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Biomedical subjects

D B Dickinson

Publications and source records attributed to D B Dickinson.

At least 19 recordsLinked to original sources
PubMed2006

Effects of HIV-related stigma among an early sample of patients receiving antiretroviral therapy in Botswana.

Botswana, with its estimated HIV prevalence of 37%, instituted a policy of universal access to antiretroviral therapy (ART) in 2002. Initial enrolment lagged behind expectations, with a shortfall in voluntary testing that observers have attributed to HIV-related stigma - although there are no published data on stigma among HIV-positive individuals in Botswana. We interviewed 112 patients receiving ART in 2000, finding evidence of pervasive stigma in patterns of disclosure, social sequelae, and delays in HIV testing. Ninety-four percent of patients reported keeping their HIV status secret from their community, while 69% withheld this information even from their family. Twenty-seven percent of patients said that they feared loss of employment as a result of their HIV status. Forty percent of patients reported that they delayed getting tested for HIV; of these, 51% cited fear of a positive test result as the primary reason for delay in seeking treatment, which was often due to HIV-related stigma. These findings suggest that success of large-scale national ART programmes will require initiatives targeting stigma and its social, economic and political correlates.

Adult↗
PubMed1992

Reduction of phytic acid in soybean products improves zinc bioavailability in rats.

The inhibitory effect of phytic acid in soybean products on zinc bioavailability was evaluated in two experiments in rats. In Experiment 1, soybean flours containing different natural phytic acid levels produced by sand culture techniques that limited phosphorus during growth of the soybean plants were formulated into diets. The rats fed a higher phytic acid level diet had lower food intake, depressed weight gain, and lower tibia zinc gain (P < 0.05). A negative, linear relationship between tibia zinc gain and dietary phytic acid level was found. In Experiment 2, two commercially produced soybean isolates containing either normal phytic acid level or a reduced level were formulated into diets. Slope ratio analysis revealed that relative zinc bioavailability from phytic acid-containing soybean isolate-based diets was significantly reduced (P < 0.05) compared with control diets. Reduced phytic acid soybean isolate-containing diets resulted in a significant increase of zinc bioavailability compared with normal phytic acid diets (P < 0.01). These results coupled with other reports indicate that phytic acid is the primary inhibitory factor in soybean products that results in reduced zinc bioavailability and that phytate reduction in soybean protein increases zinc bioavailability.

Animals↗
PubMed1987

Phytic Acid Metabolism in Lily (Lilium longiflorum Thunb.) Pollen.

The accumulation of phytic acid during development of lily (Lilium longiflorum Thunb.) pollen and its degradation during germination have been studied. A substantial amount of phytic acid accumulates in lily pollen by 5 days before anthesis, and little change occurs during subsequent maturation. Mature lily pollen contains 7 to 8 micrograms phytic acid per milligram pollen. Considerable degradation of phytic acid occurs by 15 minutes of incubation in glucose culture medium, and very little is left by 3 hours. No partially phosphorylated myo-inositol accumulates during germination. The breakdown of phytic acid proceeds at a constant rate during this time period. The rate is calculated to be 0.037 microgram phytic acid/milligram pollen/minute. Two phytases are detected in germinated lily pollen extract using high performance liquid chromatography with an anion exchange column (diethylaminoethyl-5PW). The results suggest that one of the phytases is already present in mature ungerminated lily pollen and the other one is newly synthesized during germination from a long-lived, pre-existing mRNA.

Journal Article↗
PubMed1987

The timing and rate of phytic Acid accumulation in developing soybean seeds.

The time-course of phosphorus (P) accumulation in the phytic acid fraction of developing soybean (Glycine max [L.] Merr. cv ;Williams 79') seeds as well as the relation of phytic acid P to total P content were determined. Phytic acid was detected early in embryogenesis in field-grown soybeans and accumulated in a linear fashion throughout most of seed development. Although the observed rates of accumulation ranged from 18.7 micrograms phytic acid P per seed per day in pods positioned low on the plant to 33.6 micrograms in pods positioned high on the plant, the final concentrations were the same in all cases. Nearly all of the P translocated to developing seeds was incorporated into phytic acid from the third week after flowering until physiological maturity, with the sum of nonphytic acid P compounds remaining constant. Phytic acid accumulation was also linear throughout development when soybean plants were grown in solutions having nutrient P levels that ranged from severely limiting (2.0 milligrams P per liter) to excess (50 milligrams P per liter). However, there was a pronounced effect on rate of accumulation, which ranged from 7.2 micrograms phytic acid per seed per day with limiting nutrient P to 44.7 micrograms with excess P. The change in level of phytic acid accounted for most of the alteration in total seed P that was caused by altering the P status of the plants. These results support the view that phytic acid synthesis is involved in P homeostasis of the developing soybean seed.

Journal Article↗
PubMed1984

Ability of Pollen to Germinate prior to Anthesis and Effect of Desiccation on Germination.

The ability of pollen to germinate prior to anthesis was tested using Easter lily (Lilium longiflorum L.) and corn (Zea mays L.). Lily pollen normally dries to a low moisture content between anthesis and pollination while corn does not. The corn pollen germinated well (about 73%) when removed from anthers 1 day before anthesis and placed on culture medium. The lily pollen germinated poorly (0 to 5%) when harvested one to six days before anthesis. However, the lily pollen harvested one or two days before anthesis gave greatly improved germination (about 55%) after it was dried to a low moisture content. The results indicate that an internal control prevents premature germination of lily pollen and that drying is the final stage of pollen maturation. A different sort of regulatory mechanism must operate to prevent premature germination of corn pollen.

Journal Article↗
PubMed1984

Studies of sugars and sorbitol in developing corn kernels.

Sugars and sorbitol were determined on corn (Zea mays L.) kernels harvested at various developmental stages, using sugary (su), sugary-sugary enhancer (su se), and starchy (Su) cultivars. In all cultivars tested, the sorbitol content increased from trace amounts in unpollinated ovules to a maximum at about the time that rapid starch synthesis was proceeding. Thereafter, sorbitol and sugars decreased continuously to the mature dry stage. Sorbitol in the su se kernels was higher than that of other cultivars from 28 days postpollination onwards; sucrose and maltose were higher from 21 days onwards. [(14)C]Sorbitol was recovered from kernel base, pedicel, and endosperm of IL677a (su se) kernels after allowing a flag leaf to fix (14)CO(2) photosynthetically. No [(14)C]sorbitol was detected in the shank of the ear, and none was detected by the gas chromatograph. [(14)C]Sucrose was the predominant labeled substance recovered from the kernel base, pedicel, and endosperm tissues during the 10-h chase period, as well as from the shank of the ear, and nonradioactive sucrose was the predominant ethanol-soluble compound detected by the gas chromatograph. Hence, sorbitol appears not to be translocated from corn leaves as it is in certain woody plants of the rose family. The altered sugar profile of su se kernels may be related to reduced starch synthesis, but the biochemical mechanism is not yet known.

Journal Article↗
PubMed1984

Effect of phosphorus and zinc nutrition on soybean seed phytic Acid and zinc.

The relationships between nutrient P and Zn levels and the phytic acid, P, and Zn concentrations in soybean (Glycine max L. Merr. cv ;Williams 79') seed were studied. Phytic acid increased linearly from 4.2 to 19.2 milligrams per gram as nutrient P treatment was varied from 2.0 to 50 milligrams per liter and Zn was held constant at 0.05 milligrams per liter. Leaf P concentration during seed development was found to be closely related to the concentrations of seed P and phytic acid. Leaf and seed Zn concentrations both responded positively to increasing nutrient Zn treatment. The effects of P treatment on plant and seed P and phytic acid were largely independent of the effects of Zn treatment on leaf and seed Zn. Phytic acid to Zn molar ratios ranging from 3.6 to 33.8 were observed.The effects of nutrient P treatments on the concentrations of phytic acid, seed P, and leaf P were also studied in the P-sensitive (gene np) cultivars ;Harosoy' and ;Clark' and their respective P-tolerant (gene Np) near-isogenic lines L66-704 and L63-1677. In general, the positive relationships observed among nutrient P, leaf P, seed P, and phytic acid concentrations were similar to those observed in the studies with Williams 79. When fertilized with low or moderate nutrient P (2.5 and 25.0 milligrams P per liter, respectively) no significant differences in any parameter were observed between Harosoy or Clark and their respective P-tolerant isolines. When fertilized with high nutrient P (100 milligrams P per liter), Harosoy seed had a significantly higher concentration of phytic acid (30 milligrams per gram) than did seed of its P-tolerant near-isogenic line L66-704 (24.2 milligrams per gram phytic acid), whereas no significant difference was observed between Clark and its P-tolerant near-isogenic line L63-1677 (22.8 and 21.6 milligrams per gram, respectively). Variation in the phytic acid concentrations in the mature seed of the cultivars and isolines more closely paralleled leaf P concentrations observed during seed development (49 days after flowering), than those observed at the onset of seed development (14 days after flowering). Electrophoresis and ion-exchange chromatography revealed that partially phosphorylated intermediates do not appear when phytic acid accumulation is greatly reduced by limiting the nutrient P or when accumulation is greatly accelerated by excess P.

Journal Article↗
PubMed1979

Antigen E content of pollen from individual plants of short ragweed (Ambrosia artemisiifolia).

A study was conducted to ascertain how much variation in allergenic potency of ragweed pollen occurs among individual plants and different plant populations in a restricted geographic area. Seeds of the short ragweed (Ambrosia artemisiifolia) were collected from 38 different sites in Champaign County, Ill. Plants from these seeds were grown under similar conditions, and antigen E (AgE) was determined on pollen samples harvested from individual plants. The populations from various sites in Champaign County differed by as much as severalfold with respect to mean AgE values. There were statistically significant differences among population means, although large variations occurred among plants within populations. Further research was conducted to learn whether the level of AgE was determined by genetic factors within the plants. Genetic regulation was indicated by the finding that 3 plants which had unusually low levels of pollen AgE all produced offspring with significantly lower mean AgE levels than those of control plants.

Antigens↗
PubMed1979

Analysis of Endosperm Sugars in a Sweet Corn Inbred (Illinois 677a) Which Contains the Sugary Enhancer (se) Gene and Comparison of se with Other Corn Genotypes.

The endosperm sugars of a new corn (Zea mays L.) mutant, sugary enhancer (se), were analyzed by gas-liquid chromatography and were compared with sugars of other genotypes. Illinois 677a, a sugary (su) inbred containing the se gene, was high in sucrose and was distinguished from all of the other genotypes by its high maltose content. During kernel development, the maltose content of IL677a increased to 3.28% dry weight at 40 days postpollination and remained high at the dry mature stage, whereas ;Silver Queen,' a high quality sugary (su) hybrid not possessing the se gene, showed no such trend in maltose accumulation. Sucrose, fructose, and glucose decreased during kernel development in ;Silver Queen' and IL677a from 19 days postpollination until the dry mature stage. The slow drying characteristic and the reduced starch content previously reported for maturing seeds of IL677a may be related to the maltose accumulation reported here.

Journal Article↗
PubMed1978

Metabolism of myo-Inositol by Germinating Lilium longiflorum Pollen.

Lilium Iongiflorum pollen tubes absorbed myo-[2-(3)H]inositol produced labeled metabolites which were separated into acid-soluble and -insoluble fractions. The soluble fraction contained labeled myo-inositol, d-glucuronic acid, myo-inositol 1-phosphate, and at least three other unidentified compounds. The acid-insoluble fraction contained considerable chloroformsoluble radioactivity and a labeled residue. Labeled myo-inositol was also absorbed by germinating pollen prior to the time of pollen tube initiation; however, there was a marked reduction in amounts of myo-inositol 1-phosphate and glucuronic acid produced by this pollen in comparison with growing pollen tubes.

Journal Article↗
PubMed1978

Inhibition of glucuronokinase by substrate analogs.

Glucuronokinase from Lilium longiflorum pollen was purified 30- to 40- fold on a blue dextran-Sepharose column. Substrate analogs were tested for inhibitory effects, and nucleotide substrate specificity of the enzyme was determined. Nine nucleotides were tested, and all were inhibitory when the substrate was ATP. ADP was competitive with ATP and had a K(i) value of 0.23 mm. None of the other nucleotide triphosphates could effectively substitute for ATP as a nucleotide substrate. Ten mm dATP and ITP reacted only 3% as rapidly as 10 mm ATP, while the rates for 10 mm GTP, CTP, UTP, and TTP were less than 1%. The glucuronic acid analogs, methyl alpha-glucuronoside, methyl beta-glucuronoside, beta-glucuronic acid-1-phosphate, and 4-O-methylglucuronic acid were tested as possible enzyme inhibitors. The three methyl derivatives showed little or no inhibition. The beta-glucuronic acid-1-phosphate was inhibitory, with 50% inhibition obtained at 1 to 3 mm depending on the concentration of the glucuronic acid. It is concluded that the glucuronic acid-binding site on the enzyme is highly selective.

Journal Article↗
PubMed1977

Isolation of uridine 5'-pyrophosphate glucuronic Acid pyrophosphorylase and its assay using p-pyrophosphate.

A procedure was devised to detect and assay uridine 5'-pyrophosphate (UDP)-glucuronic acid pyrophosphorylase in plant extracts. Substrates are UDP-glucuronic acid and (32)P-pyrophosphate, and the (32)P-uridine 5'-triphosphate produced is selectively adsorbed to charcoal. The charcoal adsorption procedure is a modification of that used to determine (32)P-adenosine 5'-triphosphate produced by adenosine 5'-pyrophosphate glucose pyrophosphorylase, and the modification greatly improves the retention of uridine 5'-triphosphate.

Journal Article↗
PubMed1976

Carbohydrate and enzymic characterization of a high sucrose sugary inbred line of sweet corn.

Reserve carbohydrates were determined on developing endosperm of a new line of sugary maize (Zea mays L.). Other entries, included for comparative purposes, were Midway (sugary), Funks G4646 (starchy), and Illini X-tra Sweet (shrunken-2). Sucrose in the new line, Illinois 677a, was more than twice that of Midway at most stages of development, and reached a maximum of 40% of dry weight at 18 days after pollination. Appreciable phytoglycogen accumulated in Illinois 677a, reaching 30% or more of dry weight as endosperm tissue matured. Thus, Illinois 677a is a typical sugary maize concerning phytoglycogen content, but it resembles shrunken-2 concerning the extent of sucrose accumulation.Enhanced sucrose accumulation by Illinois 677a was not accounted for by altered in vitro activities of invertase, sucrose synthase, UDP-glucose pyrophosphorylase, or ADP-glucose pyrophosphorylase. Its normal level of ADP-glucose pyrophosphorylase set Illinois 677a apart from shrunken-2 in which the enzyme was drastically reduced.

Journal Article↗
PubMed1975

beta-1, 3-Glucan Synthase from Lilium longiflorum Pollen.

A particulate fraction from pollen tubes and ungerminated pollen of Lilium longiflorum incorporated (14)C-glucose from UDP-glucose-(14)C into a lipid fraction and into beta-1, 3-glucan. Partial hydrolysis of the glucan yielded laminaribiose as the only radioactive disaccharide. The preferred substrate was UDP-glucose, and enzyme activity was stimulated by glucose and by beta-linked di- and trisaccharides. Enzyme from growing pollen tubes synthesized beta-1, 3-glucan more rapidly and produced a higher proportion of alkali-insoluble glucan than did enzyme from ungerminated pollen. The onset of pollen tube growth may be dependent on altered activity of beta-1, 3-glucan synthase.

Journal Article↗