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Biomedical subjects

J Schumann

Publications and source records attributed to J Schumann.

At least 37 records · Page 2Linked to original sources
PubMed1993

Stabilization of creatinase from Pseudomonas putida by random mutagenesis.

Creatinase (creatine amidinohydrolase, EC 3.5.3.3) from Pseudomonas putida is a homodimer of 45 kDa subunit molecular mass, the three-dimensional structure of which is known at 1.9 A resolution. Three point mutants, A109V, V355M, and V182I, as well as one double mutant combining A109V and V355M, and the triple mutant with all three replacements, were compared with wild-type creatinase regarding their physical and enzymological properties. High-resolution crystal data for wild-type creatinase and the first two mutants suggest isomorphism at least for these three proteins (R. Huber, pers. comm.). Physicochemical measurements confirm this prediction, showing that the mutations have no effect either on the quaternary structure and gross conformation or the catalytic properties as compared to wild-type creatinase. The replacement of V182 (at the solvent-exposed end of the first helix of the C-terminal domain) does not cause significant differences in comparison with the wild-type enzyme. The other point mutations stabilize the first step in the biphasic denaturation transition without affecting the second one. In sum, the enhanced stability seems to reflect slight improvements in the local packing without creating new well-defined bonds. The increase in hydrophobicity generated by the introduction of additional methyl groups (A109V, V182I) must be compensated by minor readjustments of the global structure. Secondary or quaternary interactions are not affected. In going from single to double and triple mutants, to a first approximation, the increments of stabilization are additive.

Cloning, Molecular↗
PubMed1993

Nucleotide sequence and homology comparison of two genes of the sulfate transport operon from the cyanobacterium Synechocystis sp. PCC 6803.

The genome of Synechocystis sp. PCC 6803 contains an operon with homology to the sulfate permease of other prokaryotes. We used antibodies raised against cytoplasmic membrane protein to find three genes with strong homology to sbpA, orf81 and cysT genes of the cyanobacterium Synechococcus sp. PCC 7942, Escherichia coli, Salmonella typhimurium and Marchantia polymorpha. It is likely that the permease genes are expressed and the proteins are inserted into the cytoplasmic membrane.

Amino Acid Sequence↗
PubMed1993

Intrinsic stability and extrinsic stabilization of creatinase from Pseudomonas putida.

Creatinase (creatine amidinohydrolase, EC 3.5.3.3), a homodimer of 45 kDa subunit molecular mass, shows only limited functional stability, and is inaccessible to reconstitution after preceding deactivation, denaturation and dissociation. The enzyme has been characterized regarding its native and denatured states. Studying its unfolding characteristics in the presence of "extrinsic factors", such as DTE, BSA and glycerol, it was possible to define solvent conditions where the stability of the enzyme is significantly improved. Apart from protecting essential thiol groups and charge screening effects, the stabilization is caused mainly by preferential solvation. In the presence of 20% (w/v) glycerol, the kinetic analysis of the time course of denaturation indicates that a partially active folding intermediate, rather than the whole molecule, is involved in the stabilization. The mixed solvent improves the thermal stability, as well as the stability toward GdmCl and urea.

Circular Dichroism↗
PubMed1991

Topographical and enzymatic characterization of amylases from the extremely thermophilic eubacterium Thermotoga maritima.

The hyperthermophilic eubacterium Thermotoga maritima uses starch as a substrate, without releasing amylase activity into the culture medium. The enzyme is associated with the 'toga'. Its expression level is too low to allow the isolation of the pure enzyme. Using cycloheptaamylose and acarbose affinity chromatography and common chromatographic procedures, two enzyme fractions are obtained. They differ in specificity, pH-optimum, temperature dependence and stability. Substrate specificity and Ca2+ dependence indicate alpha-, beta- and gluco-amylase activity. Compared with alpha-amylase from Bacillus licheniformis (Tmax = 75 degrees C), the amylases from Thermotoga maritima show exceedingly high thermal stability with an upper temperature limit at 95 degrees C. Significant turnover occurs only between 70 and 100 degrees C, i.e. in the range of viability of the microorganism.

Amylases↗
PubMed1991

The relationship between characteristics of the tumor cells and sex of the patients in primary malignant melanomas.

Sex is a well proven prognosticator in primary malignant melanoma. We studied 19 parameters of tumor cells in primary malignant melanoma from 391 patients, the purpose being to determine if melanomas in men and women are alike. Apart from results in thin melanomas, no difference was seen between the sex groups. Thin melanomas showed a significant difference for the melanoma-associated antigen G7-E2 (higher expression in women) and the histocompatibility antigen HLA-DR (higher expression in men). The results suggest that sex-related prognostic differences are due more to host than to tumor characteristics.

Antigens, Neoplasm↗
PubMed1991

Flow sorting of tumor cells for morphometric analysis, particularly of rare cells.

Using flow cytometric DNA measurement and sorting combined with morphometric light microscopy, different groups of cells were studied in a human melanoma pleural effusion, a human melanoma lymph node metastasis and a mouse tumor, as well as in normal reference tissues. Beside cells of the predominant tumor cell population, three types of rare tumor cells were studied after enrichment by sorting: a) giant cells from the greater than 8c region, comprising about 5% of the tumor cells, b) binucleated and multinucleated cells with unequal nuclear sizes within the same cell, found at frequencies of about 1.5%, and c) less than 2c cells which were derived from the so-called "debris"-region of the DNA histogram, found at frequencies of about 1 to 6%. All these rare cells were found only in the malignant tumors and not in the benign reference tissues. Morphometry showed that the increase in the cellular DNA content in the different fractions of tumor cells was combined with an increase in the cellular and nuclear sizes. However, the n/c-ratio was constant in the whole range of tumor cell fractions, including the fractions from the the less than 2c and the greater than 8c regions. The n/c-ratio of the less than 2c cells and giant cells differed from that of corresponding normal cells underlining their origin from the predominant tumor cell population. The possible linkage between the occurrence of the three rare cell types and genetic instability of tumors related to faulty nucleus and cell division is discussed.

Animals↗
PubMed1991

DNA flow cytometry in the prognosis of primary malignant melanoma.

DNA flow cytometry was carried out on 804 primary melanomas. The data were analyzed with a follow-up of 24-96 months. 57% of the cases were diploid, 32% had one abnormal cell population, and 11% were multiclonal. In 8% of the aneuploid tumors there were cell lines in the hypertetraploid range. A reliable S phase determination was possible in 524 cases. Among these 11% had an S phase exceeding 15%. Using an increased tumor thickness, relapse rate and mortality as criteria of tumor progression, aneuploidy and multiclonality, the occurrence of hypertetraploid cell lines and a high S phase (greater than 15%) proved to be correlated with a poor prognosis.

Adolescent↗
PubMed1991

Sequential DNA flow cytometry in metastatic malignant melanoma.

Sequential flow cytometry was performed on 73 metastatic malignant melanomas, derived from 804 primary tumors. Tumor thickness was confirmed an excellent prognostic parameter in primary melanoma, but did not allow reliable predictions in metastatic disease. Also, aneuploidy and genetic heterogeneity, both common in metastatic melanoma, were equally distributed among patients differing in survival time. However, a remarkable acceleration was observed in the generation of abnormal cell lines in patients dying early of metastatic disease.

DNA, Neoplasm↗
PubMed1990

The primary structure of the gamma-subunit of the ATPase from Synechocystis 6803.

The nucleotide sequence of the gene coding for the F0F1-ATPase gamma-subunit (atpC) from the transformable cyanobacterium Synchocystis 6083 has been determined. The deduced translation product consists of 314 amino acid residues and is highly homologous (72% identical residues) to the sequences of other cyanobacterial gamma-subunits. The Synechocystis 6803 sequence is also homologous to the chloroplast gamma-sequence. Like in the other cyanobacterial subunits, only the first of the 3 cysteine residues, which are involved in energy-linked functions of the gamma-subunit in spinach chloroplasts, is conserved in Synechocystis 6803.

Adenosine Triphosphatases↗
PubMed1990

Age-dependent proteins in eyes of annual killifishes Pterolebias longipinnis detected by 2-dimensional electrophoresis.

1. Eye proteins of Pterolebias longipinnis have been analyzed by 2-dimensional isoelectric focusing SDS-polyacrylamide gel electrophoresis during aging from adolescence until normal death. 2. The protein pattern on the gels changed gradually with progressing age. 3. In senescent eyes, three protein spots appeared for a time and 36 disappeared from the pattern. 4. The isoelectric points of the proteins in the presence of urea and the molecular weights in an unreducing buffer are presented.

Aging↗
PubMed1990

[Herpesvirus infections--indications for chemotherapy in dermato-venereology].

Specific antivirals like acyclovir have ameliorated the outcome of severe herpesvirus infections, especially in immunocompromised patients. Varicella can be prevented in high-risk patients after exposure by therapy with varicella-zoster immunoglobulin. Despite this favorable development, there are many unresolved problems in the management of herpesvirus infections, such as the use of acyclovir during pregnancy, the treatment of both motoric neuropathy and postherpetic neuralgia. Chemotherapy-resistant herpesvirus may cause severe syndromes in patients suffering from HIV infection or from iatrogenic immunosuppression. Isolation of resistant viruses provides the stimulus to establish tests of viral resistance and to use antiviral drugs more carefully.

Acyclovir↗
PubMed1989

Metastatic human melanoma. Phenotypic heterogeneity and antigen expression in relation to the clinical status.

According to animal experiments, metastasis to a particular organ depends on the phenotype of the tumor cells. Widespread metastatic dissemination including internal organs would therefore, at least in part, depend on the capacity of tumor cells to modulate, resulting in increased phenotypic heterogeneity. We found evidence for this assumption in human melanoma by phenotyping metastases (mainly cutaneous/subcutaneous) from 59 patients by the use of six monoclonal antibodies. Interlesional antigenic heterogeneity was present in 22/33 (67%) patients with disseminated metastases including at least one internal organ, but only in 4/26 (15%) patients whose metastases were restricted to skin and/or skin-draining lymph nodes (P less than or equal to 0.01). Chemotherapy cannot be the main reason for interlesional phenotypic heterogeneity, as seen by comparison of treated and untreated patients. Aneuploid melanoma metastases, as an indication for instability on the chromosomal level, were found in the majority of patients (84%) regardless of their clinical situation. Widespread disease was significantly related to the loss of the cytoplasmatic antigen K-1-2 and to the expression of the 130-kDa membrane antigen A-1-43.

Antigens, Neoplasm↗
PubMed1986

Flow cytometry as a tool for the prognostic assessment of human neoplasia.

Flow cytometry permits the quantitative description of neoplastic cell populations from the point of view of their cytogenetic and cytokinetic features. The advances in preparation of cellular monodispersed samples allow the examination not only of in vitro and hematological, but also of surgical, biopsy, endoscopic, and lavage specimens. The analysis of cytometric DNA content has evidenced the importance of (aneu)ploidy as a remarkable tumor marker. Tumors of different sites and, in some cases, stages and/or grades are characterized by a differential occurrence of diploid vs. aneuploid cell subpopulations and by the eventual presence of different stem cell lines within the same tumor. For certain classes of neoplasms, these parameters can be used for the early recognition of neoplasia and related to disease evolution and dissemination and to the results of therapy. Flow cytometry can also be used to evaluate the fraction of (cycling) cells in the S-phase and of proliferating cells (growth fraction). The percent of S cells can be extracted from cytometric DNA content histograms. Furthermore, the method of Bromodeoxyuridine (BrdUrd) incorporation has been recently introduced into flow cytometry. BrdUrd labeling in cycling cells can be detected either by the induction of quenching or enhancement of specific DNA-dye fluorescence or by fluorescent anti-BrdUrd monoclonal antibodies. This approach has been confirmed by preliminary comparative tests on cultured cells, normal and malignant bone marrow, and human solid tumor specimens. These parameters, together with other cytometric parameters of potential importance for the cellular characterization of malignancy, offer a reliable and real time-saving tool for the prognostic assessment of human tumors and the predicting and monitoring of the results of therapy.

Aneuploidy↗
PubMed1986

Considerations in the design of possible cell cycle effective drugs.

Antineoplastic agents are known to induce differential cytotoxic and cytostatic effects throughout the cell cycle. Many drugs have greater toxicity for cycling cells and act selectively at one or more phases of the cycle and may cause partial synchrony of surviving cells. However, these observations have been generally carried out on in vitro systems only and present a variety of complexities and pitfalls. Furthermore, human tumours are often characterized by a relatively low fraction of proliferating cells and present a large cellular heterogeneity as far as their cytogenetic, cytokinetic, and clonogenic features and their responses to drugs are concerned. Therefore, resistance to chemotherapy is due to various factors characterizing, in some instances, each individual tumour. In spite of the advent of technological advances such as flow cytometry, it is still difficult to design kinetic-orientated therapies especially for the treatment of solid tumours. Consequently, it is also difficult to design protocols based on cell cycle effective drugs. The possibility remains, at least for the moment, to stratify tumours according to their cellular heterogeneity. Different protocols could then be assigned to classes of tumours. Such an approach could be completed by further advances in the cellular monitoring of individual tumours.

Alkylating Agents↗
PubMed1986

[Studies of the cell kinetics of human malignant testicular tumors].

The cellular DNA-content of 75 malignant testicular germ-cell tumours was determined by flow cytometry. The results are: Aneuploidy is a certain tumour marker in 95% of germ-cell tumours. The DNA-indices range from 2 c (diploid) to 6 c with a modal value around 3 c. 23% of germ-cell tumours are multiclonal. The S-phase percentage is higher than those of the most other solid tumours investigated so far and is 25.5% in seminomas and 35% in non-seminomatous germ-cell tumours. Further investigations of a greater number of tissues will show the importance of DNA-contents measurement by flow cytometry for the prognosis of testicular tumours, representing an addition to histopathology.

Aneuploidy↗