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Biomedical subjects

D J Robison

Publications and source records attributed to D J Robison.

10 recordsLinked to original sources
PubMed2001

Genotypic effects of fertilization on seedling sweetgum biomass allocation, N uptake, and N use efficiency.

Screening and selecting tree genotypes that are responsive to N additions and that have high nutrient use efficiencies can provide better genetic material for short-rotation plantation establishment. A pot experiment was conducted to test the hypotheses that (1) sweetgum ( Liquidambar styraciflua L.) families have different patterns in biomass production and allocation, N uptake, and N use efficiency (NUE), because of their differences in growth strategies, and (2) sweetgum families that are more responsive to N additions will also have greater nutrient use efficiencies. Seedlings from two half-sib families (F10022 and F10023) that were known to have contrasting responses to fertility and other stress treatments were used for an experiment with two levels of N (0 vs. 100 kg N/ha equivalent) and two levels of P (0 vs. 50 kg P/ha equivalent) in a split-plot design. Sweetgum seedlings responded to N and P treatments rapidly, with increases in both size and biomass production, and those responses were greater with F10023 than with F10022. Growth response to N application was particularly strong. N and P application increased the proportional allocation of biomass to leaves. Under increased N supply, P application increased foliar N concentration and content, as well as total N uptake by the seedlings. However, NUE was decreased by N addition and was higher in F10023 than in F10022 when P was not limiting. A better understanding of genotype by fertility interactions is important in selecting genotypes for specific site conditions and for optimizing nutrient use in forestry production.

Biomass↗
PubMed1994

Polyethylene-starch extrudates as erodible carriers for bioactive materials: I. Erodibility and in vitro dye release studies.

The objective of the present investigation is to develop and evaluate polyethylene-starch based carriers for sustaining the release of bioactive materials. Polyethylene-starch carriers were prepared by incorporating various amounts of corn starch 0, 40, 80, and 100% in polyethylene beads with and without dye. Acid orange dye was incorporated (1%) to study release patterns and the effect of starch (%) on release. The granulated mixtures were extruded to form uniform dispersions of starch and polyethylene throughout the extrudate. The extrudates obtained were studied for SEM surface characterization before, during, and after release studies to study the erosion process. In the case of 100% starch, 80% of the matrix was eroded in 5 weeks, while with 40% and 80% starch, erosion was less than 20%. The dye release studies showed that release could be sustained well over 12 weeks, depending on the starch (%) incorporated. The erosion process was studied using scanning electron microscopic techniques, which showed gradual erosion of starch particles, leaving a polyethylene skeleton. These materials show promising potential for use as carriers for bioactive materials.

Coloring Agents↗
PubMed1993

HIV-1 antibody serum negativity with urine positivity.

7 individuals who were negative for HIV-1 antibody in a licensed serum enzyme immunoassay (EIA) were positive in a urine EIA and western blot (WB). Follow-up in individuals by use of a cell-mediated immune response showed 1 positive and 1 negative for HIV-1 peptide reactivity. In a second study, 4 out of 5 subjects positive by urine EIA and indeterminate or negative by serum WB were HIV-1 peptide positive in the cell-mediated immune test. Comparison of cell-mediated responses with urine antibody responses may help to resolve discrepant HIV-1 results.

Adolescent↗
PubMed1982

Computer-generated models of blood coagulation factor Xa, factor IXa, and thrombin based upon structural homology with other serine proteases.

Computer-generated molecular models of the trypsin-like domains of blood coagulation factor IXa, Factor Xa, and thrombin have been prepared. These hypothetical models are based upon the sequence homology of the blood coagulation enzymes with the pancreatic serine proteases and the known three-dimensional structure of the pancreatic serine proteases. The internal structures and active sites of these enzymes are highly conserved. The high degree of substrate specificity which characterizes the blood coagulation enzymes appears to be defined not entirely by the active site, but by the unique molecular surface surrounding the active site of each enzyme. Several regions which demonstrate high sequence variability among these enzymes likely participate in forming the putative extended substrate binding sites.

Amino Acid Sequence↗
PubMed1981

A computer-generated three-dimensional model of the B chain of bovine alpha-thrombin.

A computer graphic molecular display system has been used to construct a three-dimensional model of the B chain of bovine thrombin. The model is derived from the bovine alpha-chymotrypsin structure as determined by X-ray crystallographic studies. The amino acid sequence of bovine thrombin has been substituted for that of alpha-chymotrypsin, preserving the beta-barrel structure and maximizing homology of the amino acid sequence of the two proteins. With the exception of an area in the vicinity of the specificity binding pocket, most of the changes observed in thrombin occur on the surface of the molecule. The most notable changes observed in the model are the increases on the surface of positively charged (arginine and lysine) and negatively charged (glutamate and aspartate) residues. A glutamate replaces methionine 192 near the entrance to the specificity binding pocket. The nature of this site was further altered by the substitution of an aspartate for serine 189 and an alanine for serine 190. The structure of the resulting specificity binding pocket is consistent with that of serine proteases, which have trypsin-like substrate specificity. The computer graphics molecular display system has been used to insert models of synthetic thrombin inhibitors into the active site of the thrombin B chain model. With the model, it has been possible to correlate the interaction of thrombin with the observed binding constants of two inhibitors of trypsin-like serine proteases, p-amidinophenylmethylsulfonylfluoride (Ki = 1.27 x 10(-6) M) and m-[m-(trifluoromethyl)phenoxypropoxy]benzamidine (KD = 2.9 x 10(-6) M).

Amino Acids↗
PubMed1980

(p-Amidinophenyl)methanesulfonyl fluoride, an irreversible inhibitor of serine proteases.

p-(Amidinophenyl)methanesulfonyl fluoride (p-APMSF) has been synthesized and shown to be a specific, irreversible inhibitor of the class of plasma serine proteases which demonstrate substrate specificity for the positively charged side chains of the amino acid lysine or arginine. In equimolar concentration, this compound causes immediate and complete irreversible inhibition of bovine trypsin and human thrombin. A 5-10-fold molar excess of reagent over enzyme is required to achieve complete irreversible inhibition of bovine Factor Xa, human plasmin, human C1-r, and human C1-s. the Ki of p-APMSF for all of the above-mentioned proteases is between 1 and 2 microM. In contrast, p-APMSF in large molar excess does not inactivate chymotrypsin or acetylcholinesterase. The unique reactivity of p-APMSF has been further shown in comparison with the related compound p-nitrophenyl (p-amidinophenyl)methanesulfonate which is an active-site titrant for thrombin but reacts poorly with Factor Xa, C1-r, and C1-s and is not hydrolyzed by bovine trypsin or human plasmin. Similarly, (p-amidinophenyl)methanesulfonate has a Ki of 30 microM for thrombin but is a poor inhibitor of trypsin, Factor Xa, C1-r, C1-s, and plasmin. Studies with bovine trypsin have demonstrated that the inhibitory activity of p-APMSF is the result of its interaction with the diisopropyl fluorophosphate reactive site. The unique reactivity of this inhibitor classifies it as one of the most effective active site directed reagents for this class of serine proteases. Collectively, these results suggest that the primary substrate binding site of these enzymes, which share a high degree of structural homology, do in fact significantly differ from each other in their ability to interact with low molecular weight inhibitors and synthetic substrates.

Models, Molecular↗
PubMedDate not supplied

Pyogenic liver abscess.

Experience with 34 patients with pyogenic liver abscess is reviewed to evaluate the impact of percutaneous drainage and duration of antibiotic therapy on results of treatment. Patients with shock, adult respiratory distress syndrome, disseminated intravascular coagulation, jaundice, severe hypoalbuminemia, and diabetes had a poor prognosis. Percutaneous drainage was used successfully in 4 of 6 patients, but its use did not affect mortality rate or length of hospital stay. Percutaneous drainage may be the procedure of choice for selected patients. Half of our patients received antibiotics for 2 weeks or less with no abscess recurrences in this group. Long-term antibiotics may not be necessary after adequate surgical or percutaneous abscess drainage.

Adolescent↗