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Biomedical subjects

D P Clark

Publications and source records attributed to D P Clark.

At least 73 records · Page 4Linked to original sources
PubMed1989

Escherichia coli derivatives lacking both alcohol dehydrogenase and phosphotransacetylase grow anaerobically by lactate fermentation.

Escherichia coli mutants lacking alcohol dehydrogenase (adh mutants) cannot synthesize the fermentation product ethanol and are unable to grow anaerobically on glucose and other hexoses. Similarly, phosphotransacetylase-negative mutants (pta mutants) neither excrete acetate nor grow anaerobically. However, when a strain carrying an adh deletion was selected for anaerobic growth on glucose, spontaneous pta mutants were isolated. Strains carrying both adh and pta mutations were observed by in vivo nuclear magnetic resonance and shown to produce lactic acid as the major fermentation product. Various combinations of adh pta double mutants regained the ability to grow anaerobically on hexoses, by what amounts to a homolactic fermentation. Unlike wild-type strains, such adh pta double mutants were unable to grow anaerobically on sorbitol or on glucuronic acid. The growth properties of strains carrying various mutations affecting the enzymes of fermentation are discussed in terms of redox balance.

Acetyltransferases↗
PubMed1988

Mutants of Escherichia coli defective in acid fermentation.

Wild type E. coli ferments glucose to a mixture of ethanol and acetic, lactic, formic, and succinic acids. Mutants defective in acid production have now been isolated, including those defective in lactate dehydrogenase (LDH) or with excess alcohol dehydrogenase. These mutations had no phenotype without a pfl mutation. Novel mutants affecting acetate metabolism were isolated by insertion of the fusion vector Mudl. These aceG mutants cannot grow anaerobically on glucose or aerobically on acetate yet lack the pleiotropic growth defects of previously known pta/ack mutants. In some genetic backgrounds acetate negative mutations suppress the growth defects of adh mutations. These results are discussed in terms of redox balance.

Acetates↗
PubMed1988

Benign nasopharyngeal teratomas in the neonate.

Two cases are described of benign teratoma arising in the nasopharynx and presenting with difficulty breathing in the neonatal period. Preservation of the airway is paramount during assessment. Radiology and subsequent examination under anaesthetic, precede removal of the teratoma by snare. This is usually uncomplicated but bleeding has been reported. Complete removal cures the airway problem and follow-up is usually uneventful. A review of the classification and aetiology by these lesions is included.

Airway Obstruction↗
PubMed1988

Subacute cutaneous lupus erythematosus presenting as erythroderma.

We report the first case of subacute cutaneous lupus erythematosus presenting with exfoliative erythroderma. Although our patient had uniquely extensive skin disease, she had the clinical, histologic, serologic, and immunogenetic features of subacute cutaneous lupus erythematosus. Complete remission was obtained with a short course of systemic corticosteroids and long-term hydroxychloroquine therapy. We briefly discuss the usual features of subacute cutaneous lupus erythematosus.

Acute Disease↗
PubMed1988

Mild hemophilia A as a cause of bleeding in dermatologic surgery.

A 63-year-old male had major postoperative bleeding complications following the excision of a basal cell carcinoma. The patient denied a prior history of bleeding complications and had normal coagulation screening studies. After coagulation evaluation, he was found to have mild hemophilia A with 23% of normal Factor VIII C. We discuss an approach to the evaluation of coagulation in patients with perioperative and postoperative bleeding. Also, we outline treatment alternatives for patients with hemophilia A who need cutaneous surgery.

Blood Coagulation↗
PubMed1988

Neoplasms of the conchal bowl: treatment with Mohs micrographic surgery.

Thirty-four patients with tumors in the conchal bowl were treated with Mohs micrographic surgery. Twenty-six patients had basal cell carcinoma and 8 patients had squamous cell carcinoma. Thirty-three of 34 patients achieved a tumor-free margin during initial therapy. All patients remain free of recurrence and metastasis at an average follow-up period of 2.9 years. Thirty-three of 34 patients were allowed to heal by second intention. Only one patient required reconstruction to avoid stenosis of the external auditory canal.

Adult↗
PubMed1988

Accumulation of trehalose by Escherichia coli K-12 at high osmotic pressure depends on the presence of amber suppressors.

When grown at high osmotic pressure, some strains of Escherichia coli K-12 synthesized substantial levels of free sugar and accumulated proline if it was present in the growth medium. The sugar was identified as trehalose by chemical reactivity, gas-liquid chromatography, and nuclear magnetic resonance spectroscopy. Strains of E. coli K-12 could be divided into two major classes with respect to osmoregulation. Those of class A showed a large increase in trehalose levels with increasing medium osmolarity and also accumulated proline from the medium, whereas those in class B showed no accumulation of trehalose or proline. Most class A strains carried suppressor mutations which arose during their derivation from the wild type, whereas the osmodefective strains of class B were suppressor free. When amber suppressor mutations at the supD, supE, or supF loci were introduced into such sup0 osmodefective strains, they became osmotolerant and gained the ability to accumulate trehalose in response to elevated medium osmolarity. It appears that the original K-12 strain of E. coli carries an amber mutation in a gene affecting osmoregulation. Mutants lacking ADP-glucose synthetase (glgC) accumulated trehalose normally, whereas mutants lacking UDP-glucose synthetase (galU) did not make trehalose and grew poorly in medium of high osmolarity. Trehalose synthesis was repressed by exogenous glycine betaine but not by proline.

Betaine↗
PubMed1987

The human multidrug resistance (mdr1) gene. cDNA cloning and transcription initiation.

Multidrug resistance in human KB carcinoma cells selected for resistance to colchicine, vinblastine, or adriamycin results from overexpression, and frequently amplification, of a specific gene (mdr1). Overlapping cDNA clones representing a complete 4.7-kilobase mdr1 transcript have been obtained from multidrug-resistant KB cells. Primer extension and S1 nuclease protection experiments show that two transcripts initiate 136 and 140 bases upstream from the first ATG codon in all human multidrug-resistant cell lines. The mdr1 gene is expressed in human normal kidney cells and HepG2 liver cells as a poly(A)+ RNA which starts from the same sites. Less prominent transcripts were found to initiate 155-180 bases upstream from the first ATG codon in vinblastine- or adriamycin-selected cell lines and 480-630 bases upstream in colchicine-selected cell lines. Southern hybridization analyses with different portions of a full-length cDNA indicate that the human mdr1 gene encompasses at least 70 kilobases of DNA amplified in all highly multidrug-resistant cell lines.

Base Sequence↗
PubMed1987

AI/LEARN: an interactive videodisk system for teaching medical concepts and reasoning.

This paper describes AI/LEARN, an educational videodisk system designed to teach clinical observational skills and reasoning in medicine. The AI/LEARN system uses a learning conditions approach to teaching. To teach visual concepts, we use the principle of exemplar/nonexemplar pairs and immediate feedback. To teach If-Then problem solving we use the format of minicases with delayed feedback. The software to operate the system has been custom developed and is domain independent. The result is a prototype of a new authoring package for videodisk teaching which operates on IBM compatible microcomputers. The medical domain selected for this prototype system was rheumatic diseases; the knowledge used to teach reasoning skills is derived from the knowledge base of an expert system: AI/RHEUM.

Computer Systems↗
PubMed1987

Regulatory mutations that allow the growth of Escherichia coli on butanol as carbon source.

Starting with adhC mutants of Escherichia coli in which alcohol dehydrogenase (ADH) and acetaldehyde CoA dehydrogenase (ACDH) are expressed constitutively at high levels, we selected mutants with still higher levels of both enzymes. Selection for growth on ethanol in the presence of inhibitors of ADH gave several mutants that had from 2- to 10-fold increases in the levels of both enzymes. These mutations were found to map far from the adhC locus at around 90 min. Such adhR mutants were unable to grow on acetate or ethanol in certain media unless supplemented with extra manganese. This growth disability was suppressed by secondary mutations, one of which, aceX, increased sensitivity to several toxic metals and may perhaps derepress Mn transport. When the adhR mutation expressing the highest ADH and ACDH levels was present together with fadR and atoC mutations (allowing efficient catabolism of acetoacetyl-CoA) and with an aceX mutation, the resulting strains became capable of using n-butanol as sole carbon and energy source. The use of butanol by E. coli illustrates the artificial evolution of a new catabolic pathway, in this case by the selection of four successive regulatory mutations (fadR, adhC, atoC, and adhR) together with the poorly defined aceX mutation. Each stage in the acquisition of this novel pathway confers the ability to use a new growth substrate: decanoic acid (fadR), ethanol (adhC), butyric acid (atoC), and butanol (adhR, when present with aceX).

1-Butanol↗
PubMed1987

Genetic engineering of ethanol production in Escherichia coli.

The genes encoding essential enzymes of the fermentative pathway for ethanol production in Zymomonas mobilis, an obligately ethanologenic bacterium, were inserted into Escherichia coli under the control of a common promoter. Alcohol dehydrogenase II and pyruvate decarboxylase from Z. mobilis were expressed at high levels in E. coli, resulting in increased cell growth and the production of ethanol as the principal fermentation product from glucose. These results demonstrate that it is possible to change the fermentation products of an organism, such as E. coli, by the addition of genes encoding appropriate enzymes which form an alternative system for the regeneration of NAD+.

Alcohol Dehydrogenase↗
PubMed1987

Isolation and genetic analysis of mutations allowing the degradation of furans and thiophenes by Escherichia coli.

Successive mutations of Escherichia coli yielded a strain that was able to degrade a variety of heterocyclic oxygen- and sulfur-containing ring compounds. In particular, this strain could use both furan-2-carboxylic acid and thiophene-2-carboxylic acid as sole carbon and energy sources. Nitrogen-containing heterocyclic compounds were not degraded. This mutant was isolated by selecting first for oxidation of furan derivatives and then for thiophene degradation. Genetic analysis revealed that mutations in three novel genes, thdA (12 min), thdC (92 min), and thdD (98 min), were required for thiophene degradation. In addition, constitutively at both of the previously characterized fadR and atoC loci was required for efficient thiophene breakdown. The pathway of furan and thiophene degradation remains obscure, but the inability of our mutants to degrade 5-nitro- or 5-bromo-substituted furan derivatives suggests that hydroxylation at position 5 may be involved. Thiophene derivatives were toxic when they were present at concentrations of 0.1% or greater; however, addition of trace amounts of phenylalanine plus tyrosine greatly reduced this effect.

Escherichia coli↗
PubMed1987

Condyloma acuminatum.

Condylomata acuminata, an HPV infection, is a major health concern. The incidence is rising in the young population, and there is no specific therapy. Aggressive HPV viral types, increasingly found in HPV-related infections, suggest that the affected population will experience a dramatic increase in genitourinary neoplasms during the next decade. Until an HPV-specific vaccine is developed we must treat this difficult condition with nonspecific destructive therapy.

Condylomata Acuminata↗
PubMed1986

Internal duplication and homology with bacterial transport proteins in the mdr1 (P-glycoprotein) gene from multidrug-resistant human cells.

Resistance of tumor cells to multiple cytotoxic drugs is a major impediment to cancer chemotherapy. Multidrug resistance in human cells is determined by the mdr1 gene, encoding a high molecular weight membrane glycoprotein (P-glycoprotein). Complete primary structure of human P-glycoprotein has been determined from the cDNA sequence. The protein, 1280 amino acids long, consists of two homologous parts of approximately equal length. Each half of the protein includes a hydrophobic region with six predicted transmembrane segments and a hydrophilic region. The hydrophilic regions share homology with peripheral membrane components of bacterial active transport systems and include potential nucleotide-binding sites. These results are consistent with a function for P-glycoprotein as an energy-dependent efflux pump responsible for decreased drug accumulation in multidrug-resistant cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1986

The use of suicide substrates to select mutants of Escherichia coli lacking enzymes of alcohol fermentation.

Mutants of Escherichia coli resistant to chloroethanol or to chloroacetaldehyde were selected. Such mutants were found to lack the fermentative coenzyme A (CoA) linked acetaldehyde dehydrogenase activity. Most also lacked the associated fermentative enzyme alcohol dehydrogenase. Both types of mutants, those lacking acetaldehyde dehydrogenase alone or lacking both enzymes, mapped close to the regulatory adhC gene at 27 min on the E. coli genetic map. The previously described acd mutants which lack acetaldehyde dehydrogenase and which map at 63 min were shown to be pleiotropic, affecting respiration and growth on a variety of substrates. It therefore seems likely that the structural genes for both the acetaldehyde and alcohol dehydrogenases lie in the adhCE operon. This interpretation was confirmed by the isolation of temperature sensitive chloracetaldehyde-resistant mutants, some of which produced thermolabile acetaldehyde dehydrogenase and alcohol dehydrogenase and were also found to map at the adh locus. Reversion analysis indicated that mutants lacking one or both enzymes carried single mutations. The gene order in the adh region was determined by three point crosses to be trp-zch::Tn10-adh-galU-bglY-tyrT-chlC.

Acetaldehyde↗