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Biomedical subjects

D L Smith

Publications and source records attributed to D L Smith.

At least 199 records · Page 11Linked to original sources
PubMed1994

Asimin, asiminacin, and asiminecin: novel highly cytotoxic asimicin isomers from Asimina triloba.

Activity-directed fractionation of the stem bark extracts of the North American paw paw tree, Asimina triloba (Annonaceae), has yielded three further acetogenins: asimin (2), asiminacin (3), and asiminecin (4). 2-4 are structural isomers of asimicin (1), which is a potent inhibitor of mitochondrial NADH:ubiquinone oxidoreductase, and thus exhibits potent antitumor and pesticidal effects. 2-4 have the same carbon skeleton and configurations as those of 1, but they have the third hydroxyl group located at C-10, C-28, and C-29, respectively, rather than at C-4. The determinations of the hydroxyl group locations were largely based on mass spectral analyses of TMSi and TMSi-d9 derivatives. 2-4 all showed highly potent cytotoxicities (ED50 values as low as < 10(-12) micrograms/mL) with notable selectivities for the HT-29 human colon cancer cell line. The presence of a third hydroxyl at C-4, C-10, C-28, or C-29, as in 1-4, greatly enhances the bioactivity of 4-deoxyasimicin (5).

Antineoplastic Agents, Phytogenic↗
PubMed1994

Allergy and immunology.

An apparent epidemic of fatal asthma has occurred despite ever-increasing expenditures for asthma medications. Atopy is the genetic predisposition toward responses that result in the formation of large quantities of allergen-specific IgE. Biotechnology has made it possible to manufacture proteins that regulate immune responses.

Allergy and Immunology↗
PubMed1994

Operator-constitutive mutations in a DNA sequence recognized by a yeast homeodomain.

Homeodomain proteins regulate transcription in organisms as diverse as yeasts, mammals and plants, often effecting key decisions in development. Although homeodomains can selectively recognize certain DNA sequences, a question has arisen as to how specific this interaction is and how much it contributes to the ability of these proteins to properly select target genes in the cell. This question is particularly an issue in cases where the homeodomain proteins recognize DNA cooperatively with other DNA-binding proteins. In this paper, we examine the issue of DNA binding specificity for the homeodomain of the yeast alpha 2 protein (which recognizes the a-specific gene operator cooperatively with the MCM1 protein) by examining both in vivo and in vitro the effects of point mutations in its recognition sequence. We found that most changes in the homeodomain recognition sequence produced only small effects on both homeodomain affinity as measured in vitro (with and without the helper protein MCM1) and operator function as determined in vivo. This tolerance for operator mutations illustrates in a systematic way the modest DNA-binding specificity of the alpha 2 homeodomain and contrasts with the behavior of many of the bacterial and phage repressors where single point mutations in the operator can have dramatic effects on affinity. This tolerance for different sequences may arise from the fact that most of the interactions made between the alpha 2 homeodomain and the DNA occur through long amino acid side chains; we suggest that these side chains can reconfigure in order to create surfaces complementary to many different DNA sequences. The relaxed DNA-binding specificity of homeodomain proteins such as alpha 2 may be an important feature that permits new regulatory circuits to evolve rapidly from existing components.

Base Sequence↗
PubMed1994

Post-translational modifications of water-soluble human lens crystallins from young adults.

Post-translational modifications of the water-soluble human lens crystallins from young adult donors were identified and located using electrospray ionization mass spectrometric analysis of the intact proteins and fast atom bombardment mass spectrometry of enzymatic digests. Peptides corresponding to all of the sequences of alpha A-, alpha B-, and beta B2-crystallins were found, permitting the entire sequences to be searched for modifications. The major portions of these three crystallins were not modified. Modifications of alpha A-crystallin that were detected included 2 phosphorylated Ser residues (1 of which appears to be unique to human lenses), deamidation at some Gln and Asn residues, a disulfide bond between Cys-131 and Cys-142, and loss of the COOH-terminal Ser residue. Three phosphorylated Ser residues, but no deamidation, were found in alpha B-crystallin. The molecular weights of neither the intact protein nor the peptides in the enzymatic digests indicated any post-translational modification of the principal beta-crystallin, beta B2. The molecular weights of the other beta- and gamma-crystallins for which sequences have been published suggested the presence of post-translational modifications or errors in the published sequences. Although enough peptides were found to establish the presence of specific proteins, peptides corresponding to all portions of these proteins were not found, and elucidation of these structures is not yet complete. This mass spectrometric characterization of the total water-soluble proteins from normal young adult lenses provides a reference data base for future investigations of the modifications present in aged and cataractous lenses.

Adult↗
PubMed1994

Identification of cyclic AMP response element in the human renin gene.

In order to identify the mechanism by which cyclic AMP stimulates expression of the human renin gene (REN), the effect of forskolin was tested in transient expression analyses of REN 5'-flanking DNA-chloramphenicol acetyltransferase (CAT) reporter gene constructs in secondary cultures of human chorio-decidual cells, a major site of renin synthesis. Forskolin induced a mean 5-fold stimulation which was localized to DNA in the region -249 to -162 with respect to the transcription start site (+1). Such DNA also mediated a response to forskolin in heterologous (HSV thymidine kinase) promoter constructs. Strong cAMP-response element (CRE) homology at -222 to -218 resembled the target for members of the CRE binding protein (CREB) family. Gel shift assays demonstrated similarly migrating nucleoprotein complexes for oligonucleotides containing the putative REN CRE as for a canonical CRE, in chorio-decidual, JEG-3 and HeLa nuclear extracts. Mutation of residues critical for CREB attachment reduced binding. In conclusion, a CRE was identified at -222 to -218 that appears critical for cAMP-induced human renin gene transcription.

Animals↗
PubMed1994

The structure and function of surfactant protein A. Hydroxyproline- and carbohydrate-deficient mutant proteins.

Pulmonary surfactant protein A (SP-A) regulates the uptake and secretion of phospholipid by alveolar type II cells and is an important component of surfactant lipid aggregates. In an attempt to understand how specific structural domains of SP-A relate to the function of the protein, we used site-directed mutagenesis of the cDNA for SP-A and heterologous expression with baculovirus vectors. Synthesis of the wild type SP-A in insect cells resulted in a form of the protein in which proline residues were not hydroxylated and that is denoted SP-Ahyp. Three mutant SP-As with substitutions in the consensus sequences for glycosylation (SP-Ahyp,glc) to prevent N-linked oligosaccharide attachment at Asn1 and Asn187 were produced, individually and in tandem. The SP-Ahyp was glycosylated at both the Asn1 and Asn187 positions, demonstrated partial sulfhydryl-dependent oligomerization, and formed incomplete oligomers in solution. The SP-Ahyp and SP-Ahyp,glc bound to immobilized carbohydrate and to phospholipid liposomes and partially competed for occupancy of a plasma-membrane receptor for SP-A. The SP-Ahyp and the SP-Ahyp,glc were equally effective inhibitors of the secretion of surfactant lipids from isolated type II cells (IC50 = 0.5 microgram/ml) and aggregated phospholipid liposomes at 20 degrees C. All of the recombinant SP-As demonstrated markedly reduced aggregation of lipid at 37 degrees C. We conclude that the hydroxylation of proline residues is required for perfect oligomerization of SP-A and for thermal stability in the interaction with lipid. Furthermore, recombinant SP-A is able to inhibit the secretion of phospholipid from isolated type II cells and to aggregate lipid vesicles independent of the presence of N-linked carbohydrate or the site of glycosylation.

Animals↗
PubMed1994

Pyoderma gangrenosum in association with psoriatic arthritis.

We present a patient with psoriasis and psoriatic arthritis who developed multiple large, painful ulcers that were scattered over his anterior lower legs and were characteristic of pyoderma gangrenosum (PG). This association has not previously been described. We review other forms of arthritis that usually occur with PG and discuss them in light of this observation.

Arthritis, Psoriatic↗
PubMed1994

DNA markers associated with high versus low IQ: the IQ Quantitative Trait Loci (QTL) Project.

General cognitive ability (intelligence, often indexed by IQ scores) is one of the most highly heritable behavioral dimensions. In an attempt to identify some of the many genes (quantitative trait loci; QTL) responsible for the substantial heritability of this quantitative trait, the IQ QTL Project uses an allelic association strategy. Allelic frequencies are compared for the high and low extremes of the IQ dimension using DNA markers in or near genes that are likely to be relevant to neural functioning. Permanent cell lines have been established for low-IQ (mean IQ = 82; N = 18), middle-IQ (mean IQ = 105; N = 21), and high-IQ (mean IQ = 130; N = 24) groups and for a replication sample consisting of even more extreme low-IQ (mean IQ = 59; N = 17) and high-IQ (mean IQ = 142; N = 27) groups. Subjects are Caucasian children tested from 6 to 12 years of age. This first report of the IQ QTL Project presents allelic association results for 46 two-allele markers and for 26 comparisons for 14 multiple-allele markers. Two markers yielded significant (p < .01) allelic frequency differences between the high- and the low-IQ groups in the combined sample-a new HLA marker for a gene unique to the human species and a new brain-expressed triplet repeat marker (CTGB33). The prospects for harnessing the power of molecular genetic techniques to identify QTL for quantitative dimensions of human behavior are discussed.

Alleles↗
PubMed1994

The volatiles of desert truffle: Tirmania nivea.

The volatile constituents of Tirmania nivea (white desert truffle) have been analysed, using gas chromatography/mass spectrometric technique. 11 compounds have been identified in the ascocarp volatiles. The major components were found to be unsaturated fatty acids; whereas hexadecanoic [correction of haxadecanoic] acid represented 49% of the volatiles isolate.

Ascomycota↗
PubMed1994

Microwave thermal balloon angioplasty in the atherosclerotic rabbit.

We evaluated the angiographic and histologic response of the coronary vessels of the atherosclerotic rabbit to microwave thermal balloon angioplasty. Sixteen rabbits with atherosclerosis of the external iliac arteries following a high fat diet and endothelial denudation were treated with either CBA or MBA. Four weeks following angioplasty angiography was repeated, and following the death of the animals, the vessels treated were excised for histologic evaluation. In vessels with MBA with peak temperatures of 85 degrees C there was an increase in luminal diameter immediately postangioplasty, from 1.66 +/- 0.32 mm to 2.54 +/- 0.23 mm (p < 0.05). The diameter at 4 weeks (2.29 +/- 0.74 mm) remained increased compared with the preangioplasty diameter (p < 0.05). With microwave angioplasty at 70 degrees C there was an increase in luminal diameter, from 1.92 +/- 0.37 mm to 2.40 +/- 0.22 mm (p < 0.05) immediately postangioplasty. This increase in diameter was not sustained at 4 weeks (1.86 +/- 0.28 mm). In the vessels treated with CBA there was no significant increase in diameter noted either immediately postangioplasty or at 4 weeks postangioplasty. In the thermally treated vessels, histologic evaluation revealed a loss of lipid-laden cells; it also revealed the formation of a concentric hypocellular fibrotic layer. Microwave thermal balloon angioplasty at 85 degrees C results in enhancement of the immediate and delayed response to angioplasty. Modification of the proliferative response to angioplasty may be accomplished with this modality.

Angioplasty, Balloon↗
PubMed1994

Olecranon and pretibial bursitis in atopic dermatitis: coincidence or association?

BACKGROUND: Bursal fluid accumulations are not usually associated with skin disease; however, several cases have been observed in a large atopic dermatitis (AD) clinic. OBJECTIVE: We sought to characterize the clinical features of bursitis in AD and to assess the evidence for a mechanistic association between these conditions. METHODS: We retrospectively evaluated the clinical presentation of bursitis in six adults with lifelong severe AD. The course of the bursitis and possible causative factors were assessed for each patient. RESULTS: Ten episodes of bursitis were documented in six patients with chronic active AD. Two cases initially appeared as pretibial bursal fluid accumulations, a type of bursitis that is previously undescribed. Onset of bursitis in all cases coincided with flaring of dermatitis. The frequency of these 10 episodes in six patients among an AD population of 792 appears to be greater than the three cases per 1000 in the local Veterans Administration outpatient center. CONCLUSION: The unusual pretibial bursal fluid accumulations in AD, along with multiple recurrences of olecranon bursitis during flares of dermatitis, suggest that the association may not be coincidental.

Adult↗
PubMed1994

Bioactive annonaceous acetogenins from the bark of Xylopia aromatica.

Bioactive Annonaceous acetogenins have been isolated from the EtOH extract of the bark of Xylopia aromatica by bioactivity-directed fractionation using lethality to brine shrimp. These acetogenins include xylopianin [1 , xylopiacin [2], and xylomaticin [3], which are three new mono-tetrahydrofuran ring type acetogenins, in addition to the known compounds, annomontacin, gigantetronenin, gigantetrocin A, and annonacin. Compounds 1 and 2 are unusual in having hydroxylation at C-8; 3 has the same functionalities as annonacin but with 37 carbons instead of 35 carbons. The structures were elucidated by spectral analysis of the parent compounds and/or simple chemical derivatives. These acetogenins showed cytotoxicities, comparable to adriamycin, against three human solid tumor cell lines.

Animals↗
PubMed1994

Function of human renin proximal promoter DNA.

An understanding of the mechanisms involved in the control of the human renin promoter have been hampered and confounded in work to date because of deficiencies in material available and experimental design. The promoter appears to be weak and a good cell model is lacking. Chorio-decidual cultures have been used since these have high renin synthesis, are readily available and grow well in culture. They suffer, however, from phenotypic variability and do not transfect well in transient expression analyses. Recent evidence suggests that 2.6 kb of proximal 5'-flanking DNA is unable to induce native promoter activity under basal conditions. Experiments in which an exogenous enhancer was introduced have raised the possibility that an endogenous enhancer residing outside of the 2.6 kb 5'-flanking region could be required. Cell-type specific factors also appear to be needed. The proximal flanking DNA does, however, appear to be capable of conferring activity on the promoter in chorio-decidual cells under stimulated conditions, suggesting that factors so activated may have considerable importance. Evidence suggests that forskolin-responsive signal transduction pathways may lead cyclic AMP responsive element (CRE) binding protein (CREB) to act on a CRE at -222 in the proximal REN promoter DNA. Activation of the mouse promoter by cAMP appears to involve a different element, however. Furthermore, overall control of renin synthesis is likely to involve post-transcriptional mechanisms as well. Thus, despite being the first cardiovascular gene to be cloned, much more work is required before the control of the human renin gene is fully understood.

Animals↗
PubMed1994

Structure of human neutrophil collagenase reveals large S1' specificity pocket.

The crystal structure of the catalytic domain of human neutrophil collagenase complexed with a peptide transition state analogue has been determined to a resolution of 2.1 A. The structure of the neutrophil enzyme, when compared with the three dimensional structure of the corresponding human fibroblast collagenase, shows differences in the first, S1', of the three enzyme specificity subsites on the carboxy-terminal side of the substrate scissile bond. The S1' pocket in the neutrophil collagenase is significantly larger than the equivalent site in the fibroblast enzyme, suggesting that the former enzyme has a broader range of possible substrates. Such differences also suggest approaches for the design of selective matrix metalloproteinase inhibitors.

Amino Acid Sequence↗
PubMed1994

Common nonarticular syndromes in the elbow, wrist, and hand.

Nonarticular elbow, wrist, and hand discomfort commonly results from periarticular or tendon disorders or nerve entrapment. Physicians with a practical knowledge of upper extremity anatomy and mechanics and an awareness of the typical features of disease are best equipped to treat these often-encountered conditions. Therapy is based on an accurate diagnosis and should be tailored to each disorder.

Arm↗
PubMed1994

The structural basis for the altered substrate specificity of the R292D active site mutant of aspartate aminotransferase from E. coli.

Two refined crystal structures of aspartate aminotransferase from E. coli are reported. The wild type enzyme is in the pyridoxal phosphate (PLP) form and its structure has been determined to 2.4 A resolution, refined to an R-factor of 23.2%. The structure of the Arg292Asp mutant has been determined at 2.8 A resolution, refined to an R-factor of 20.3%. The wild type and mutant crystals are isomorphous and the two structures are very similar, with only minor changes in positions of important active site residues. As residue Arg292 is primarily responsible for the substrate charge specificity in the wild type enzyme, the mutant containing a charge reversal at this position might be expected to catalyze transamination of arginine as efficiently as the wild type enzyme effects transamination of aspartate [Cronin, C.N. and Kirsch, J.F. (1988) Biochemistry, 27, 4572-4579]. This mutant does in fact prefer arginine over aspartate as a substrate, however, the rate of catalysis is much slower than that of the wild type enzyme with its physiological substrate, aspartate. A comparison of these two structures indicates that the poorer catalytic efficiency of R292D, when presented with arginine, is not due to a gross conformational difference, but is rather a consequence of both small side chain and main chain reorientations and the pre-existing active site polar environment, which greatly favors the wild type ion pair interaction.

Arginine↗