Search PubMed⌕ Search

Biomedical subjects

A Boyd

Publications and source records attributed to A Boyd.

At least 55 records · Page 3Linked to original sources
PubMed1995

Localization of a protein A-tagged Kex2 protein to the vacuole of Saccharomyces cerevisiae allows rapid purification of vacuolar membranes.

We have previously reported an immunoisolation procedure which allows purification of Kex2p-containing Golgi membranes from lysed yeast cells. In order to evaluate the use of tagging procedures in organelle isolation we set out to isolate the same Golgi membrane fraction using a version of the Kex2 protease that had been affinity-tagged at its C-terminus. This protein is found to be localized in the vacuole, providing the basis of a method for the affinity-purification of vacuolar membranes.

Base Sequence↗
PubMed1995

Pseudomonas aeruginosa biofilms: role of the alginate exopolysaccharide.

Pseudomonas aeruginosa synthesizes an exopolysaccharide called alginate in response to environmental conditions. Alginate serves to protect the bacteria from adversity in its surroundings and also enhances adhesion to solid surfaces. Transcription of the alginate biosynthetic genes is induced upon attachment to the substratum and this leads to increased alginate production. As a result, biofilms develop which are advantageous to the survival and growth of the bacteria. In certain circumstances, P. aeruginosa produces an alginate lyase enzyme which cleaves the polymer into short oligosaccharides. This negates the anchoring properties of the alginate and results in increased detachment of the bacteria away from the surface, allowing them to spread and colonize new sites. Thus, both alginate biosynthetic and degradative enzymes are important for the development, maintenance and spread of P. aeruginosa biofilms.

Alginates↗
PubMed1995

Bromocriptine and psychosis: a literature review.

Bromocriptine is an ergot-derived dopamine agonist. Its current uses include the treatment of Parkinson's disease, postpartum ablaction, prolactinomas, acromegaly, and amenorrhea and galactorrhea secondary to neuroleptic use. It is often reported to produce psychiatric side effects such as confusion, hallucinations, and delusions. The literature is reviewed and supports a strong anecdotal relationship between bromocriptine use and psychosis.

Amenorrhea↗
PubMed1995

High sun protection factor sunscreens in the suppression of actinic neoplasia.

BACKGROUND AND DESIGN: A controlled trial was undertaken from December 1987 to December 1990 to test the hypothesis that a strong sunscreen can reduce the number of cancerous and precancerous skin lesions. Candidates were selected from a high-risk population attending either a university- or Veterans Affairs-based dermatology practice in Lubbock, Tex, for a prospective, double-blind, controlled trial of daily application of sunscreen vs placebo over a 2-year period. Participants were asked to volunteer if they had demonstrated premalignant changes (actinic keratoses) or nonmelanoma skin cancer (basal cell carcinoma or squamous cell carcinoma), had continuing sun exposure, and were not using sunscreen on a regular basis. Fifty-three volunteers were initially enrolled in the study, and 37 came for the final 24-month visit. RESULTS: The rate of appearance of new precancerous skin lesions was less for the treatment group than for control subjects. People with darker skin had fewer actinic keratoses, women had fewer lesions than men, and people with fewer lesions at enrollment had fewer lesions during the study. The numbers of new nonmelanoma skin cancers appearing during the study period were too small for statistical analysis. CONCLUSIONS: The regular use of sunscreens can significantly reduce cutaneous neoplasia, as indicated by its suppression of precancerous lesions. A longer and/or larger study would be necessary to demonstrate an effect on malignant lesions.

Adult↗
PubMed1994

Identification of amino acid residues involved in the activity of phosphomannose isomerase-guanosine 5'-diphospho-D-mannose pyrophosphorylase. A bifunctional enzyme in the alginate biosynthetic pathway of Pseudomonas aeruginosa.

Phosphomannose isomerase-guanosine 5'-diphospho-D-mannose pyrophosphorylase (PMI-GMP), which is encoded by the algA gene, catalyzes two noncontiguous steps in the alginate biosynthetic pathway of Pseudomonas aeruginosa; the isomerization of D-fructose 6-phosphate to D-mannose 6-phosphate and the synthesis of GDP-D-mannose and PPi from GTP and D-mannose 1-phosphate. Amino acids that are required for the GMP enzyme activity were identified through site-directed mutagenesis of the algA gene. Mutation of Lys-175 to arginine, glutamine, or glutamate produced an enzyme whose Km for D-mannose 1-phosphate was 470-3,200-fold greater than that measured for the wild type enzyme. In addition, these mutant enzymes had a lower Vmax for the GMP activity as compared with the wild type PMI-GMP. These results indicate that Lys-175 is primarily involved in the binding of the substrate D-mannose 1-phosphate, although it is likely that other residues are required for the specificity of binding. Mutation of Arg-19 to glutamine, histidine, or leucine resulted in a 2-fold lower Vmax for the GMP enzyme activity and a 4-7-fold increase in the Km for GTP as compared with the wild type enzyme. Thus, it appears that Arg-19 functions in the binding of GTP. In addition, chymotryptic digestion of PMI-GMP showed that the carboxyl terminus is critical for PMI activity but not for GMP activity. Taken together, these results support the hypothesis that the bifunctional PMI-GMP protein is composed of two independent enzymatic domains.

Alginates↗
PubMed1994

Role of alginate lyase in cell detachment of Pseudomonas aeruginosa.

The exopolysaccharide alginate of Pseudomonas aeruginosa was shown to be important in determining the degree of cell detachment from an agar surface. Nonmucoid strain 8822 gave rise to 50-fold more sloughed cells than mucoid strains 8821 and 8830. Alginate anchors the bacteria to the agar surface, thereby influencing the extent of detachment. The role of the P. aeruginosa alginate lyase in the process of cell sloughing was investigated. Increased expression of the alginate lyase in mucoid strain 8830 led to alginate degradation and increased cell detachment. Similar effects were seen both when the alginate lyase was induced at the initial stage of cell inoculation and when it was induced at a later stage of growth. It appears that high-molecular-weight alginate polymers are required to efficiently retain the bacteria within the growth film. When expressed from a regulated promoter, the alginate lyase can induce enhanced sloughing of cells because of degradation of the alginate. This suggests a possible role for the lyase in the development of bacterial growth films.

Agar↗
PubMed1994

Venous embolization after deflation of lower extremity tourniquets.

Massive pulmonary embolism has been reported to occur with the use of lower extremity tourniquets. We used transesophageal echocardiography to determine the incidence of venous embolism during lower extremity orthopedic surgery performed with a pneumatic tourniquet. The hemodynamic and respiratory consequences of all embolic events were assessed. Venous emboli were detected after tourniquet deflation in 8 of 30 procedures. The incidence of embolism was unrelated to the type of surgical procedure performed or the duration of tourniquet inflation. There were no significant differences in preoperative characteristics or postdeflation hemodynamic and respiratory responses between patients with and without emboli. Venous embolization is a relatively common event after tourniquet deflation. The clinical significance of these events remains to be determined.

Adult↗
PubMed1993

Sequence of the algL gene of Pseudomonas aeruginosa and purification of its alginate lyase product.

The alginate lyase-encoding gene (algL) of Pseudomonas aeruginosa was localized to a 1.7-kb EcoRI-XbaI fragment within the alginate biosynthetic gene cluster at 34 minutes on the chromosome. The nucleotide sequence of this DNA fragment revealed an ORF encoding a protein of M(r) 40,885 which is transcribed in the same orientation as the other alg genes within the biosynthetic gene cluster. The predicted protein has a potential N-terminal signal peptide which is consistent with its proposed periplasmic location. The AlgL protein was overproduced in Escherichia coli and purified. The purified protein was shown to have alginate lyase activity. In addition, an algL insertion mutant of the mucoid P. aeruginosa 8830 was constructed. This mutant (alm1) had a nonmucoid phenotype due to a polar effect on the transcription of an essential alg gene, algA. Thus, the algL gene is located within a region of the alginate biosynthetic gene cluster that appears to be non-essential for alginate production.

Alginates↗
PubMed1993

Molecular characterization of the SEC1 gene of Saccharomyces cerevisiae: subcellular distribution of a protein required for yeast protein secretion.

Strains of Saccharomyces cerevisiae harbouring temperature-sensitive mutations in the SEC1 and SEC5 genes exhibit an accumulation of post-Golgi secretory vesicles at 37 degrees C. We have cloned a fragment of yeast DNA which carries two distinct genes, one of which complements a sec1 mutation, and the other a sec5 mutation. Genetic test confirm that the sec1-complementing gene is indeed SEC1, and is essential for cell growth. Nucleotide sequence analysis reveals that the cloned SEC1 gene is the same as a previously sequenced sec1-complementing gene. The SEC1 sequence encodes a protein of 724 amino acids with a predicted molecular mass of 83 kDa. Antibodies purified from a polyclonal antiserum raised against the protein product of the cloned gene recognize a yeast protein of apparent molecular mass 78 kDa which is found in a detergent-resistant association with a rapidly sedimenting yeast subcellular fraction, behaviour which is suggestive of an interaction with a component of the yeast cytoskeleton.

Cloning, Molecular↗
PubMed1993

Surface antigens of human thymocyte populations defined by CD3, CD4 and CD8 expression: CD1a is expressed by mature thymocytes but not peripheral T cells.

Three colour flow cytometric analysis has been used to analyze the expression of a series of surface antigens on human thymic and peripheral T-cell populations. CD4, CD8 and CD3 were used to divide the populations into the conventional major categories, and the distribution of CD1a, CD2, CD7, CD34, CD44, class I MHC and class II MHC was then determined. Some characteristics of 'single positive' (CD4+8- and CD4-8+) T-lineage cells were unexpected. Amongst thymocytes, some 'immature single positives' were delineated as larger sized cells lacking cell surface CD3 and expressing low levels of class I MHC; however, in contrast with murine thymocytes, these were all CD4+8-, rather than being predominantly CD4-8+. Amongst peripheral T cells, a small proportion of CD7- cells were detected, within both the CD4+8-3+ and the CD4-8+3+ categories. Finally, in contrast to previous conclusions, CD1a was expressed at high levels on mature (CD4+8-3+ and CD4-8+3+) human thymocytes, although in agreement with previous reports it was absent from peripheral T cells. CD1a is therefore a useful marker of post-selection, post-thymic T-cell maturation.

Adolescent↗
PubMed1993

Effects of long-term food restriction on energy expenditure and thermoregulation in broiler-breeder fowls (Gallus domesticus).

1. From 2 to 21 weeks of age, 150 female broiler-breeder chicks received one of three dietary treatments. Fifty received an ad libitum supply of food (treatment AL). The remaining 100 were given weighed (restricted) rations once a day, 50 receiving the amount per bird recommended in the Ross 1 Parent Stock Management Manual (treatment R) and the other 50 receiving twice this recommended amount (treatment 2R). Water was provided ad libitum for all treatment groups. 2. The daily allowance for R birds increased from 26 g per bird at 2 weeks of age to 94 g at 21 weeks. The intake of AL birds meanwhile increased from 65 g at 2 weeks to 240 g at 19 weeks, before decreasing to about 200 g at 21 weeks. 3. Median heat productions (H) per bird in the R and 2R treatment groups were, respectively, 65 and 40% lower than in the AL when adjustment was made for the reduced food intake of AL birds in the calorimeter chambers. The effects of dietary treatment on fasting H were proportionally similar. 4. Because the increasing divergence in body weights would have made a large contribution to differences in H per bird, the results were adjusted to the median weight of 2.03 kg and to unit weight (1.00 kg). Adjusted fasting heat production was 18 and 11% less in 2R and R birds than in those fed ad libitum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1993

Nucleotide sequence and expression of the Pseudomonas aeruginosa algF gene controlling acetylation of alginate.

Colonization of the cystic fibrosis lung by Pseudomonas aeruginosa is greatly facilitated by the production of an exopolysaccharide called alginate. In this study we determined the nucleotide sequence of an alginate modification gene, algF, which controls the addition of acetyl groups to alginate. Expression of algF using a T7 promoter-expression system showed that algF codes for a 24.5 kDa polypeptide (predicted size 22,832 Da) that is processed to 19.5 kDa. The N-terminus of the processed polypeptide matched the predicted amino acid sequence of AlgF starting at Asp-29. An algF mutant failed to produce alginate owing to a polar effect on the downstream algA gene. Although the algA gene, provided in trans, restored synthesis of alginate, the alginate was non-acetylated. We show that a plasmid containing both the algF and algA gene complements the alginate acetylation defect of the algF mutant strain.

Acetylation↗
PubMed1993

Immunoisolation of Kex2p-containing organelles from yeast demonstrates colocalisation of three processing proteinases to a single Golgi compartment.

One of the Golgi compartments of Saccharomyces cerevisiae is defined by the presence of a specific endoproteinase, Kex2p, which cleaves precursor polypeptides at pairs of basic residues. We have used antibodies directed against the cytoplasmically disposed C-terminal domain of Kex2p to develop an immuno-affinity procedure for the isolation of Kex2p-containing organelles. The method gives a high yield of sealed organelles that are essentially free of contamination from other secretory pathway organelles while being significantly enriched for two other late Golgi enzymes, dipeptidylaminopeptidase A and the Kex1 carboxypeptidase. Our findings provide clear evidence for a single yeast Golgi compartment containing all three late-processing enzymes, which is likely to be the functional equivalent in yeast of the mammalian trans-Golgi network.

Carboxypeptidases↗
PubMed1992

Evidence for the indirect utilization of glucose for the synthesis of hepatic glycogen in man.

1. This study was designed to test the hypothesis that three-carbon intermediates can be used in the 'indirect' pathway of glycogen synthesis in human liver (i.e. a route additional to the use of glucose by the 'direct' pathway). 2. After an overnight fast, 13 patients were given an infusion of 20% (w/v) glucose before elective abdominal operation. All received a 2.5 g bolus of 2220 kBq of selectively 3H- and 14C-labelled glucose before removal of a 1 g biopsy of liver. 3H and 14C were determined in purified glycogen as well as in glucose and lactate from samples of peripheral blood. 3. The ratio and specific activities of 3H and 14C in glycogen were found to be significantly lower than those in administered glucose. By calculation, 7-74% of glycogen repletion occurred by indirect pathways and not all of this was from the glucose supplied. 4. This study suggests that the operation of a direct pathway in man is not exclusive and that significant repletion of hepatic glycogen occurs by an indirect route.

Adult↗