal fraction was resistant to extraction by 3 M urea or treatment with proteinase K (500 micrograms/ml). The glycosome-associated 35S-gPGK could be chemically cross-linked to the endogenous glycosomal proteins to form a sodium dodecyl sulfate-resistant complex, suggesting that it is close to the intraglycosomal protein matrix. Deoxycholate solubilized the glycosome and thereby rendered the glycosome-associated 35S-gPGK fully susceptible to proteinase K. However, the glycosome-associated 35S-gPGK was not digested by proteinase K in the presence of Triton X-100, which cannot dissolve the glycosomal protein core. The 35S-gPGK synthesized in vitro was able to bind directly to protein cores, where it became resistant to urea extraction and proteinase K digestion. However, the 35S-gPGK-protein core complex exhibited a much higher density than the 35S-gPGK-glycosome complex and was readily separable in sucrose gradients. Thus, in our in vitro import assay, the 35S-gPGK appeared to associate with intact glycosomes, possibly reflecting import of protein into the organelle. Complete denaturation of the 35S-gPGK in 8 M urea prior to the assay enhanced the efficiency of its association with glycosomes. Native gPGK did not compete with the association of in vitro-translated gPGK unless it was denatured. The assay exhibited time and temperature dependence, but it did not require externally added ATP and was not inhibited by the nonhydrolyzable analogs adenosine-5'-(beta,gamma-imido)-triphosphate and gamma-S-ATP. However, the presence of 20 to 30 microM ATP inside the glycosome may fulfill the requirement for protein import.

Animals↗
PubMed1989

Elevated phosphoglycerate kinase mRNA but not protein in monomorphic Trypanosoma brucei: implications for stage-regulation and post-transcriptional control.

Phosphoglycerate kinase (PGK) is present in high levels in the glycosomes of bloodstream stage Trypanosoma brucei, but is virtually absent in procyclic stage glycosomes. Glycosomes isolated from slender and stumpy stage bloodforms show similar levels of PGK, although levels are slightly lower in stumpy forms. Lower levels of glycosomal PGK transcripts are observed in stumpy form RNA, paralleling the decrease in glycosomal PGK activity. Monomorphic strains and pleiomorphic strains show similar glycosomal PGK activity, but monomorphic strains have much higher levels of the glycosomal PGK transcript. In three separate cases, predominantly monomorphic strains derived from highly pleiomorphic strains showed increased levels of glycosomal PGK (gPGK) mRNA. gPGK synthesis rates in monomorphic and pleiomorphic strains were similar, and no significant differences in turnover were observed. These data suggest the possibility of translational control of gPGK protein levels in trypanosome bloodforms. The data also indicate that the metabolism of gPGK mRNA in highly passaged laboratory strains is altered, and counsel caution when attributing differences in transcript levels to stage-specific regulation.

Animals↗