Biomedical subjects

B Tiemann

Publications and source records attributed to B Tiemann.

15 recordsLinked to original sources

PubMed2005

Biocompatibility parameters in in-vitro simulated automated versus continuous ambulatory peritoneal dialysis.

BACKGROUND: In peritoneal dialysis, the usage of automated peritoneal dialysis (APD) has been steadily increased. As APD means larger volumes of solution and more frequent contact times with fresh dialysate, an additive negative impact on biocompatibility data, exceeding the known effect of conventional PD fluids, seems possible. For an in-vitro comparison of APD and CAPD, a new cell culture system has recently been established. METHODS: A double chamber cell culture system with human mesothelial cells on top of a permeable membrane and growth medium beyond was used for mimicking CAPD and APD. Reflecting the in vivo equilibration pattern, we compared an eight-hour CAPD with a CCPD setting, using a conventional PD solution. Cell viability was assessed with a MTT assay and cell function via constitutive and stimulated IL-6 release. CA125 was measured as a parameter of mesothelial cell integrity, and TGF-1beta was measured as an index of induction of fibrosis. RESULTS: Both the CAPD and the CCPD mode resulted in a significantly lower MTT assay and stimulated IL-6 release compared to growth medium. TGF-1beta and CA125 release did not differ between the PD modes and control. The CAPD and the CCPD mode itself did not differ with regard to MTT assay, IL-6 release, TGF-1beta and CA125 generation. CONCLUSION: From the in-vitro model imitating the acute exposure of mesothelial cells with conventional PD fluid in a CCPD and CAPD mode, there is no evidence that APD, due to the larger volumes of solution and more frequent contact times with fresh dialysate, has an acute, additive negative impact on biocompatibility parameters indicative for peritoneal host defense, mesothelial cell integrity and peritoneal fibrosis.

CA-125 Antigen↗

PubMed1999

Overexpression, purification, and partial characterization of ADP-ribosyltransferases modA and modB of bacteriophage T4.

There is increasing experimental evidence that ADP-ribosylation of host proteins is an important means to regulate gene expression of bacteriophage T4. Surprisingly, this phage codes for three different ADP-ribosyltransferases, gene products Alt, ModA, and ModB, modifying partially overlapping sets of host proteins. While gene product Alt already has been isolated as a recombinant protein and its action on host RNA polymerases and transcription regulation have been studied, the nucleotide sequences of the two mod genes was published only recently. Their mode of action in the course of the infection cycle and the consequences of the ADP-ribosylations catalyzed by these enzymes remain to be investigated. Here we describe the cloning of the genes, the overexpression, purification, and partial characterization of ADP-ribosyltransferases ModA and ModB. Both proteins seem to act independently, and the ADP-ribosyl moieties are transferred to different sets of host proteins. While gene product ModA, similarly to the Alt protein, acts also on the alpha-subunit of host RNA polymerase, the ModB activity serves another set of proteins, one of which was identified as the S1 protein associated with the 30S subunit of the E. coli ribosomes.

Amino Acid Sequence↗

PubMed1997

ADP-ribosylation and early transcription regulation by bacteriophage T4.

Bacteriophage T4 codes at least for two ADP-ribosylating activities, the 76 kDa Alt and the 24 kDa Mod gene products. The main target for both enzymes is the host RNA polymerase. We cloned and sequenced the alt gene and overexpressed the corresponding enzyme. The recombinant protein shows ADP-ribosylating activities in vitro, as had been described earlier for the native enzyme isolated from phage heads. The native as well as the recombinant protein ADP-ribosylate the alpha-subunit of RNA polymerase, but also subunits beta, beta' and sigma 70 and perform an autoribosylation reaction. Taking advantage of the pKWIII test system, constructed to measure promoter strengths in vivo, it was found that ADP-ribosylation of RNA polymerase leads to an increase of transcription from T4 early promoters up to a factor of two. In an infected host cell this should cause an enhanced expression of T4 genes. Depending on whether RNA polymerase was ADP-ribosylated or not, it initiated transcription at T4 promoters with different sequence characteristics: unribosylated RNA polymerase recognizes the early T4 promoters by an extended -10 region, whereas the ribosylated enzyme selects for T4 early promoters with an extended T4-specific and highly conserved -35 region. These results may reflect how the virus, step by step imposes its genetic program on the host cell, and in part they give a rationale for the extension of the consensus sequence observed with these promoters. We also sequenced the genomic region of the T4 mod gene and found two open reading frames coding both for proteins of approximately 24 kDa. Up to now none of the reading frames could be cloned into E. coli in an active form, making it highly probable that the ADP-ribosylation pattern inflicted by gene product Mod on host RNA polymerase is deleterious to these bacteria. Comparisons of the amino acid sequences showed significant homologies among the two reading frames. Computer analysis reveals that both Mod sequences and also the sequence of the Alt protein exhibit a structural concordance with the catalytic domains of other prokaryotic ADP-mono-ribosyltransferases such as the Pseudomonas aeruginosa exotoxin A, the cholera labile enterotoxin, the diphteria toxin, the heat labile enterotoxin A of E. coli, and pertussis toxin. We present a detailed model for T4 transcription regulation.

Adenosine Diphosphate↗

PubMed1996

Structure of the gene encoding nitrilase 1 from Arabidopsis thaliana.

The nitrilases of Arabidopsis thaliana (At) catalyze the conversion of indole-3-acetonitrile (IAN) to indole-3-acetic acid (IAA), thus controlling the last step of auxin biosynthesis. A full-length genomic clone encoding the complete cluster of the At nitrilases 1 to 3 (NIT1-3), including the respective promoter regions, has been isolated and the NIT1 isoform has been sequenced. The coding region (nit1) spans about 2.3 kb and is composed of five exons separated by four introns. The exon-intron splice junctions agree with the consensus sequences typical for plant genes. In agreement with the known cDNA sequence, the exons encode a protein of 346 amino acids (aa) with a deduced molecular mass of 38.2 kDa. The transcription start point (tsp) of nit1 was determined by primer extension experiments. This tsp defines a 5' untranslated region of 36 bp and is located 32 bp downstream from a TATA box. The promoter region of nit1 is located within the approx. 1.5-kb intergenic part that separates the nit2 and nit1 coding sections.

Aminohydrolases↗

PubMed1991

Ambulatory blood pressure and Holter monitoring during tennis play.

The effect of tennis play on blood pressure, heart rate response, and rhythm disturbances was evaluated in 21 men 39 to 61 years of age (M = 49.5 +/- 6.7 yrs). A Holter monitor was utilized for continuous ECG recording during tennis play and a portable ambulatory blood pressure recorder (Spacelabs) was used to measure blood pressures and heart rates periodically during tennis matches. The results indicated that blood pressure response to tennis (singles), although an activity of moderate aerobic intensity, can exert significant increases in systolic and diastolic blood pressure even in those persons who are normotensive at rest. Excessive body weight, and particularly abdominal deposition, appears associated with an increase in diastolic blood pressure to exercise. Few heart rhythm disturbances of consequence were uncovered. A simple submaximal step test such as the Canadian Aerobic Fitness Test, with ECG monitoring, could assist in detecting those individuals susceptible to an exaggerated blood pressure response and to heart rhythm disturbances at exercise.

Adult↗

PubMed1980