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Biomedical subjects

T Page

Publications and source records attributed to T Page.

At least 37 records · Page 2Linked to original sources
PubMed1997

FCA, a gene controlling flowering time in Arabidopsis, encodes a protein containing RNA-binding domains.

A strong promoter of the transition to flowering in Arabidopsis is encoded by FCA. FCA has been cloned and shown to encode a protein containing two RNA-binding domains and a WW protein interaction domain. This suggests that FCA functions in the posttranscriptional regulation of transcripts involved in the flowering process. The FCA transcript is alternatively spliced with only one form encoding the entire FCA protein. Plants carrying the FCA gene fused to the strong constitutive 35S promoter flowered earlier, and the ratio and abundance of the different FCA transcripts were altered. Thus, FCA appears to be a component of a posttranscriptional cascade involved in the control of flowering time.

Amino Acid Sequence↗
PubMed1997

Glucose-lowering effect of BTS 67 582.

1. The hypoglycaemic effect of BTS 67 582 (1,1-dimethyl-2(2-morpholinophenyl) guanidine fumarate) was studied in normal rats. 2. BTS 67 582 (100 mg kg(-1), p.o.) acutely lowered basal plasma glucose concentrations: onset within 1 h, maximum decrease of >40% at 2-3 h, and partial return to euglycaemia by 5 h. Plasma insulin concentrations were increased: onset within 30 min, maximum increase 3 fold at 1-2 h; returning to normal by 5 h. 3. BTS 67 582 (100 mg kg(-1)) increased (by 56%) the rate of disappearance of plasma glucose during an intravenous glucose tolerance test, accompanied by a 51% increase in insulin concentrations. 4. During hyperglycaemic clamp studies BTS 67 582 (100 mg kg(-1)) increased glucose utilization 3 fold. This was associated with a 3 fold increase in insulin concentrations, even in the presence of adrenaline at a dosage which inhibits glucose-induced insulin release. 5. When the insulin-releasing effect of BTS 67 582 (100 mg kg(-1)) was inhibited by infusion of somatostatin, there was no effect on glycaemia. 6. Insulin-dependent diabetic BB/S rats, which do not produce endogenous insulin, showed no effect of BTS 67 582 (100 mg kg(-1)) on plasma glucose concentrations in the presence or absence of exogenous insulin. 7. The results demonstrate an acute hypoglycaemic effect of BTS 67 582 which appears to result mainly from its potent insulin-releasing action.

Animals↗
PubMed1997

Microplate assay of ascorbic acid in aqueous humor with bicinchoninic acid.

An inexpensive microplate assay method was developed to determine ascorbic acid in human aqueous humor samples. The method is based on the selective oxidation of ascorbic acid at alkaline pH and determination of ascorbic acid and other reducing substances in samples with bicinchoninic acid/CuSO4 before and after the alkaline treatment. The two-point measurement eliminates the effect of interfering substances, such as glucose, uric acid and glutathione, which are stable at alkaline pH. The advantages of the method are that it requires small sample volumes and allows handling of a large number of samples simultaneously.

Aqueous Humor↗
PubMed1997

Increased Ac excision (iae): Arabidopsis thaliana mutations affecting Ac transposition.

The maize transposable element Ac is highly active in the heterologous hosts tobacco and tomato, but shows very much reduced levels of activity in Arabidopsis. A mutagenesis experiment was undertaken with the aim of identifying Arabidopsis host factors responsible for the observed low levels of Ac activity. Seed from a line carrying a single copy of the Ac element inserted into the streptomycin phosphotransferase (SPT) reporter fusion, and which displayed typically low levels of Ac activity, were mutagenized using gamma rays. Nineteen mutants displaying high levels of somatic Ac activity, as judged by their highly variegated phenotypes, were isolated after screening the M2 generation on streptomycin-containing medium. The mutations fall into two complementation groups, iae1 and iae2, are unlinked to the SPT::Ac locus and segregate in a Mendelian fashion. The iae1 mutation is recessive and the iae2 mutation is semi-dominant. The iae1 and iae2 mutants show 550- and 70-fold increases, respectively, in the average number of Ac excision sectors per cotyledon. The IAE1 locus maps to chromosome 2, whereas the SPT::Ac reporter maps to chromosome 3. A molecular study of Ac activity in the iae1 mutant confirmed the very high levels of Ac excision predicted using the phenotypic assay, but revealed only low levels of Ac re-insertion. Analyses of germinal transposition in the iae1 mutant demonstrated an average germinal excision frequency of 3% and a frequency of independent Ac re-insertions following germinal excision of 22%. The iae mutants represents a possible means of improving the efficiency of Ac/Ds transposon tagging systems in Arabidopsis, and will enable the dissection of host involvement in Ac transposition and the mechanisms employed for controlling transposable element activity.

Arabidopsis↗
PubMed1996

Simple reversed-phase high-performance liquid chromatography quantitation of ganciclovir in human serum and urine.

A fast, simple, and cost-effective HPLC method for the quantitation of the antiviral drug ganciclovir is described. The serum samples are extracted with perchloric acid and neutralized with potassium phosphate buffer, and urine samples are diluted with distilled water. A reversed-phase column with isocratic elution by 15 mM potassium phosphate buffer (pH 2.5) containing 0.25% acetonitrile is used to separate ganciclovir; quantitation is by UV absorbance at 254 nm. Total turnaround time is 22 min; more than 3000 samples can be run on a single column without loss of peak quality. The limit of quantitation is 0.05 micrograms/ml. Recoveries varied from 91 to 107% with coefficients of variation ranging from 0.387 to 7.95%.

Antiviral Agents↗
PubMed1996

Use of Ac as an insertional mutagen in Arabidopsis.

A pilot-scale transposon mutagenesis experiment using a modified autonomous Activator (Ac) element, Ac delta Nael, was carried out in Arabidopsis thaliana. Four different transformants carrying Ac elements in different and defined genomic locations were used to generate 1000 plants carrying approximately 500 independent germinal transposition events. These plants were then selfed and the 1000 families screened in tissue culture and soil for phenotypic mutants. Fifty different families segregated mutations in their progeny. Preliminary Southern blot analysis of 29 families which segregated mutant progeny, showed that 28 had a transposed Ac. Six of the families were further tested for linkage between the transposed Ac and the mutant phenotype, and instability of the putatively tagged locus. Two of the mutants were shown to be tagged as they were tightly linked to a transposed Ac, and somatic and germinal reversion was associated with loss of Ac. One other mutant locus was shown to be closely linked to a transposed Ac, and therefore was likely to be tagged. The remaining three mutations were not tagged as they were not linked to a transposed Ac. In two of the tagged mutants Ac had transposed to closely linked sites, while in a third mutant the co-segregating Ac had transposed to a site which was not tightly linked to the donor T-DNA. Multiple insertions into the DIF1 locus were found, due to the preferential transposition of Ac to a linked site.

Arabidopsis↗
PubMed1996

Purification and characterization of human lymphoblast N-acetylglucosamine-1-phosphodiester alpha-N-acetylglucosaminidase.

The enzyme N-acetylglucosamine-1-phosphodiester alpha-N-acetylglucosaminidase (EC 3.1.4.45; uncovering enzyme) catalyzed the removal of N-acetylglucosamine from the N-acetylglucosamine-alpha-phospho-mannose portion of selected lysosomal enzyme oligosaccharide chains, thereby forming the mannose 6-phosphate signal which is responsible for the targeting of these lysosomal enzymes for transport into lysosomes. The uncovering enzyme has been purified approximately 7000-fold to electrophoretic homogeneity from Epstein-Barr virus-transformed human lymphoblast cells. The purification sequence involves solubilizing this membrane-bound enzyme with Tergitol NP-10, affinity chromatography on Lentil lectin-Sepharose 4B, ion-exchange chromatography on DEAE-Sephacel, chromatography on zinc(II)-IDA-Sepharose 6B, and preparative SDS-PAGE electrophoresis. The purified enzyme migrated as a single band of 114 kDa which was coincident with enzyme activity on analytical SDS-PAGE electrophoresis. Characterization studies of the purified enzyme demonstrated that catalytic activity was maximal at pH 6.95 and that the enzyme retained full activity following incubation for 10 min at 60 degrees C. No requirement was found for a divalent cation, but Zn2+, Hg2+, and Cu2+ were found to reduce the enzyme's activity by 30-40%. The highest catalytic efficiency was observed with N-acetylglucosamine-phospho-methylmannoside as a substrate while uridine diphosphate-N-acetylglucosamine, N-acetylglucosamine-phosphomannose-uteroferrin, and N-acetylglucosamine-phosphate were also cleaved by the enzyme with decreasing efficiency. Acetamino-deoxycastanospermine was a potent inhibitor of the human enzyme with a Ki of 0.35 microM, while N-acetylglucosamine phosphate (Ki 1.58 mM) and N-acetylglucosamine (Ki 5.1 mM) inhibited the enzyme to a lesser degree.

Chromatography, Affinity↗
PubMed1995

Ocular health status of chemical industrial workers.

BACKGROUND: Approximately 1.2 million workers are employed within chemical industries throughout South Africa. Very little basic data exists regarding the ocular health status and prevalence of occupationally related eye disorders of these workers. METHOD: A questionnaire was administered and an ocular health examination was carried out on 78 workers in a chemical factory. Workers and the ocular disorders found were then classified according to those exposed and those not exposed to chemicals. RESULTS: Ocular disorders were more prevalent in exposed workers (73.1%) than in nonexposed workers (43.6%). Statistically significant differences between exposed and nonexposed workers were found with respect to the prevalence of certain anterior segment disorders, viz., tear disorders, dry eye conditions, allergic conjunctivitis, and conjunctival melanosis. In respect to the prevalence of ocular disorders found, 40.8% were attributed to occupational exposure to chemicals. CONCLUSION: This pilot study shows that further research is required to explore the cause-effect relation between chemical exposure and development of certain anterior segment disorders. Occupational exposure to chemicals should be reduced and exposure protocols at work need to be revised in order to reduce the prevalence of occupationally related eye disorders.

Adult↗
PubMed1994

Importance of the intestine as a site of metformin-stimulated glucose utilization.

1. The intestine has been implicated as a site of increased glucose utilization by the antihyperglycaemic drug, metformin. This study makes a quantitative assessment of this effect. 2. Glucose utilization by the intestine and hind limb region was determined by arterial-venous glucose difference adjusted for blood flow rate in fasted rats receiving a hyperglycaemic hyperinsulinaemic infusion. 3. Intrajejunal administration of metformin, 250 mg kg-1, increased glucose disposal during the infusion procedure, associated with increased glucose utilization in the intestine by 69% and in the hind limb region by 40%. 4. Metformin, 250 mg kg-1, increased glucose disappearance during an intravenous glucose tolerance test. This was accompanied by increased uptake of tritiated 2-deoxy-D-glucose into the intestinal mucosa to a greater extent than into skeletal muscles (per unit wet weight of tissue). 5. The results demonstrate that the intestinal mucosa is a quantitatively important site of increased glucose utilization during the blood glucose-lowering effect of metformin.

Animals↗
PubMed1993

Identification of a mobile endogenous transposon in Arabidopsis thaliana.

A mobile endogenous transposable element, Tag1, has been identified in the plant Arabidopsis thaliana. Tag1 was found in the nitrate transporter gene, CHL1, of a chlorate-resistant mutant present in a population of plants containing an active maize Ac transposon. Tag1 excises from the chl1 gene producing chlorate-sensitive revertants with Tag1 or Tag1-related elements at different loci. Tag1 and related elements are present in the Landsberg but not Columbia or Wassilewskija ecotypes of Arabidopsis. Thus, Tag1 provides a tool for the insertional mutagenesis of plant genes essential for biological processes of agronomic importance.

Arabidopsis↗
PubMed1993

Antilipid a monoclonal antibody HA-1A: immune complex clearance of endotoxin reduces TNF-alpha, IL-1 beta and IL-6 production.

HA-1A is a human monoclonal IgM antibody which recognizes the lipid A component of lipopolysaccharide (LPS). This antibody has reduced mortality in the septic shock syndrome resulting from Gram negative bacteria, in which many of the manifestations are considered to be due to cellular activation and secretion of cytokines, most notably TNF-alpha. However HA-1A does not directly neutralize LPS effectively in vitro, and studies reported to date have not defined its mechanism of action. Here we demonstrate that HA-1A, which in the presence of complement promotes immune adherence, may inhibit LPS action by facilitating its sequestration on red blood cells and clearance to an extent that cytokine production is reduced. Incubation of LPS at clinically significant (pg/ml) does with HA-1A at therapeutic levels (e.g. 10 micrograms/ml) and complement resulted in LPS association with erythrocyte CR1 receptors. This reduced the ability of the residual, free LPS by 50-70% to induce the secretion of TNF-alpha, IL-1 beta and IL-6 from normal blood mononuclear cells. This mechanism is likely to be operative in vivo, and could account for the protective effect of HA-1A, and its reduction of TNF-alpha production in vivo.

Antibodies, Monoclonal↗
PubMed1993

Brain purines in a genetic mouse model of Lesch-Nyhan disease.

Mice carrying a mutation in the gene encoding the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) have recently been produced to provide an animal model for Lesch-Nyhan disease. The current studies were conducted to characterize the consequences of the mutation on the expression of HPRT and to characterize potential changes in brain purine content in these mutants. Our results indicate that the mutant animals have no detectable HPRT-immunoreactive material on western blots and no detectable HPRT enzyme activity in brain tissue homogenates, confirming that they are completely HPRT deficient (HPRT-). Despite the absence of HPRT-mediated purine salvage, the animals have apparently normal brain purine content. However, de novo purine synthesis, as measured by [14C]formate incorporation into brain purines, is accelerated four- to fivefold in the mutant animals. This increase in the synthesis of purines may protect the HPRT- mice from potential depletion of brain purines despite complete impairment of HPRT-mediated purine salvage.

Adenine Nucleotides↗
PubMed1992

Acute effect of benfluorex on glucose metabolism.

The antihyperlipidaemic agent benfluorex [1-(3-trifluoromethylphenyl)-2-(2-benzoyl-oxyethyl)-aminopropane] and its metabolite S422 [1-(3-trifluoromethylphenyl)-2-(2-hydroxyethyl)-aminopropane] were examined for an acute (after 1-2 hr) effect on glucose metabolism in normal rats. Enteral administration of benfluorex (25 mg/kg) did not affect basal plasma glucose and insulin concentrations. However, enteral and intravenous glucose tolerance were modestly improved without enhancing the insulin response to glucose. Hepatic gluconeogenesis from lactate was not acutely altered by benfluorex (25 mg/kg) in vivo or by S422 (1 mM) in vitro, but S422 (1 mM) slightly reduced (by 11%) hepatic glycogen mobilization in vitro after 2 hr. S422 (1 mM) increased (by 47%) glucose oxidation by diaphragm muscle in vitro. The effect was additive to that of insulin. Anaerobic glucose metabolism and glycogenesis of diaphragm muscle were not affected by S422. The results suggest that benfluorex can acutely improve glucose tolerance associated with increased glucose oxidation by muscle.

Animals↗
PubMed1992

Characterization of mutations in phenotypic variants of hypoxanthine phosphoribosyltransferase deficiency.

The Lesch-Nyhan disease is caused by an almost complete lack of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). Partial HPRT-deficiency, associated with less severe phenotype, has also been identified. We have characterized mutations occurring in HPRT cDNA isolated from patients with HPRT-deficiency with an emphasis on examining the more unusual partial variants of HPRT-deficiency. HPRT cDNA was amplified by PCR, cloned and analyzed by automated DNA sequence analysis. Twenty-two, unrelated individuals with HPRT deficiency were studied including eight classic Lesch-Nyhan patients and fourteen patients representing the different groups of partial HPRT deficiency. We found a diverse pattern of mutations with point mutations accounting for the majority of abnormal HPRT genes. Nonsense mutations and exon deletions were only found in HPRT cDNA isolated from classic Lesch-Nyhan patients. Mutations associated with partial HPRT-deficiency were frequently located in the amino terminal part of the molecule. A CpG mutational hot spot was identified at the position for Arg-51 in the HPRT protein. Two hyperuricemic patients exhibited unusual splice site mutations: in one this led to the creation of an additional exon in the HPRT gene and in the other part of exon 6 was missing in a subpopulation of the transcripts, producing the effect of a dominant, negative mutation.

Amino Acid Sequence↗
PubMed1990

A pitfall in the prenatal diagnosis of Lesch-Nyhan syndrome by chorionic villus sampling.

The ratio of the activities of catabolic enzymes such as 5'-nucleotidase and purine nucleoside phosphorylase to that of hypoxanthine-guanine phosphoribosyltransferase (HPRT) may be much higher in frozen or cultured chorionic villus cells than in cultured amniotic fluid cells, cultured fibroblasts, or red blood cells. Consequently, unless these catabolic activities are controlled the observed activity of HPRT may be greatly decreased, and a false diagnosis of Lesch-Nyhan syndrome may result. For a reliable diagnosis, the reaction products of HPRT must be protected from catabolism.

Adenine Phosphoribosyltransferase↗