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Biomedical subjects

G Richter

Publications and source records attributed to G Richter.

At least 91 records · Page 5Linked to original sources
PubMed1997

Biosynthesis of riboflavin: characterization of the bifunctional deaminase-reductase of Escherichia coli and Bacillus subtilis.

The ribG gene at the 5' end of the riboflavin operon of Bacillus subtilis and a reading frame at 442 kb on the Escherichia coli chromosome (subsequently designated ribD) show similarity with deoxycytidylate deaminase and with the RIB7 gene of Saccharomyces cerevisiae. The ribG gene of B. subtilis and the ribD gene of E. coli were expressed in recombinant E. coli strains and were shown to code for bifunctional proteins catalyzing the second and third steps in the biosynthesis of riboflavin, i.e., the deamination of 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (deaminase) and the subsequent reduction of the ribosyl side chain (reductase). The recombinant proteins specified by the ribD gene of E. coli and the ribG gene of B. subtilis were purified to homogeneity. NADH as well as NADPH can be used as a cosubstrate for the reductase of both microorganisms under study. Expression of the N-terminal or C-terminal part of the RibG protein yielded proteins with deaminase or reductase activity, respectively; however, the truncated proteins were rather unstable.

Amino Acid Sequence↗
PubMed1997

Sibship size, sibship position, parental rearing and psychopathological manifestations in adults: preliminary analysis.

Almost all investigations concerning the relationships between sibship size, sibship position and psychiatric disorders addressed more formal aspects, i.e. frequency and position, with contradictory and inconsistent results. Analyses considering sibship size and birth order as mediating factors between parental rearing and psychopathological manifestations in adults are lacking. The present results of an investigation of 1,013 psychiatric inpatients and 251 healthy volunteers support a systematic association between sibship size and parental rearing, mainly in terms of a reversed relationship between emotional warmth, overprotection and number of siblings. An excess of psychiatric patients in the middle position of a sibling seems to be related to specific unfavourable rearing patterns. A validation of our preliminary results would be required in terms of preventive measures for children of risk populations.

Adult↗
PubMed1997

Assessment of bleeding for the evaluation of therapeutic preparations in small animal models of antibody-induced hemophilia and von Willebrand disease.

Three small animal models of bleeding are described and used to evaluate the effects of preparations intended for therapy of human bleeding disorders. We modified techniques for the assessment of bleeding to be able to reproducibly quantify blood loss and rate of blood flow in addition to the measurement of bleeding time. Temporary hemophilia was induced in a rabbit model by injection of high titer human inhibitor plasma [> or = 1000 Bethesda units (BU)/ml]. A decrease in rabbit FVIII from normal values to below the limit of detection was observed within 30 min, cuticle bleeding time changed from normal (approx. 10 min) to steady state bleeding (> 30 min), and the rate of blood flow increased from 4 to > 30 microliters blood/min. Infusion of an activated prothrombin complex concentrate, (FEIBA STIM4, Immuno) at doses between 75 and 150 U/kg normalized the rate of blood flow, while infusion of FVIII/vWF concentrate resulted in partial correction. Administration of FVIIa, both recombinant and plasma-derived, failed to correct bleeding, however. In an analogous murine model, FVIII/ vWF inhibitor plasma was obtained by immunizing goats with a purified human FVIII/vWF complex. This plasma cross-reacted with mouse vWF in vitro. Injection of the anti-FVIII/vWF inhibitor plasma into mice caused a decrease in vWF antigen, in some animals with a complete loss of vWF multimers comparable to severe von Willebrand disease. A specific anti-vWF inhibitor plasma obtained by immunization of goats with recombinant vWF was used in a further murine model, resulting in a gradual but substantial decrease in FVIII as well as in intensive bleeding. The infusion of a FVIII/vWF concentrate (IMMUNATE, IMMUNO) normalized the rate of blood flow in both murine models. The same assessment methods were used to characterize bleeding in a natural mouse model of von Willebrand disease (strain RIIIS/J). The use of quantitative techniques of assessment of blood loss and rate of blood flow appears to be a helpful tool for characterizing hemorrhagic situations and evaluating the capacity of therapeutic preparations to correct hemostatic defects.

Animals↗
PubMed1996

Biosynthesis of riboflavin. Lumazine synthase of Escherichia coli.

A gene located at 443 kilobases on the Escherichia coli chromosome (subsequently designated ribE) was expressed in a recombinant E. coli strain and was shown to code for the enzyme 6, 7-dimethyl-8-ribityllumazine synthase. The recombinant enzyme was purified to homogeneity. The protein is an icosahedral capsid of 60 subunits with a mass of about 1 MDa as shown by hydrodynamic studies and by electron microscopy. In contrast to the icosahedral lumazine synthase-riboflavin synthase complex of Bacillus subtilis, the lumazine synthase of E. coli is not physically associated with another enzyme of the riboflavin pathway, and the core of the icosahedral capsid is empty. The RIB4 gene of Saccharomyces cerevisiae was also expressed to a high level (about 40% of cellular protein) in E. coli. The recombinant protein is a pentamer of 90 kDa. An insertion of 4 amino acids into helix alpha4 is likely to hinder the formation of an icosahedral capsid by the yeast protein. The kinetic properties of lumazine synthase of E. coli, B. subtilis, and S. cerevisiae are similar.

Amino Acid Sequence↗
PubMed1996

Cloning, sequencing, mapping and hyperexpression of the ribC gene coding for riboflavin synthase of Escherichia coli.

The gene coding for riboflavin synthase of Escherichia coli has been cloned by marker rescue on a 6-kb fragment that has been sequenced. The riboflavin synthase gene is identical to the ribC locus and codes for a protein of 213 amino acids with a mass of 23.4 kDa. It was mapped to a position at 37.5 min on the physical map of the E. coli chromosome. The 3' end of the ribC gene is directly adjacent to the cfa gene, which codes for cyclopropane-fatty-acid synthase. This gene is followed by two open reading frames designated ydhC and ydhB, which are predicted to code for putative proteins with 403 amino acids and 310 amino acids, respectively. The gene ydhC is similar to genes coding for resistance against various antibiotics (cmlA, bcr) and probably codes for a transmembrane protein. The protein specified by ydhB shows sequence similarity to a large family of DNA-binding proteins and probably represents a helix-turn-helix protein. The ydhB gene is directly adjacent to the regulatory gene purR. A 288-bp segment of the cfa gene has earlier been mapped incorrectly to a position adjacent to greA at 67 min. The ribC gene was hyperexpressed in recombinant E. coli strains to a level of about 30% of cellular protein. The protein was purified to homogeneity by chromatography. The specific activity was 26000 nmol.mg-1.h-1. The protein sediments at a velocity of S20 = 3.8 S. Sedimentation-equilibrium centrifugation indicated a molecular mass of 70 kDa, consistent with a trimer structure. The primary structure of riboflavin synthase is characterized by internal sequence similarity (25 identical amino acids in the C-terminal and N-terminal parts suggesting two structurally similar folding domains.

Amino Acid Sequence↗
PubMed1996

Human fetal gene therapy: moral and ethical questions.

This two-part paper discusses moral and ethical questions raised by future trials of human fetal gene therapy. The first part examines broad moral issues to explore whether fetal gene therapy is a morally praiseworthy goal. Ought it be done at all? These issues include (i) how the concept of fetal gene therapy originally arose as a goal envisioned at the beginning of prenatal diagnosis, (ii) preimplantation genetic diagnosis as a better preconceptual alternative for parents at higher genetic risk, (iii) alternatives to genetic abortions, (iv) the social and economic priority of fetal gene therapy, and (v) whether fetal gene therapy is a "slippery slope" that will end in germ-line gene therapy. This part concludes that far more reasons exist to commend fetal gene therapy than to reject it, given its limits and modest social and economic priority. The second part responds to specific ethical questions that must be raised about any protocol for human gene therapy. These questions and issues are adapted to the prenatal situation: (i) how the previable fetus becomes a "patient," (ii) concern for clinical benefit and minimizing risks to the fetus and pregnant woman, (iii) concern for the voluntary and informed participation of the pregnant woman, the father, and for protection of their privacy, (iv) concern for fair selection of subjects, (v) considerations of harm to germ line cells, and (vi) the role of public oversight of fetal gene therapy. The article concludes by recommending a continuation of the consolidated Recombinant Advisory Committee (RAC) for the near future.

Abortion, Spontaneous↗
PubMed1996

Phenprocoumon for prevention of shunt occlusion after transjugular intrahepatic portosystemic stent shunt: a randomized trial.

Development of stenosis or occlusion of the transjugular intrahepatic portosystemic stent shunt (TIPSS) is one of the major limiting factors in the long-term viability of this procedure. The efficacy of anticoagulation with heparin which is used in different centers is still unclear. In the present study, we evaluated the effect of phenprocoumon on shunt patency after TIPSS placement using Palmaz stents; 49 patients with Child's A and B cirrhosis, who underwent successful TIPSS placement were randomized into the treatment group (n = 24) who received phenprocoumon and a control group (n = 25). After 11 to 13 weeks, all patients were admitted and had a reevaluation that included control angiography by transjugular approach. Phenprocoumon treatment was stopped after the first reevaluation and both groups were followed for 1 year after randomization. During the 3-month treatment period 11 of 22 patients of the treatment group and 12 of 23 patients of the control group required reintervention because of an increased portosystemic gradient. Five of the 12 patients in the control group showed complete occlusion of the shunt, whereas no occlusion in the treatment group was observed (P < .05). During the mean follow-up of 8 months after the treatment was stopped, in both groups stenosis occurred in 50% of patients, but no further occlusion of the stent was observed. These data indicate that occlusion of the stent is related to thrombosis, whereas stenosis does not appear to be dependent on blood coagulation. In patients with preserved liver function occlusion of the shunt may be prevented by phenprocoumon treatment in the first 3 months after TIPSS placement. Thereafter shunt occlusion was not observed and further phenprocoumon treatment seemed unnecessary.

Anticoagulants↗
PubMed1996

Regulation of an embryogenic carrot gene (DC 2.15) and identification of its active promoter sites.

According to previous studies the expression of the gene DC 2.15 is induced in cultured carrot cells after a transfer to an auxin-free medium, where somatic embryo development occurs. This embryogenic gene encodes a prolinerich protein, which resembles proteins involved in auxin-controlled developmental processes. To understand the mechanism underlying the regulation of DC 2.15, an experimental approach has been employed which allows the direct identification of the DC 2.15 promoter structure by applying PCR techniques. We demonstrate the presence of five distinct promoter sequences highly similar in structure, but slightly different in a common region of about 15 nucleotides, which contain the binding site for the GATA factor originally found in the human HOX gene. Activity of each promoter structure was assessed in developing somatic embryos containing the specific sequence fused to the beta-glucuronidase (GUS) reporter gene. For two of the five promoter structures a drastic increase in activity was registered during the torpedo stage while the remaining three were inactive throughout the stages of somatic embryogenesis.

Base Sequence↗
PubMed1996

[Dental materials--problem substances in allergologic diagnosis? I: Analysis of test results in patients with mouth mucosa/dental material problems].

Patch testing as a part of the diagnostic evaluation of patients suffering from oral mucosal complaints or with symptoms where dental materials are suspected to be the cause is hampered by numerous difficulties. The ingredients of denture materials as well as their liberation in the oral cavity are often unknown. Contact with many of the potential ingredients of denture materials can occur on other occasions, as well, thus making it difficult to find out where the patient has acquired his or her sensitization. The special morphological and immunological situation in the oral mucosa may produce tolerance of substances which evoke a positive patch test reaction on the skin of the back. This paper introduces the possible spectrum of allergens in these patients and discusses the difficulties in the assessment of the relevance of positive patch test reactions. From August 1992 to July 1994, 756 patients with complaints of the oral mucosa and/or suspected contact allergy to denture materials were patch tested in the departments of dermatology joining the Information Network of Departments of Dermatology in Germany (IVDK). Among these patients, women were overrepresented, while individuals with atopic dermatitis were underrepresented. The allergen spectrum included amalgam, mercury compounds, gold salts, palladium chloride and methyl methacrylate. However, the epidemiological value of these data is limited. A second part of this paper will review the various groups of allergens.

Adult↗
PubMed1996

[Dental materials--problem substances in allergologic diagnosis? II: Patch test diagnosis and relevance evaluation of selected dental material groups].

The problems in patch testing and relevance evaluation as well as the practical consequences are discussed for the most important groups of dental materials (DM). These include metal alloys: amalgam with a low allergy prevalence; palladium salts showing a high correlation with nickel allergy but a low one with metallic palladium or alloys; the widespread allergen nickel is most relevant when dealing with nickel containing DM-alloys that are not corrosionresistant; gold salts with widely differing test results and limited benefit to detect genuine gold intolerance. Among synthetic resins methylmethacrylate is the most important allergen because of the high frequency of exposition. With composite materials and other methacrylates, both cross reactions and active sensitization should be kept in mind. Relevant reactions due to additives are rare; positive benzoylperoxide tests should be interpreted very critically. A number of DM may contain allergens of the etheric oils-colophonium - Perubalsam group. DM should be tested with standardized methods only. As the dental consequences may be expensive, interpretation of such test results demands utmost care and special experience.

Adult↗
PubMed1996

Regulation of the Arabidopsis thaliana aquaporin gene AthH2 (PIP1b).

Arabidopsis thaliana was transformed with constructs composed of the aquaporin AthH2 promoter and the coding sequence of beta-glucuronidase (GUS) as reporter gene. The transgenic plants obtained were treated with different light qualities or phytohormones and the activity of the AthH2 promoter was determined in situ using a specific GUS assay. With blue light (400-550 nm) and white light, significant activation of the promoter was observed. The same was true for the application of gibberellic acid (GA) and abscisic acid (ABA). In contrast, red light and indole-3-acetic acid (IAA) had only minor effects on the promoter activity. The significance of sequence elements with relation to GA or ABA was confirmed by deletion analyses of the AthH2 promoter. Likewise, a promoter segment with importance for hydathoid specific expression was identified.

Arabidopsis↗
PubMed1996

Response to "Germ-line therapy to cure mitochondrial disease: protocol and ethics of in vitro ovum nuclear transplantation" by Donald S. Rubenstein, David C. Thomasma, Eric A. Schon, and Michael J. Zinaman (CQ Vol 4, No 3)

As a result of the dramatic advances made in molecular biology, gene therapy has become viable. The initial endeavors were with monogenetic disorders, but gene therapy may also be of benefit in cancer therapy and treatment of infectious diseases. The current framework for the ethical discussion of gene therapy is a two-dimensional scheme. The first dimension is the target tissue (somatic cells versus germ-line cells) and the second dimension is the purpose (therapy/prevention versus enhancement). Although the mitochondrial genome occurs in eukaryotic cells at several hundred copies and the sequence has been known since the late 1980s, it has been excluded from the ethical discussions of gene therapy or genetic interventions. With the development of the first IVONT protocol and successful experiments with mitochondrial transfection vectors, the two-dimensional framework is no longer adequate. Therefore, we propose a three-dimensional framework for the ethical debate of genetic interventions in humans, whereby we include the genome type (nDNA versus mtDNA) as a third dimension. The ethical evaluation of all imaginable genetic interventions is located on five different levels. The demands for ethical justification are different for each.

DNA↗
PubMed1996

[Therapeutic efficiency of of pulsed spray lysis in peripheral arterial occlusions].

PURPOSE: To determine the clinical efficacy of pulse-spray thrombolysis. MATERIAL AND METHODS: In a prospective trial 28 patients with acute arterial (n = 14) and bypass (n = 14) occlusions of the lower extremities were treated with pulse spray thrombolysis. 23/28 legs were at risk. RESULTS: Technical and clinical success were 89% and 68% respectively. Time interval until restitution of antegrade flow was less than two hours, the median duration of the complete intervention was 17 hours. Two patients (7.1%) needed transfusions for inguinal haematomas. After six months 50% of occluded segments remained patent, secondary patency is comparable at 53%. Bypasses show significantly lower patency (p = 0.04) and higher amputation (p = 0.009) rates than native arteries. Bad run-off (< or = 1 artery patent) is a significant predictor for clinical failure and early amputation. CONCLUSIONS: The distinct advantage of pulse-spray thrombolysis is fast restoration of antegrade flow and thereby effective treatment of acute ischaemia. The complication rate is low without associated mortality.

Adult↗