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Biomedical subjects

B Keller

Publications and source records attributed to B Keller.

At least 127 records · Page 7Linked to original sources
PubMed1984

Gene 68, a new bacteriophage T4 gene which codes for the 17K prohead core protein is involved in head size determination.

We have identified the gene for a major component of the prohead core of bacteriophage T4, the 17K protein. The gene, which we call gene 68, lies between genes 67 and 21 in the major cluster of T4 head genes. All of the genes in this region of the T4 genome have overlapping initiation and termination codons with the sequence T-A-A-T-G. We present the DNA sequence of the gene and show that it codes for a protein containing 141 amino acids with an acidic amino-terminal half and a basic carboxyl terminus. Antibodies prepared against the 17K protein were used to show that it is cleaved by the phage-coded gp21 protease during head maturation and that most of the protein leaves the head after cleavage. A frameshift mutation of the gene was constructed in vitro and recombined back into the phage genome. The mutated phages had a drastically reduced burst size and about half of the particles produced were morphologically abnormal, having isometric rather than prolate heads. Thus, the 17K protein is involved in head shape determination but is only semi-essential for T4 growth.

Amino Acid Sequence↗
PubMed1984

Isolation of the prohead core of bacteriophage T4 after cross-linking and determination of protein composition.

The naked core of bacteriophage T4 was isolated ex vivo after cross-linking with either glutaraldehyde or dithiobis(succinimidyl propionate). The isolated particles appeared to be morphologically identical to the cores found in thin sections, to those demonstrated in in situ lysis preparations, and to core structures assembled in vitro. Treatment with glutaraldehyde provided core particles which were morphologically well preserved, whereas dithiobis(succinimidyl propionate)-induced cross-linking was reversible and allowed analysis of the protein composition of the isolated particles. The identity of the reversibly cross-linked particles with those obtained after irreversible cross-linking was suggested by their morphology and their similar sedimentation behavior. Immunolabeling confirmed the structural presence of the main core protein in both structures. Gel electrophoresis of reversibly cross-linked cores revealed the essential head proteins gp22, gp67, and gp21, the three internal proteins IPI, IPII, and IPIII, and a 17K protein.

Antibodies, Viral↗
PubMed1983

[Breakfast tolerance test: application to the detection of gestational diabetes].

There is general agreement that diagnosis of diabetes mellitus in pregnancy is requisite but the means of achieving it are still under discussion. The plasma glucose, insulin and C peptide responses to an oral glucose tolerance test were compared with the intravenous glucose tolerance test and a standardized breakfast tolerance test in 26 pregnant women, in order to define a simple diagnostic criterion for gestational glucose intolerance. The results of the oral glucose tolerance test distinguished between a group of 19 normal women and a group of 7 diabetic women with abnormal glucose tolerance tests. The breakfast tolerance test used (84 g carbohydrates, 22,6 g protein, 9,4 g fat, 690 calories) was followed by blood glucose modifications very similar to those observed with the oral glucose tolerance test, but the insulin response was significantly greater. The consistency between the breakfast tolerance and intravenous glucose tolerance tests was confirmed by the existence of correlations between the glucose area of the breakfast tolerance test and the coefficient K in the two groups studied. Our results suggest that the breakfast tolerance test could be as sensitive as the oral glucose tolerance test for detecting glucose intolerance; the most discriminative glycemic value appeared to be that at the 180 th minute, usually under 1 g/l in the normal pregnant women. This test could be proposed as an easy and economic method for diagnosing gestational diabetes. These preliminary results require confirmation by a study in a larger population.

Administration, Oral↗
PubMed1983

Tetrodotoxin-sensitive and -resistant effects of veratridine on the noradrenergic neurone of the rat vas deferens.

The veratridine-induced release of 3H-noradrenaline from noradrenergic neurones was examined in the isolated vas deferens of either untreated or reserpine plus pargyline-pretreated rats. The rat vas deferens, whose catechol O-methyltransferase was inhibited, was first incubated with 0.4 mumol/l 3H-(-)noradrenaline (30 min) and then washed repeatedly with amine-free solution. After 120 min (i.e., well after the efflux of tritium from the tissue had reached a steady level and was predominantly of neuronal origin), washout was continued in the presence of veratridine for further 10-15 min. In vasa deferentia of untreated rats, veratridine (1-100 mumol/l) caused a concentration-dependent increase in the efflux of tritium. At high concentrations of the drug (30 or 100 mumol/l), this increase in efflux was peak-like during the first 3 min ("peak response") and then fell to a plateau ("plateau response"). In the presence of veratridine, unchanged 3H-noradrenaline accounted for about 75% of the tritium efflux (the rest being represented by deaminated 3H-catechol metabolites). The "peak response" to veratridine (100 mumol/l) was abolished by tetrodotoxin (TTX; 1 mumol/l) or the absence of external Ca2+. Cocaine (10 mumol/l) affected neither the "peak response" as such nor the contribution by 3H-noradrenaline to the efflux of tritium during that response. Hence, the "peak response" was due to exocytotic release of 3H-noradrenaline from the neurone. The "plateau response" to veratridine (100 mumol/l) was unaffected by the absence of external Ca2+, largely resistant to TTX (1 mumol/l) and moderately reduced by cocaine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

[Biosynthesis of phenylalanine and tyrosine in Flavobacteria].

The enzymes of the terminal steps of phenylalanine and tyrosine biosynthesis, chorismate mutase, prephenate dehydratase, arogenate dehydratase, prephenate dehydrogenase and arogenate dehydrogenase, were studied in 11 different species of the genus Flavobacteria. A comparison of the specific activities, cofactor specificity and regulation of the enzymes, allows a differentiation within the Flavobacteria. All strains studied utilize both arogenate and p-hydroxyphenylpyruvate as an intermediate in L-tyrosine synthesis. Phenylpyruvate was found to be the precursor of phenylalanine in most bacteria. No feedback inhibition of arogenate dehydrogenase by phenylalanine and tyrosine was observed. The diverse strains of the flavobacteria were found to possess different regulatory patterns with respect to the action of phenylalanine and tyrosine on the other enzymes. On the basis of these results a tentative classification of the Flavobacteria within the two groups formed by the different DNA base ratios is proposed.

Chemical Phenomena↗
PubMed1983

[Biosynthesis of phenylalanine and tyrosine in Streptomycetes].

The biosynthesis of phenylalanine and tyrosine from prephenic acid may proceed via phenylpyruvic acid or p-hydroxyphenylpyruvic acid or via arogenate. The enzymes necessary for these biosynthetic steps have been tested in a variety of Streptomycetes. Tyrosine is synthesized exclusively via arogenate, while phenylalanine is synthesized via phenylpyruvic acid. The feedback inhibition pattern of the corresponding enzymes has been determined. The organisms may be divided into four groups according to the properties of the phenylalanine and tyrosine biosynthetic enzymes and their regulation patterns.

Feedback↗
PubMed1982

Arogenate (pretyrosine) pathway of tyrosine and phenylalanine biosynthesis in Pseudomonas aureofaciens ATCC 15926.

Assays of enzyme activities suggest that arogenate, the product of prephenate transamination, is an intermediate in the biosynthesis of both phenylalanine and tyrosine in Pseudomonas aureofaciens ATCC 15926. In addition to prephenate dehydratase and prephenate dehydrogenase, arogenate dehydratase and arogenate dehydrogenase activities were demonstrated. This pattern of aromatic amino acid biosynthesis in pseudomonads had previously been demonstrated only in P. aeruginosa. Arogenate dehydrogenase from P. aureofaciens differs from that in P. aeruginosa in its utilization of either NAD+ or NADP+ as cofactor and its inhibition by L-tyrosine. During ammonium sulphate fractionation, arogenate dehydratase co-precipitated with prephenate dehydratase I activity and not with prephenate dehydratase II. The pattern of regulation of the arogenate route to tyrosine in P. aureofaciens ATCC 15926 differed from that previously reported for strain ATCC 13986.

Amino Acids, Dicarboxylic↗
PubMed1981

Nature of macrophage-T cell interaction in secondary helper cell generation in vitro. Genetic restriction of macrophage-T cell interaction, which determines T-B genetic restriction.

To investigate the histocompatibility requirements for the macrophage-T cell interaction in the secondary antibody response, splenic T cells from antigen (carrier)-primed F1 hybrid mice were restimulated in vitro with carrier-pulsed F1, parental or allogeneic macrophages. Surviving T cell were cocultured with hapten-primed F1 or parental "B cells" and restimulated with the appropriate hapten-carrier conjugate. The IgG antibody-forming cell response was then measured using a plaque assay. Mapping of the genetic restriction was performed by use of different strain combinations. T helper cells could be restimulated in the presence of macrophages only provided they shared the I-A subregion of the major histocompatibility complex with the F1 T cells frm F1 hybrids restimulated with parental or I-A-identical macrophages were shown to only cooperate with parental B cells of the same I-A haplotype as the macrophages used for restimulation. The defect was at the level of the macrophage, as addition of macrophages of the I-A haplotype used for the restimulation culture reconstituted ability of F1 helper cells to cooperate with the I-A-nonidentical B cells.

Animals↗
PubMed1977

[Metabolism of hexobarbital in patients with acute hepatitis and cirrhosis (author's transl)].

16 patients with acute hepatitis, 18 patients with cirrhosis and a total of 21 volunteers and patients with normal liver function received 7.32 mg/kg hexobarbital by linear intravenous infusion within 60 min. Hexobarbital was determined gaschromatographically in serial blood samples and the hexobarbital-clearance was calculated from the plasma concentration curve versus time. Additional experiments were performed in rats suffering from so called "galactosamine hepatitis". In half of the patients with acute hepatitis a normal hexobarbital clearance could be found. In the other patients this was distinctly reduced but not correlation was found to other liver function tests. Patients with cirrhosis were subdivided into two groups. The patients in group 1 were well compensated. The patients in group 2 had a decompensated state with ascites and oesophageal varices. In nearly all patients with cirrhosis the hexobarbital-clearance was diminished. This was more pronounced in group 2. Ketohexobarbital excretion in healthy subjects was in the range of 40-60% of dose. Patients with acute hepatitis excreted only 10-20% of dose and patients with liver cirrhosis only about 5% of dose. In rats with "galactosamine hepatitis" hexobarbital clearance in vivo was distinctly reduced and this could be explained by diminished microsomal cytochrome p 45- and hexobarbital oxidation rate.

Acute Disease↗