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Biomedical subjects

L Chao

Publications and source records attributed to L Chao.

229 records · Page 13Linked to original sources
PubMed1977

Nalidixic acid-induced protein alterations in Escherichia coli.

The effect of nalidixic acid on pulse-labeled protein patterns was analyzed by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis. The drug was found to alter protein patterns in a drug-sensitive strain but not in the isogenic drug-resistant strain of Escherichia coli. The drug-induced alteration of protein patterns was demonstrated by the appearance of some and the disappearance of other pulse-labeled peptides elicited by the drug.

Bacterial Proteins↗
PubMed1972

Ribonucleotides covalently linked to deoxyribonucleic acid in T4 bacteriophage.

Bacteriophage T4 was grown in the presence of labeled uridine. The deoxyribonucleic acid (DNA) of the phage was shown to contain covalently attached ribonucleotides. The label appears not to be internal in the DNA strands. Presumably, it is at the ends of the DNA strands and this may be related to DNA initiation.

Carbon Isotopes↗
PubMed1971

Purification and properties of glycogen isolated from a blue-green alga, Nostoc muscorum.

Alpha granules were isolated from a blue-green alga, Nostoc muscorum, in large quantities and high purity by sucrose density gradient centrifugation. Sodium deoxycholate was used to eliminate membrane contamination. Isolated alpha granules from this species have average dimension of 31 nm in width and 65 nm in length. Each alpha granule consists of two equal parts. Attempts to dissociate the intact granule under mild conditions into relatively large subunits did not succeed. Analytical centrifugation of the alpha granules yields a sedimentation coefficient of 265S (S(20, w)). Chemical analysis reveals that alpha granules contain highly branched polyglucosyl units with short external chain lengths.

Amylases↗
PubMedDate not supplied

The purification of human urinary kallikrein with ion-exchange radial flow membrane chromatography.

A method was developed for the purification of kallikrein from human urine. The procedure consisted of three steps: ultradialysis, diethyl-(2-hydroxypropyl) aminoethyl (QAE) ion exchange radial flow membrane chromatography and affinity chromatography on aprotinin agarose. It is simple and suitable for large-scale purification. The purified product was checked by SDS-PAGE and matrix-assisted laser desorption:ionization mass spectrometery (MALDI). A single band with apparent molecular weight (MW) 42,000 in SDS-PAGE and a single monomer peak with MW33,000 in MALDI were observed, respectively. The biological activity tested by ELISA showed positive immunological identity of the purified product compared with human urinary kallikrein standard.

Amino Acid Sequence↗
PubMedDate not supplied

Absorption of di- and tripeptides by the intestine of the guinea-pig.

This paper describes a method of quantifying the amount of smaller peptides in physiological fluids and reports the preliminary results of studying the mesenteric blood of adult guinea-pigs during absorption of a partial hydrolysate of casein. Because of the different roles suggested for plasma and erythrocytes in the inter-organ transport of amino acids, both plasma and whole blood have been studied. Whole blood and plasma samples were deproteinized with sulphosalicylic acid, and amino acids and small peptides separated from residual small amounts of protein on a Sephadex G-25 column. Ion exchange chromatography was then performed before and after acid hydrolysis. The concentration of small peptides in blood seems to be much lower than was previously believed. The adult guinea-pig did not absorb small peptides across the intestine into mesenteric whole blood or plasma in our experiments. However, casein hydrolysates are not necessarily representative of all protein hydrolysates, and further studies are required using different proteins and varying degrees of hydrolysis. The possibility of peptide transfer during development, and in conditions involving mucosal damage, should also be investigated. The present investigation confirms the assumption that predominantly plasma, and not red blood corpuscles, carries amino acids from the gut to the liver. It is worth noting, however, that taurine, aspartic acid, glutamic acid, citrulline and arginine were found in higher concentrations in whole mesenteric blood than in plasma.

Amino Acids↗
PubMedDate not supplied

Transposable elements as mutator genes in evolution.

Strains of the bacterium Escherichia coli harbouring genes that increase mutation rates are known to have an evolutionary advantage in chemostat competition over otherwise isogeneic strains with lower mutation rates. This advantage is frequency-dependent, the mutator strain being favoured only above a starting ratio of approximately 5 x 10(-5), and it results from the fact that the necessary beneficial mutations cannot be generated in a mutator population below a certain size. Here we consider the possibility that the mutagenic properties of transposable elements confer an advantage in the same manner as mutator genes. A previous report has shown that the transposon Tn5 increases the fitness of E. coli in chemostats, although the reason for this effect has not been established. Our results show that the transposon Tn10 also confers an advantage in chemostats. In addition, we find that (1) this advantage, like that associated with mutator genes, is frequency-dependent, (2) whenever the Tn10 strains win, a segment of Tn10, probably its IS10 sequences, has undergone transposition to a new site, (3) the new insertions converge into a site contained within a 3.2 kilobase (kb) PvuII fragment of the genome, and (4) no transpositions are detected when the Tn10 population loses. We conclude that Tn10 confers an advantage by increasing the mutation rate of the host bacterium.

Biological Evolution↗
PubMedDate not supplied

Laboratory surveillance of synergy between and resistance to trimethoprim and sulfonamides.

Results of susceptibility tests of Enterobacteriaceae isolated at 14 different centers demonstrate synergy between trimethoprim (TMP) and sulfamethoxazole (SMZ) against sulfonamide-susceptible isolates, which account for between less than 50% and greater than 75% of the isolates at different centers. Only 1%-4% of the isolates of Escherichia coli or Proteus mirabilis from the five centers in the United States were found to be resistant when tested with a disk containing both TMP and SMZ, but greater than 8% of such isolates from five of the other centers were resistant to the combination disk. A larger percentage of isolates of Klebsiella pneumoniae or Serratia marcescens were resistant, but the number varied from center to center. In the United States, resistance of human and animal isolates of Salmonella to the TMP-SMZ combination was almost completely absent, although greater than 50% of the animal isolates were resistant to sulfonamides. At a center that tested TMP and SMZ resistance with separate disks, resistance to TMP was found to be 30 times more common in sulfonamide-resistant than in sulfonamide-susceptible E. coli. This ratio may be useful as a monitor as treatment with TMP alone increases.

Bacteria↗
PubMedDate not supplied

Characterization of monoclonal and polyclonal antibodies to human tissue kallikrein.

Monoclonal antibodies to purified human urinary kallikrein have been developed. Selection of antibody producing clones was based on 125I-kallikrein binding activity of hybridoma media in both radioimmunoassay and enzyme-linked immunosorbent assay. Three clones (2 IgG1, 1 IgG2b) were subcloned, characterized, and compared with the polyclonal antiserum generated in rabbits immunized with the purified kallikrein. With radioimmunoassay, mouse ascitic fluids or rabbit antisera dilutions showing 50% binding to 125I-kallikrein were 1:1.2 X 10(6) (E7A9), 1:1.2 X 10(5) (H6A6), 1:8.0 X 10(4) (E12H1), and 1:1.4 X 10(6) (the rabbit antisera). With enzyme-linked immunosorbent assay, mouse ascitic fluids from clones E7A9 and H6A6 showed half-maximal absorbance at dilutions of 1:2.1 X 10(5) and 1:1.0 X 10(5) respectively, and the polyclonal antiserum showed half-maximal absorbance at a dilution of 1:2.0 X 10(4). These monoclonal antibodies showed no cross-reactivity with rat tissue kallikrein, rat urinary plasminogen activator, or dog pancreatic kallikrein, while the polyclonal antiserum showed some cross-reactivity. The binding of monoclonal or polyclonal antibodies to 125I-human urinary kallikrein was not affected by human plasma kallikrein, thrombin, or urokinase in a competitive radioimmunoassay. By using purified human urinary kallikrein immobilized to agarose, antibodies produced by clones E7A9 and H6A6 and in the rabbit antisera were purified to homogeneity. Each of these affinity-purified antibodies inhibited the esterase activity, and two of the three inhibited the kininogenase activity, of human urinary kallikrein. A sandwich immunosorbent assay was developed to measure this kallikrein using monoclonal antibody from the clone E7A9 in conjunction with the polyclonal antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗