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Biomedical subjects

H C Lin

Publications and source records attributed to H C Lin.

At least 397 records · Page 22Linked to original sources
PubMed1985

Cloning of the pectate lyase genes from Erwinia carotovora and their expression in Escherichia coli.

A hybrid cosmid coding for pectate lyase (PL) activity was identified from an Erwinia carotovora genomic library by an immunological screening method. A 7-kb DNA fragment was identified which codes for three proteins identical in size to proteins with PL activity purified from E. carotovora culture supernatants. The three proteins had apparent Mrs of 41, 44 and 44 X 10(3) as estimated by SDS-PAGE. None of the PLs were exported from Escherichia coli strain HB101 but all were found in the periplasmic space. Plant tissue was macerated by the PLs made in E. coli.

Bacterial Proteins↗
PubMed1985

The araBAD operon of Salmonella typhimurium LT2. I. Nucleotide sequence of araB and primary structure of its product, ribulokinase.

Hybrid plasmids containing the araBAD operon of Salmonella typhimurium LT2 were characterized by Southern blot and genetic analyses. The nucleotide sequence of araB was determined. The araB gene product, ribulokinase (EC 2.7.1.16), was purified and the results of amino acid composition analysis and partial amino acid sequence are in agreement with predictions from the DNA sequence. Ribulokinase is 569 amino acid residues long and has a calculated Mr of 61 793. Ribulokinase shares significant homology with xylulose kinase from Escherichia coli. Codon usage in the araB gene does not favor those codons which have intermediate codon-anticodon binding energy.

Amino Acid Sequence↗
PubMed1985

The araBAD operon of Salmonella typhimurium LT2. II. Nucleotide sequence of araA and primary structure of its product, L-arabinose isomerase.

The nucleotide sequence of gene araA of Salmonella typhimurium LT2 has been determined. The gene encodes an L-arabinose isomerase (EC 5.3.1.4) of 500 amino acid residues with a calculated Mr of 55814. The ATG start codon of araA is 10 bp distal to the TAA termination codon of araB. A presumed ribosome-binding site (RBS) "TAAGGA" 7 bp from the ATG codon overlaps the stop codon of araB. L-Arabinose isomerase was purified and the amino acid composition is in agreement with that predicted from the DNA sequence. The NH2-terminus of the protein is modified as the sequence cannot be analyzed by the automated Edman degradation. Amino acid composition analyses of both NH2-terminal and C-terminal cyanogen bromide (CNBr) cleaved peptides and partial amino acid sequence of the C-terminal peptide are consistent with the deduced amino acid sequence.

Aldose-Ketose Isomerases↗
PubMed1985

The araBAD operon of Salmonella typhimurium LT2. III. Nucleotide sequence of araD and its flanking regions, and primary structure of its product, L-ribulose-5-phosphate 4-epimerase.

The araD gene of Salmonella typhimurium LT2 consists of 744 nucleotides and has an ORF coding for a protein of 248 amino acid residues with a calculated Mr of 27059. The product of araD, L-ribulose-5-phosphate 4-epimerase, was purified and the amino terminal sequence was determined. It is identical to that predicted by the ORF. A 143-bp intercistronic region was found between the araA and araD genes which can form stem-loop structures with calculated free energies of up to -76.7 kcal/mol. Three sets of sequences within this 143-bp region are comparable to a consensus sequence deduced from several known intercistronic regions. Approximately equimolar amounts of the araBAD operon products were present in L-arabinose-induced cells. Sequences similar to both rho-independent and rho-dependent transcription terminators are present after the araD gene.

Amino Acid Sequence↗
PubMed1985

araB Gene and nucleotide sequence of the araC gene of Erwinia carotovora.

The araB and araC genes of Erwinia carotovora were expressed in Escherichia coli and Salmonella typhimurium. The araB and araC genes in E. coli, E. carotovora, and S. typhimurium were transcribed in divergent directions. In E. carotovora, the araB and araC genes were separated by 3.5 kilobase pairs, whereas in E. coli and S. typhimurium they were separated by 147 base pairs. The nucleotide sequence of the E. carotovora araC gene was determined. The predicted sequence of AraC protein of E. carotovora was 18 and 29 amino acids longer than that of AraC protein of E. coli and S. typhimurium, respectively. The DNA sequence of the araC gene of E. carotovora was 58% homologous to that of E. coli and 59% homologous to that of S. typhimurium, with respect to the common region they share. The predicted amino acid sequence of AraC protein was 57% homologous to that of E. coli and 58% homologous to that of S. typhimurium. The 5' noncoding regions of the araB and araC genes of E. carotovora had little homology to either of the other two species.

Amino Acid Sequence↗
PubMed1985

Evidence that polygalacturonase is a virulence determinant in Erwinia carotovora.

Polygalacturonase (PG) was purified from Erwinia carotovora EC. A hybrid cosmid, pSH711, that encodes PG activity but not pectate lyase activity was identified from an E. carotovora genomic library by an immunological screening method. A cell extract of Escherichia coli cells containing pSH711 was able to produce plant tissue maceration when spotted on carrot, potato, or turnip slices. In addition, the E. coli strain containing this plasmid was able to macerate carrot, potato, and turnip slices. Our results suggest that PG plays an important role in soft-rot disease.

Cloning, Molecular↗
PubMed1985

[Cytogenic chorionic nodule of the uterus].

The authors report five observations of endometrial stromal nodules. These nodules are composed of cells identical to those of the endometrial stroma. They constitute the benign form of endometrial stromal tumors. From the macroscopic point of view, they present as nodular formations, most often single, well defined, non-fasciculated, whitish or yellowish sometimes cystisized. From the microscopic point of view, these nodules contain areas of plexiform or glandular arrangement with, occasionally, pseudo-rosettes. Small collagenous zones can often be observed. E.S.N. should be distinguished on the one hand from endolymphatic stromal myosis, and on the other hand from sarcoma of the endometrial stroma. Histogenesis of the lesion is also discussed.

Adult↗
PubMed1984

High tension electrical burns of upper arms treated by segmental excision of necrosed humerus. An introduction of a new surgical method.

This paper describes treating high-tension electrical burns of the upper arms by segmental excision of the necrosed humerus. This is a new surgical method of treating local electrical burns. The authors use modification of traditional surgical method, shorten the course of treatment, and preserve the injured limb. However, this surgical method should not be used to treat all high-tension electrical burns of the upper arm, and should be used only under certain conditions. Therefore, it is important to grasp the operative indications.

Adult↗
PubMed1984

Structure and composition of microcalcifications in benign and malignant lesions of the breast: study by light microscopy, transmission and scanning electron microscopy, microprobe analysis, and X-ray diffraction.

Microcalcifications previously located by radiography were extracted from 25 fresh specimens obtained from patients who had undergone tumorectomy or systematized mammary exeresis. Two principal types of microcalcifications were distinguished: Type I microcalcifications were amber in color and generally crystalline on scanning electron microscopy, with only one calcium peak on microprobe analysis; x-ray diffraction revealed that weddellite was involved. Type II microcalcifications were whitish, nonbirefringent under polarized light, and generally ovoid or fusiform, with two peaks, one calcium and the other phosphorus, on microprobe analysis; these microcalcifications were composed of calcium phosphate, the most characteristic form of which is hydroxyapatite, in the form of needles arranged in rosettes on transmission electron microscopy. Type I microcalcifications were observed in four of eight benign breast lesions, in two of three in situ lobular carcinomas, and in no intraductal adenocarcinomas or infiltrating carcinomas. Type II microcalcifications were present in all infiltrating carcinomas and intraductal adenocarcinomas; they were also found in benign lesions (four of eight) and even associated with type I microcalcifications in one in situ lobular carcinoma. There are, therefore, no "benign" or "malignant" microcalcifications; however, the presence of weddellite is a strong indication that a lesion is benign or, at most, an in situ lobular carcinoma.

Adenocarcinoma↗
PubMed1984

[Basement membranes of epithelial tumors of the ovary. Histochemical and immunohistochemical study using antibodies to collagen IV, III, I and to laminin].

Thirteen ovarian tumours were the subject of a histochemical and immunohistochemical study using antibodies to collagen IV, III, I, and to laminin. Our study shows that it is not possible to assess the integrity of the basement membrane using simple histochemical methods (P.A.S., Gordon Sweets staining). In contrast, in benign epithelial tumours, a continuous basement membrane may be visualized beneath the epithelium of the cysts using antibodies to collagen IV and to laminin, collagen IV and laminin being two of the constituents of basement membranes. In malignant epithelial tumours, the immunoreactive material of collagen IV type or of laminin type, is arranged in a distinctly discontinuous manner, and is of unequal thickness around the edge of the cysts or of the neoplastic clusters. In three cases of borderline epithelial tumours, the discontinuity of the immunoreactive material (collagen IV or laminin) lying beneath the epithelium of the cysts, is not so pronounced. In comparison with studies carried out on the cervix uteri, this latter type of tumor, because of the constitution of its basement membranes, would appear to occur at a particular moment in their evolution, i.e. when they pass from the intra-epithelial stage and become infiltrative.

Antibodies, Neoplasm↗
PubMed1982

The nucleotide sequence of the araC regulatory gene in Salmonella typhimurium LT2.

The nucleotide sequence of the araC regulatory gene of Salmonella typhimurium LT2 has been determined. This sequence and the predicted araC translational product are compared to their counterparts in Escherichia coli. The two genes code for similar products although the S. typhimurium protein is eleven amino acids shorter than the E. coli protein. The predicted amino acid sequences are 92% conserved and the DNA sequences are 82% conserved for the common regions of the two genes.

Amino Acid Sequence↗
PubMed1980

Surface activities of tertiary amine local anesthetics at air/water interface in the presence and absence of phospholipid monolayers.

Adsorption of procaine and tetracaine to the dipalmitoyl phosphatidylcholine monolayers at the air/water interface is analyzed in terms of two types of interaction: (1) between the phospholipid molecules and the ligand molecules, and (2) among the ligand molecules themselves. The presence of the phospholipid monolayer increases the surface concentration of the anesthetics. The interaction energy, omega AB, between the phospholipid molecules and the anesthetic molecules at the interface accounts for this excess adsorption. The values were --2.95 kT for procaine and --2.99 kT for tetracaine where k is the Boltzmann constant and T = 298 K. The adsorption of the local anesthetics to the interface was cooperative. The interaction energy, omega AA, between the anesthetics molecules on the surface determines the cooperativity. The values were --0.056 kT for procaine and --0.397 kT for tetracaine, where T = 298 K. This parameter determines the slope of the curve plotted relating the surface concentration (gamma) and the logarithm of the bulk concentration (log C). When (omega AA/kT) greater than or equal to 1, the adsorption follows the phase-transition. A parameter KA, which is related to the difference of the free energy of anesthetics between the surface and the bulk molecules, locates the take-off point of the adsorption curve at the log C axis. The values were 2.15 x 10(3) for procaine and 7.00 x 10(3) for tetracaine. In spite of the general assumption that the difference in the clinical potency among local anesthetics are attributable to their lipid solubility, the present results showed that the phospholipid-anesthetic interaction energies for procaine and tetracaine were similar. The larger surface concentration of tetracaine than procaine at the same bulk concentration was due to the combined effect of KA and omega AA. KA represents the tendency of the anesthetic molecules to escape from the hydrogen-bonded water phase, and omega AA determines the cooperativity factor causing these molecules to aggregate at the interface. It was also observed that the charged forms of the anesthetics have non-zero surface activities.

Adsorption↗
PubMed1978

Variation of isomer distribution in electrophilic nitration of toluene, anisole, and o-xylene: Independence of high regioselectivity from reactivity of reagent.

The nitration of toluene and anisole was studied with nitrating systems of varying reactivity. High regioselectivity of ortho-para over meta substitution was maintained in all nitrations, regardless of the reactivity of the nitrating system. At the same time, the amount of meta substitution stayed low (3% or less), even when the fast reactions may have reached the encounter-controlled limit. Because the nitration of o-xylene, in which both ring positions are activated by the effect of a methyl group, also does not show any diminishing of regioselectivity, the possibility of a dual mechanistic pathway, in which the activated position would react by a fast, encounter-controlled path, whereas the nonactivated meta position by a slower sigma-type path, can be ruled out. The data unambiguously prove that the high regioselectivity of electrophilic aromatic nitration is independent of the reactivity of the reagent, because no significant increase of meta substitution of toluene or anisole was observed, regardless of the activity of the nitrating system. No selectivity-reactivity relationship is thus evident and the ortho-para directing effect of primary substituents over meta substitution is always maintained. The variation in the amount of the meta isomer, up to the observed limit of about 3% in the case of toluene and <2% for anisole, is probably significant but, at the present time, cannot be quantitatively evaluated with the +/-0.5% overall reproducible accuracy of the nitrations. Steric factors, such as increasing bulkiness of the nitrating agent, also can affect the ortho-para isomer ratios but are not considered to be the only reason for the observed variations, which reflect the specific nitrating systems, affecting the nature and position of the transition state of highest energy on the reaction pathway.

Journal Article↗
PubMed1978

Electrophilic and free radical nitration of benzene and toluene with various nitrating agents.

Electrophilic nitration of toluene and benzene was studied under various conditions with several nitrating systems. It was found that high orthopara regioselectivity is prevalent in all reactions and is independent of the reactivity of the nitrating agent. The methyl group of toluene is predominantly ortho-para directing under all reaction conditions. Steric factors are considered to be important but not the sole reason for the variation in the ortho/para ratio. The results reinforce our earlier views that, in electrophilic aromatic nitrations with reactive nitrating agents, substrate and positional selectivities are determined in two separate steps. The first step involves a pi-aromatic-NO(2) (+) ion complex or encounter pair, whereas the subsequent step is of arenium ion nature (separate for the ortho, meta, and para positions). The former determines substrate selectivity, whereas the latter determines regioselectivity. Thermal free radical nitration of benzene and toluene with tetranitromethane in sharp contrast gave nearly statistical product distributions.

Journal Article↗