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Biomedical subjects

L Chao

Publications and source records attributed to L Chao.

At least 217 records · Page 12Linked to original sources
PubMed1985

Evolution of transposable elements: an IS10 insertion increases fitness in Escherichia coli.

Strains of Escherichia coli carrying Tn10, a transposon consisting of two IS10 insertion sequences flanking a segment encoding for a tetracycline-resistance determinant, gain a competitive advantage in chemostat cultures. All Tn10-bearing strains that increase in frequency during competition have a new IS10 insertion that is found in the same location in the genome of those strains. We mapped, by a gradient of transmission, the position of the new IS10 insertion. We examined 11 isolates whose IS10 insertion was deleted by recombinational crossing-over, and in all cases the competitive fitness of the isolates was decreased. These results show that the IS10-generated insertion increases fitness in chemostat cultures. We named the insertion fit::IS10 and suggest that transposable elements may speed the rate of evolution by promoting nonhomologous recombination between preexisting variations within a genome and thereby generating adaptive variation.

Biological Evolution↗
PubMed1985

The effects of wall populations on coexistence of bacteria in the liquid phase of chemostat cultures.

We have examined the effects of wall populations on coexistence between strains of Escherichia coli in the liquid phase of mixed (two-strain) chemostats. The wall populations of the two competing strains became established soon after the start of the cultures and, although the relative abundance of the strains in the liquid phase could change over time by several orders of magnitude, the composition of an established wall population did not change markedly. The bacterial strains examined could not displace an established wall population of a competing strain. The presence of a permanent wall population allowed a strain that was less fit in the liquid phase to coexist with a superior strain. The resulting coexistence did not require that the inferior strain attached to the vessel wall better than the superior strain. We believe that the coexistence developed because the inferior strain survived and reproduced on the vessel wall. The progeny from that wall population then provided replacements for the bacteria that the inferior strain lost through a selective disadvantage in the liquid phase of the culture. By replacing the chemostat vessel, hence eliminating the wall populations, we could distinguish between cases where the coexistence depended on the presence of a wall population and where it resulted from some alternative mechanism.

Bacteriological Techniques↗
PubMed1984

Isolation of tissue kallikrein in rat spleen by monoclonal antibody-affinity chromatography.

Rat spleen kallikrein was identified and purified by DEAE-cellulose and monoclonal antibody-affinity chromatography. The purified enzyme has Tos-Arg-OMe esterase activity and kinin-releasing activity from a purified low-molecular-weight kininogen substrate. In the direct radioimmunoassay for tissue kallikrein, the splenic enzyme displays parallelism with standard curves of rat urinary kallikrein. The pH profiles of the Tos-Arg-OMe esterase activities of spleen and urinary kallikrein were identical with optima at 9.0. Rat spleen kallikrein was inhibited strongly by aprotinin and affinity-purified kallikrein antibody and weakly by soybean trypsin inhibitor. The IC50 values were similar to those observed against rat urinary kallikrein. Neither the urinary nor the splenic enzyme was inhibited by lima bean trypsin inhibitor or preimmune serum immunoglobulins. Spleen kallikrein was labeled with [14C]diisopropylphosphorofluoridate and visualized by fluorography on a sodium dodecyl sulfate-polyacrylamide gel. The electrophoretic mobility of the splenic enzyme was indistinguishable from that of urinary kallikrein A with an estimated Mr of approx. 38 000. With Western blot analyses using a rabbit anti-kallikrein antibody followed by 125I-labeled protein A binding, the spleen and urinary kallikreins were again visualized at identical positions by autoradiography. The data show that there is a rat splenic tissue kallikrein which is indistinguishable from a renal kallikrein with respect to physicochemical properties, immunological character and susceptibility to inhibitors.

Animals↗
PubMed1984

Identification of a kallikrein-like latent serine protease in human erythrocyte membranes.

We have discovered and characterized a kallikrein-like latent serine protease in intact human erythrocytes and ghosts. The enzyme is activatable by trypsin. The solubilized enzyme has esterolytic activity with a pH optimum of 9; but the membrane-associated activity increases almost linearly up to pH 10. The activated enzyme releases kinin from bovine low molecular weight kininogen. Enzyme activity is inhibited by TosLysCH2Cl , phenylmethylsulfonyl fluoride, aprotinin and amiloride, and weakly by soybean or lima bean trypsin inhibitor. It is inhibited by Co2+, Zn2+ and Mn2+ but is stimulated by Fe2+, deoxycholate and phospholipase A2. An erythrocyte membrane protein (Mr = 88,000) with an active site serine residue was identified with [14C]-diisopropylphosphorofluoridate labeling. Consistent with the finding of tryptic activation of the latent erythrocyte serine protease, trypsin treatment reduced the density of labeling of this protein and revealed a lower molecular weight form (Mr = 64,000). Possible relationships between the activity of this newly identified serine protease and events such as erythrocyte membrane ion fluxes might be of interest.

Binding Sites↗
PubMed1984

Free transplantation of sub-axillary lateral thoraco-dorsal flap in burn surgery.

Free transplantation of subaxillary lateral thoracodorsal flap is recommended. The thoraco-dorsal artery and its accompanying veins may nourish and drain a large musculo-cutaneous flap. The calibres of both the artery and the veins are big enough to be anastomosed to the recipient vessels using the naked eye. The donor area can be closed by first intention suture without interfering with the functional recovery of the donor area. Both the functional and cosmetic results after free transplantations of this flap are good. In acute electrical or other deep burns, this flap can be used to prevent infection, to protect the deep vital structures, and to lessen the amputation rate. A better condition is created for functional recovery and facilitating reconstructive surgery. The muscular branch of the thoraco-dorsal artery was always present in our 50 patients whereas only 20 cases (40 per cent) had an independent cutaneous branch which nourishes the flap. We stress the point of preserving and using the muscular branch as the main blood vessel to be anastomosed for this free flap.

Axilla↗
PubMed1983

Identification of tissue kallikrein in brain and in the cell-free translation product encoded by brain mRNA.

A monoclonal antibody against purified rat urinary kallikrein was coupled to agarose and used to isolate kallikrein from rat brain. The purified enzyme has N alpha-tosyl-L-arginine methyl esterase activity with a pH optimum at 9.0, kinin-releasing activity from a purified low molecular weight kininogen, and a parallelism with standard curves of rat urinary kallikrein in a direct radioimmunoassay. Brain kallikrein is inhibited by a series of tissue kallikrein inhibitors with IC50 values similar to those for urinary kallikrein. The purified brain enzyme was labeled with [14C]diisopropylphosphorofluoridate and visualized by fluorography on a sodium dodecyl sulfate-polyacrylamide gel. Electrophoretic mobility of the enzyme was closely similar to that of urinary kallikrein with estimated Mr of approximately 38,000. With Western blot analyses using a rabbit anti-kallikrein antibody, both brain and urinary kallikrein were visualized at identical positions by immunoperoxidase staining and by autoradiography with 125I-protein A binding. Brain mRNA was used to direct cell-free protein synthesis in wheat germ and rabbit reticulocyte lysate systems. [35S]Methionine-labeled kallikrein was identified by fluorography of sodium dodecyl sulfate-polyacrylamide gels after the translation products were subject to immunoprecipitation with affinity-purified kallikrein antibody. Collectively, the data show that tissue kallikrein exists in brain and can be synthesized by brain mRNA.

Animals↗
PubMed1983

New concepts in medical bacteriology.

Traditional tests employed in a clinical microbiology laboratory for speciation of bacteria rely upon the presence of one or more gene products (biochemical profile) from a population of bacterial cells. These traits have been stable over a relatively long period of time, and the techniques have served us well. Current technology allows for modification and potential improvement of this system. By chemically separating DNA strands and employing recombinant DNA techniques, direct identification of bacteria becomes possible. These methods can be adapted directly to the clinical setting. In addition, specific gene products yield clinical disease; monoclonal antibodies directed against these products may speciate a bacterium indirectly through a unique gene product. Specific gene products also provide markers for epidemiologic investigation. All these technologies should find frequent clinical application in the next several years. The discoveries a century ago that germs cause infection and that different germs cause different infections prompted the development of a system of taxonomy for pathogenic microbes. It then became apparent that the identity of the germ infecting a patient could tell us more about his or her diagnosis and prognosis than could all of the clinical skills accumulated up to that time.

Anti-Bacterial Agents↗
PubMed1982

Enhanced resistance to nitrosoguanidine killing and mutagenesis in a DNA gyrase mutant of Escherichia coli.

The role of DNA gyrase in handling DNA damages induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was examined with two Escherichia coli strains, KL161 and KL166. The two strains are isogenic except that KL166 harbors a mutation at the nalA (gyrA) locus which specifies one of the two subunits of DNA gyrase. We treated the two strains with several different types of mutagenic agents and found the nalA strain to be highly resistant to MNNG-induced killing and mutagenic effects as compared with the parental strain. The MNNG resistance was specific, since the two strains were about equally sensitive to methyl methane sulfonate, ethyl methane sulfonate, and UV and gamma radiations. We pulse-labeled the two strains with [(3)H]uridine and (14)C-amino acids after MNNG treatment to analyze RNA and protein synthetic rates. The pulse-labeled proteins were also separated on polyacrylamide gels. The results show that pulse-labeled RNA and proteins persisted in the nalA strain but declined rapidly in the parental strain after MNNG treatment. We compared membrane-free nucleoid preparations from the two strains by sucrose density gradient centrifugation and found a difference in nucleoid organization between the two strains. The nucleoid of the nalA strain, unlike that of the parental strain, may have a highly ordered structure, as indicated by its resistance to ethidium bromide-induced relaxation. The ability of the two strains to express an adaptive response to MNNG was determined. We found that the resistance to MNNG killing and mutagenesis by the nalA strain cannot be further increased by adaptive treatment. These results suggest that an alteration in DNA gyrase may have profound effects on E. coli chromosome organization and base methylation by MNNG.

Bacterial Proteins↗
PubMed1981

Altered stability and integration frequency of a F' factor in RNA polymerase mutants of Escherichia coli.

A number of spontaneous rifampicin-resistant (Rifr) mutants were isolated from a strain of E. coli having a deletion in the lac proA proB region of the chromosome. The stability of a F'lac proA proB episome in these mutants was determined by their sensitivity to acridine orange curing and the frequency of spontaneous loss of episomes. The Rifr mutants can be divided into three classes based on their ability to maintain the F'lac pro episome. Class I mutants (25% of the total Rifr mutants) showed high degree of spontaneous episome loss and high sensitivity to acridine orange curing. Class II mutants (55% of the total Rifr mutants), like the parent strains, showed intermediate sensitivity to acridine orange curing. Class III mutants (21% of the total Rifr mutants) showed high resistance to acridine orange curing and low frequency of spontaneous episome loss. Three-fourths of the Class II mutants were found to be Hfr as shown by their lack of the F'lac pro DNA band on agarose gel together with their ability to mobilize chromosomal markers in mating. Representative Rifr mutants from each class were selected and the Rifr mutants from each class were selected and the Rifr mutations were mapped within the proB gene for the beta beta' operon by P1 transduction. These results indicate that RNA polymerase, or the beta subunit of RNA polymerase, plays an important role in maintaining the F' lac pro episome and in the integration of the F' lac pro episome where no extensive sequence homology is involved.

DNA-Directed RNA Polymerases↗
PubMed1981

Structured habitats and the evolution of anticompetitor toxins in bacteria.

We demonstrate that in liquid cultures, defined in this study as a mass habitat, the outcome of competition between Escherichia coli that produce an antibacterial toxin (colicin) and sensitive E. coli is frequency dependent; the colicinogenic bacteria are at an advantage only when fairly common (frequencies in excess of 2 X 10(-2)). However, we also show that in a soft agar matrix, a structured habitat, the colicinogenic bacteria have an advantage even when initially rare (frequencies as low as 10(-6)). These contrasting outcomes are attributed to the colicinogenic bacteria's lower intrinsic growth rate relative to the sensitive bacteria and the different manner in which bacteria and resources are partitioned in the two types of habitats. Bacteria in a liquid culture exist as randomly distributed individuals and the killing of sensitive bacteria by the colicin augments the amount of resource available to the colicinogenic bacteria to an extent identical to that experienced by the surviving sensitive bacteria. On the other hand, the bacteria in a soft agar matrix exist as single-clone colonies. As the colicinogenic colonies release colicin, they kill neighboring sensitive bacteria and form an inhibition zone around themselves. By this action, they increase the concentration of resources around themselves and overcome their growth rate disadvantage. We suggest that structured habitats are more favorable for the evolution of colicinogenic bacteria.

Biological Evolution↗
PubMed1981

In vitro transformation of Syrian hamster epidermal cells by N-methyl-N'-nitro-N-nitrosoguanidine.

The selection of Syrian hamster epidermal cells which do not terminally differentiate has provided a quantitative focus assay for in vitro chemical transformation. One-day-old Syrian hamster epidermal cells plated at 5 x 10(6)/100-mm dish were treated for 5 hr with various concentrations of N-methyl-N'-nitro-N-nitrosoguanidine. After 4 weeks, the normal epidermal cells began to terminally differentiate to keratinized squamous cells and died, but transformed epidermal colonies grew to higher cells densities and appeared as darker areas against a lightly stained normal cell background. Transformed epidermal foci were isolated and subcultured for at least 15 passages, whereas normal epidermal cells could not be subcultured under the same conditions. The transformed cells assumed the typical cobblestone-like morphology of epithelial cells, retained desmosomes and tonofilaments, and were able to use citrulline in place of arginine. Argininosuccinate synthetase (EC 6.3.4.5) activity was significantly higher in the epidermal cells than in fibroblasts. The injection of 5 x 10(6) cells of two transformed epidermal cell lines into athymic nude mice resulted in the formation of tumors which were identified as keratinizing squamous carcinomas.

Animals↗
PubMed1980

Urinary excretion of 3-methylhistidine as an index of muscle protein catabolism in postoperative trauma: the effect of parenteral nutrition.

The effect of different intravenous nutritional regimens on nitrogen balance and 3-methylhistidine (3-MeHIS) excretion were studied during a 6-day period following major elective surgery in 28 patients. All patients were kept on a synthetic diet 4 days prior to surgery and were given 0.1 g amino acid N and 120 kJ/kg . day. Postoperatively, all patients received parenteral nutrition with approximately 170 kJ/kg . day. Postoperatively, all patients received parenteral nutrition with approximately 170 kJ/kg . day. Three groups of patients were given varying amounts and proportions of amino acids while in one group no amino acids were administered. Preoperatively, urinary 3-MeHIS excretion (determined by a newly developed automatic analyzer) was 240.3 mumole/day +/- 9.2, nitrogen balance was -1.8 g N +/- 0.19. Postoperatively, nitrogen balance was less negative when amino acids were given. The degree of improvement depended on the amount, but not on the composition of nitrogen administered. In all four groups, 3-MeHIS outputs were elevated when compared with preoperative excretion. The 3-MeHIS excretion (mumole/day) was increased more in patients on high amino acid supply than in patients with low or no nitrogen supply. In each of the groups the 3-MeHIS excretion was negatively correlated to the nitrogen balance. Regression analyses suggest that postoperative muscle protein breakdown occurs in relation to the body protein loss. Amino acid administration seems not to decrease muscle protein breakdown, but rather, appears to stimulate protein synthesis, resulting in less net protein loss. The mean rate of muscle protein breakdown in the postoperative state was estimated to be 80 g/day, assuming 4.2 mumole 3-MeHIS per g mixed human muscle protein. This exceeded the mean preoperative breakdown by about 23 g muscle protein per day. This increase might be due to the metabolic response to the trauma and also in part to tissue damage by the surgical procedure.

Aged↗
PubMed1980

Biochemical changes associated with severe trauma.

The effects of different intravenous nutritional regimens on a number of biochemical indices of nutritional status were studied during the 8-day period following severe trauma. The inclusion of large amounts of amino acids (high nitrogen (N) was shown to greatly improve N balance over an isocaloric regimen containing no amino acids (O g N). The concentration of serum albumin, transferrin, prealbumin, and retinol-binding protein all fell during the study period in both patient groups, whereas the serum concentrations of acute phase reactants and of ribonuclease increased in the two groups. The sum of plasma levels of branched-chain amino acids and the essential amino acids was increased to a greater extent in the high N group. These amino acid totals and the ratio of glycine/valine showed a significant correlation with N balance in this group. Despite the marked difference in N balance, 3-methylhistidine excretion was increased but equal in the two nutritional groups, suggesting an increased rate of muscle protein breakdown in both groups, which appears not to be influenced by amino acid nutrition. It is concluded that N balance can be significantly improved in the immediate posttrauma period by provision of amino acids together with energy substrates. None of the biochemical variables measured, with the exception of plasma levels of essential amino acids, reflected these marked differences in N balance.

Adult↗