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T Zimmer

Publications and source records attributed to T Zimmer.

At least 37 records · Page 2Linked to original sources
PubMed1998

Relation between evolutionary distance and enzymatic properties among the members of the CYP52A subfamily of Candida maltosa.

The CYP52A subfamily of the alkane-assimilating yeast Candida maltosa consists of six structurally related isoforms. Four of them (CYP52A3, 4, 5, and 9) are strongly induced by alkanes and play an important role for the conversion of various alkanes and fatty acids. Taking advantage of a homologous overexpression system, we found in the present study that both of the two other CYP52A forms, CYP52A10 and CYP52A11, represent specialists for the hydroxylation of lauric acid suggesting their preference for short-chain fatty acids. At the same time, they hydroxylated palmitic acid only moderately and failed to convert hexadecane. Based on the now completed knowledge about the principal substrate specificities of all members of the CYP52A subfamily of C. maltosa, it became apparent that evolutionarily more distantly related P450 forms developed either to alkane or to fatty acid hydroxylases, whereas P450 forms which retained the ability to convert both types of substrates were also found to be evolutionarily related to both alkane and fatty acid hydroxylases.

Candida↗
PubMed1998

Mutual conversion of fatty-acid substrate specificity by a single amino-acid exchange at position 527 in P-450Cm2 and P-450Alk3A.

The two eukaryotic fatty-acid hydroxylases P-450Cm2 and P-450Alk3A, which represent CYP52A4 variants naturally occurring in the yeast Candida maltosa, were characterized with respect to their substrate specificity. Whereas P-450Cm2 was found to catalyse lauric acid omega-hydroxylation with greater efficiency, P-450Alk3A had higher palmitic acid turnover numbers compared to P-450Cm2, resulting in ratios of lauric acid to palmitic acid turnover rates of nearly 11 and 3 for P-450Cm2 and P-450Alk3A, respectively. As shown by means of chimeric enzymes and site-directed mutagenesis, the key residue determining these differences in substrate specificity was found to be a single amino acid at position 527. Interestingly, the mutual exchange of valine (P-450Cm2) and leucine (P-450Alk3A) led to a direct transposition of specificity, suggesting that amino acids at this site may determine the efficiency of fatty-acid hydroxylation relatively independently of other active-site residues. This was further supported by the finding that P-450Cm2 and P-450Alk3A with methionine at position 527 displayed almost identical hydroxylation activities. Moreover, methionine to leucine substitutions at the corresponding alignment position in P-450Cm1 (CYP52A3), P-450Alk2A (CYP52A5) and P-450Alk5A (CYP52A9) altered the fatty-acid specificity of these enzymes. In comparison to the structure of the bacterial P-450BM3 (CYP102), we propose that the amino acid at position 527 may serve to close the substrate-binding pocket near to the haem in the fatty-acid-omega-hydroxylating P-450 of the CYP52 family.

Amino Acid Sequence↗
PubMed1998

Isozyme function of n-alkane-inducible cytochromes P450 in Candida maltosa revealed by sequential gene disruption.

An n-alkane-assimilating yeast Candida maltosa contains multiple n-alkane-inducible forms of cytochromes P450 (P450alk), which can be assumed to catalyze terminal hydroxylation of n-alkanes in the assimilation pathway. Eight structurally related P450alk genes have been identified. In the present study, the function of four major isoforms of P450alk (encoded by ALK1, ALK2, ALK3, and ALK5 genes) was investigated by sequential gene disruption. Auxotrophic markers used for the selection of disrupted strains were regenerated repeatedly through either mitotic recombination between heterozygous alleles of the diploid genome or directed deletion of the marker gene, to allow sequential gene disruptions within a single strain. The strain depleted of all four isoforms could not utilize n-alkanes for growth, providing direct evidence that P450alk is essential for n-alkane assimilation. Growth properties of a series of intermediate disrupted strains, plasmid-based complementation, and enzyme assays after heterologous expression of single isoforms revealed (i) that each of the four individual isoforms is alone sufficient to allow growth on long chain n-alkane; (ii) that the ALK1-encoding isoform is the most versatile and efficient P450alk form, considering both its enzymatic activity and its ability to confer growth on n-alkanes of different chain length; and (iii) that the ALK5-encoding isoform exhibits a rather narrow substrate specificity and thus cannot support the utilization of short chain n-alkanes.

Alkanes↗
PubMed1998

Endoscopic sclerotherapy with fibrin glue as compared with polidocanol to prevent early esophageal variceal rebleeding.

BACKGROUND/AIMS: Endoscopic sclerotherapy is of proven benefit for patients after esophageal variceal bleeding, but is associated with substantial local and systemic complications. Since fibrin glue is a promising agent for endoscopic sclerotherapy of esophageal varices, we compared its safety and efficacy in patients after esophageal variceal bleeding. PATIENTS AND METHODS: In a randomized, controlled trial, 36 patients with an acute episode of variceal bleeding were endoscopically treated with either polidocanol (18 patients) or fibrin glue (18 patients) by intravariceal injections within 12 h of admission. Tissue compatibility, incidence of various complications, episodes of rebleeding and overall survival rates were investigated. RESULTS: Rebleeding, especially from enrollment to day 28, was less common in the fibrin group (p=0.046), and all patients treated with fibrin glue survived for more than 28 days, whereas five patients treated with polidocanol died within this period. The incidence of sclerotherapy-induced ulcers was significantly lower in the fibrin group than in the polidocanol group (p=0.001), and major complications such as perforation or ulcer bleeding were observed only in the polidocanol group. There were no complications in any group due to activation of systemic coagulation, fibrinolysis or clinically relevant pulmonary embolization. CONCLUSIONS: We conclude that fibrin glue is an efficient and safe agent for endoscopic sclerotherapy of bleeding esophageal varices, especially in the immediate posthemorrhagic period.

Aged↗
PubMed1998

[Value of magnetic resonance tomography in preoperative staging of stomach carcinoma].

The value of MRI as a preoperative staging procedure in stomach carcinomas compared to CT and endosonography was examined in a prospective study and correlated with the pathohistological results. MRI showed better correlation with the pathohistological evaluation at the T3, T4, N and M stage than the other two test procedures. MRI is thus a suitable staging procedure for stomach carcinomas.

Adult↗
PubMed1997

[Endoscopic ultrasound of pathological mediastinal findings].

INTRODUCTION: Mediastinal diseases are mostly diagnosed by CT and MRI. The applicability of ultrasound is limited by the surrounding air- and bone-containing thorax, which permits only restricted echo windows. Transesophageal endoscopic ultrasonography circumvents this problem and ensures visualization of parts of the mediastinum. PATIENTS AND METHODS: We report our results in 38 patients with pathological mediastinal findings who were examined by endoscopic ultrasound between 1988 and 1993. The diagnoses were established by imaging and/or histological procedures. RESULTS: The following mediastinal diseases were diagnosed in 38 patients: aberrant right subclavian artery (n = 3), right aortic arch (n = 1), aortic aneurysm (n = 6), cysts (n = 4), retrosternal struma (n = 3), mediastinal lymph node tuberculosis (n = 1), Hodgkin's/non-Hodgkin's lymphomas (n = 11), lymph node involvement in bronchogenic carcinoma (n = 8), mediastinal inflammatory fibrosarcoma (n = 1). Altogether, 37/38 pathological findings were demonstrated endosonographically. CONCLUSIONS: The results in this small group of patients with pathological mediastinal findings show that endoscopic ultrasound can give additional information to conventional imaging methods. A prospective comparative study is necessary to evaluate this procedure in comparison to the established imaging techniques.

Deglutition Disorders↗
PubMed1997

A 7-year-old child with primary tumour localisation in the distal duodenum--new imaging procedures for an improved diagnosis.

UNLABELLED: Duodenal gastrinomas in childhood are extremely rare and often missed at first medical consultation. We report on a 7-year-old child with sporadic gastrinoma of primary localisation in the distal duodenum. Small metastases in the liver and regional nodes were detected pre-operatively by somatostatin receptor scintigraphy (SRS) but not by other conventional imaging procedures. Diagnostic procedures include pre-operative SRS, endoscopic ultrasound and intra-operative endoscopic transillumination. CONCLUSION: Gastrinomas are rare abdominal tumours in childhood. Pre-operative tumour-specific diagnosis is possible by 111indium pentreotide SRS.

Biomarkers, Tumor↗
PubMed1997

[Value of endoscopic ultrasound examination of the mediastinum in Hodgkin's and non-Hodgkin's lymphomas].

AIM: The applicability of ultrasound for diagnosing mediastinal diseases is limited by the surrounding thorax containing air and bone, permitting only restricted echo windows. Transoesophageal endoscopic ultrasound circumvents this problem and provides good visualisation of nearly all parts of the mediastinum. We evaluated the value of endoscopic ultrasonography for mediastinal staging of Hodgkin's and non-Hodgkin lymphoma patients. PATIENTS AND METHODS: From August 1994 to July 1995 36 Hodgkin's and non-Hodgkin lymphoma patients underwent clinical staging and were endosonographically examined for mediastinal involvement. CT in the spiral technique was used as the reference. RESULTS: In assessing mediastinal involvement, endoscopic ultrasound revealed a sensitivity of 96% and a specificity of 75%. There were limitations in the right paratracheal region and the area lateral to the aortic arch. CONCLUSION: Endoscopic ultrasound is a highly valuable imaging procedure for diagnosing mediastinal spread of malignant lymphomas and has interesting potentials in assessing the clinical course during therapy.

Endosonography↗
PubMed1997

[MR cholangiopancreatography using an open low field system of 0.2 tesla: early clinical results compared with a high field system (1.5 tesla) and ERCP].

AIM: To evaluate MR cholangio-pancreatography (MRCP) using an open low magnetic field apparatus in normals and in patients with mechanical cholestasis. METHODS: MRCP was performed on five normals and on 30 patients, using both an 0.2 Tesla and 1.5 Tesla apparatus. With the low field system, rapid acquisition by relaxation enhancement was used, for the high field system, half Fourier acquisition single shot turbo spin-echo sequences were used. In all patients, sonography and ERCP or PTC was performed; 23 underwent surgery. RESULTS: In all normals it was possible to show the bile duct, hepatic duct, gall bladder and intrahepatic ducts of the first order. Using the high field system, second order ducts could be shown and sometimes third order ducts. In the patients, MRCP, using either system, demonstrated all 21 obstructive sites due to tumours or stenoses. Stones were shown in 69% by the low field system and in 88% by the high field system. CONCLUSION: MRCP can be successfully carried out using the low field system. In the presence of mechanical cholestasis, image quality is adequate for the localisation of stenoses and occlusions, and, using an open magnet, is suitable for planning further intervention.

Adult↗
PubMed1997

Protein quality--a determinant of the intracellular fate of membrane-bound cytochromes P450 in yeast.

To elucidate mechanisms determining the intracellular localization of cytochromes P450, authentic and mutant cytochromes P450 52A4 (P450Cm2) and P450 52A5 (P450Alk2A) were heterologously expressed in Saccharomyces cerevisiae and the ultrastructure of the respective transformants was investigated by means of immunoelectron microscopy. As a result, overproduction of both wild-type P450 forms resulted in a massive proliferation of tubular membrane structures distributed over the whole cytoplasm. In contrast, all mutant P450Cm2 and Alk2A forms tested were mainly localized within stacks of paired membranes which often occurred in close vicinity to the nucleus. As found by serial sectioning of a single cell, these stacked membranes bearing the mutant P450 actually represented plates of consecutive membranes arranged one upon the other. A tubular network of endoplasmic reticulum membranes as observed after expression of the wild-type proteins could not be detected. Generally, the kind of mutation introduced into the P450 forms did not influence the morphology of the induced membranes. Even single amino acid exchanges in the cytosolic domain caused the formation of membrane stacks. The common feature of all mutant P450 forms causing the formation of stacked membranes was, however, their lower protein stability after heterologous expression in the S. cerevisiae host cells, compared to the stability of the authentic cytochromes P450. Furthermore, the proliferated membranes containing the different P450 forms were characterized by means of subcellular fractionation experiments. Using this approach, clear differences in the distribution of spectrally active and inactive P450 molecules were found. The results obtained suggest the presence of an intracellular sorting mechanism based on the protein quality, which finally leads to the differences in the intracellular distribution of wild-type and mutant cytochromes P450.

Candida↗
PubMed1997

[Intramural pseudodiverticulosis of the esophagus].

Esophageal intramural pseudodiverticulosis is a rare benign condition with the cardinal symptom of dysphagia mostly due to inflammatory strictures. The disease frequently develops in connection with alcohol abuse and esophageal reflux, candidiasis or motility disorders. Characteristic is the radiological visualization of intramural saccular contrast accumulations. We report on five patients with esophageal pseudodiverticulosis endoscopically diagnosed at our hospital within a period of five years. Four of these patients underwent extensive investigations for additional esophageal conditions: Histological/cytological examinations, manometry, pH-metry and endoscopic ultrasonography. These four patients had a pathological reflux with marked esophagitis and inflammatory strictures. We achieved long-lasting therapeutic results with complete relief by bougienage and reflux therapy with additional candidiasis treatment in two and motility treatment in one patient each. The detailed discussion deals with the clinical aspects, characteristics, therapy and pathogenesis.

Aged↗
PubMed1997

[Is routine tumor after-care after gastrectomy sensible?].

Only 22.3% of patients with recurrence after potentially curative gastrectomy are discovered in asymptomatic stages. Their prognosis is not different from those with symptomatic recurrence. Routine follow-up after gastrectomy can be abandoned.

Aftercare↗
PubMed1996

The CYP52 multigene family of Candida maltosa encodes functionally diverse n-alkane-inducible cytochromes P450.

The n-alkane-assimilating yeast Candida maltosa contains several structurally related cytochromes P450 (P450) encoded by the CYP52 multigene family, which are inducible by various long-chain hydrocarbons and fatty acids and which are responsible for the initial hydroxylation steps in the metabolism of these substrates. In the present work, the four major n-alkane-inducible C. maltosa P450 forms; CYP52A3, CYP52A4, CYP52A5, and CYP52A9, were enzymatically characterized, taking advantage of heterologous P450/reductase coexpression in Saccharomyces cerevisiae. Testing various alkanes and fatty acids, distinct preferences of the individual P450 forms concerning substrate class and chain length were detected, thus providing new insight into the functional diversity of the C. maltosa CYP52 family. Moreover, the results obtained emphasize these structurally related enzymes as a powerful tool for future studies on P450 structure-function relationships.

Alkanes↗
PubMed1996

Characterization of the n-alkane and fatty acid hydroxylating cytochrome P450 forms 52A3 and 52A4.

Two enzymes, P450 52A3 (P450Cm1) and 52A4 (P450Cm2), the genes of which belong to the CYP52 multigene family occurring in the alkane-assimilating yeast Candida maltosa, have been characterized biochemically and compared in terms of their substrate specificities. For this purpose, both the p450 proteins and the corresponding C. maltosa NADPH-cytochrome P450 reductase were separately produced by expressing their cDNAs in Saccharomyces cerevisiae, purified, and reconstituted to active monooxygenase systems. Starting from microsomal fractions with a specific content of 0.75 nmol P450Cm1, 0.34 nmol P450Cm2, and 10.5 units reductase per milligram of protein, respectively, each individual recombinant protein was purified to homogeneity. P450 substrate difference spectra indicated strong type I spectral changes and high-affinity binding of n-hexadecane (Ks= 26 micron) and n-octadecane (Ks = 27 microM) to P450Cm1, whereas preferential binding to P450Cm2 was observed using lauric acid (Ks = 127 microM) and myristic acid (Ks = 134 microM) as substrates. These substrate selectivities were further substantiated by kinetic parameters, determined for n-alkane and fatty acid hydroxylation in a reconstituted system, which was composed of the purified components and phospholipid, as well as in microsomes obtained after coexpressing each of the P450 proteins with the reductase. The highest catalytic activities within the reconstituted system were measured for n-hexadecane hydroxylation to 1-hexadecanol by P450Cm1 (Vmax = 27 microM x min-1, Km = 54 microM) and oxidation of lauric acid to 16-hydroxylauric acid by P450Cm2 (Vmax = 30 microM x min-1, Km = 61 microM). We conclude that P450Cm1 and P450Cm2 exhibit overlapping but distinct substrate specificities due to different chain-length dependencies and preferences for either n-alkanes or fatty acids.

Alkanes↗
PubMed1996

Endoscopic ultrasonography and somatostatin receptor scintigraphy in the preoperative localisation of insulinomas and gastrinomas.

BACKGROUND: Endoscopic ultrasonography (EUS) and somatostatin receptor scintigraphy (SRS) can detect a high percentage of gastroenteropancreatic neuroendocrine tumours especially in the upper gastrointestinal tract. The ability of these procedures to localise primary tumour lesions and metastases of gastrinomas and insulinomas was evaluated in comparison with transabdominal ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI). PATIENTS AND METHODS: In a prospective trial, patients with gastrinomas (n = 10) and insulinomas (n = 10) diagnosed by clinical signs and laboratory tests were assessed by EUS, SRS, US, CT and MRI. RESULTS: In 10 patients with gastrinoma and 10 patients with insulinoma, a total of 14 separate primary tumour lesions were histologically confirmed for each of the tumour entities. The mean diameter was 2.1 cm for gastrinomas and 1.5 cm for insulinomas. All insulinomas and nine gastrinoma lesions were located in the pancreas. Three gastrinomas were found in the duodenal wall, one in a periduodenal lymph node, and one in the liver, For gastrinomas, sensitivities were 79% with EUS, 86% with SRS and 29% with CT, US, and MRI. For insulinomas, sensitivities were 93% with EUS, 14% with SRS, 21% with CT and 7% with US and MRI. CONCLUSIONS: EUS is of high value for localising primary lesions of both tumour entities. SRS is a very sensitive procedure for diagnosing of gastrinomas but not insulinomas. CT, US and MRI are primarily useful for visualising metastases.

Adolescent↗
PubMed1996

[Gastric hamartoma and thyroid gland carcinoma with follicular and neuroendocrine differentiation in Cowden syndrome].

A 40-year old male patient presented with a history of subtotal strumectomy, excision of multiple cutaneous lesions at the upper trunk and gastrointestinal polyposis of unknown origin. The patient was admitted for weight loss and intermittent diarrhea. Physical examination revealed craniomegaly, papillomatosis of the oral mucosa and epigastric tenderness. Endoscopically, multiple polyps were seen in the stomach, the duodenum, the terminal ileum, the distal colon and the rectum. Histologically, these lesions were classified as hamartomatous and hyperplastic polyps. In the punctate of the relapsed nodular goitre, neoplastic follicular cells were found. These findings led to the diagnosis of Cowden's disease. A complete thyroidectomy was performed. The histology verified a follicular thyroid carcinoma and showed a combined expression of thyroglobulin and of the neuroendocrine marker synaptophysin (appr. 50% of all tumor cells). Chromogranin A (a neuroendocrine tumor marker) was also elevated in the serum of the patient. Postoperatively, a radioiodine therapy was performed and the clinical condition of the patient has improved ever since. The presented case of Cowden's disease is the first male patient with thyroid carcinoma. Early consideration of Cowden's disease is substantial as multiple malignant neoplasms may occur in this disorder in increased incidence.

Adenocarcinoma, Follicular↗