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Biomedical subjects

J Koch

Publications and source records attributed to J Koch.

At least 163 records · Page 9Linked to original sources
PubMed1993

A novel variety of atypical Pneumocystis carinii infection after long-term prophylactic pentamidine inhalation in an AIDS patient: large lower lobe pneumocystoma.

Atypical pulmonary manifestations of Pneumocystis carinii infection and fair numbers of extrapulmonary and disseminated infections have lately been documented in patients with human immunodeficiency virus infection treated prophylactically with inhalative pentamidine. We report the case of a 32-year-old homosexual patient who was assessed for complaints of night sweats, weight loss, and progressive malaise. The patient denied any respiratory tract symptoms such as cough, sputum production, pleuritic chest pain, or shortness of breath. Chest X-ray revealed two large round noncavitating lesions in the lower lobe of the right lung. Pneumocystomas were diagnosed by fine-needle aspiration. A 3-week course of intravenous high-dose cotrimoxazole resulted in amelioration of symptoms but no change in the radiographic appearance of the pulmonary lesions. Four months later the patient is alive and stable and is being treated with pentamidine inhalation of 300 mg per 2 weeks and two tablets of pyrimethamine sulfadoxine per week.

AIDS-Related Opportunistic Infections↗
PubMed1993

Two N5,N10-methylenetetrahydromethanopterin dehydrogenases in the extreme thermophile Methanopyrus kandleri: characterization of the coenzyme F420-dependent enzyme.

It was recently reported that the extreme thermophile Methanopyrus kandleri contains only a H2-forming N5,N10-methylenetetrahydromethanopterin dehydrogenase which uses protons as electron acceptor. We describe here the presence in this Archaeon of a second N5,N10-methylenetetrahydromethanopterin dehydrogenase which is coenzyme F420-dependent. This enzyme was purified and characterized. The enzyme was colourless, had an apparent molecular mass of 300 kDa, an isoelectric point of 3.7 +/- 0.2 and was composed of only one type of subunit of apparent molecular mass of 36 kDa. The enzyme activity increased to an optimum with increasing salt concentrations. Optimal salt concentrations were e.g. 2 M (NH4)2SO4, 2 M Na2HPO4, 1.5 M K2HPO4, and 2 M NaCl. In the absence of salts the enzyme exhibited almost no activity. The salts affected mainly the Vmax rather than the Km of the enzyme. The catalytic mechanism of the dehydrogenase was determined to be of the ternary complex type, in agreement with the finding that the enzyme lacked a chromophoric prosthetic group. In the presence of 1 M (NH4)2SO4 the Vmax was 4000 U/mg (kcat = 2400 s-1) and the Km for N5,N10-methylenetetrahydromethanopterin and for coenzyme F420 were 80 microM and 20 microM, respectively. The enzyme was relatively heat-stable and lost no activity when incubated anaerobically in 50 mM K2HPO4 at 90 degrees C for one hour. The N-terminal amino acid sequence was found to be similar to that of the F420-dependent N5,N10-methylenetetrahydromethanopterin dehydrogenase from Methanobacterium thermoautotrophicum, Methanosarcina barkeri, and Archaeoglobus fulgidus.

Amino Acid Sequence↗
PubMed1993

Purification of glutaryl-CoA dehydrogenase from Pseudomonas sp., an enzyme involved in the anaerobic degradation of benzoate.

Cell-free extracts of Pseudomonas sp. strains KB 740 and K 172 both contained high levels of glutaryl-CoA dehydrogenase when grown anaerobically on benzoate or other aromatic compounds and with nitrate as electron acceptor. These aromatic compounds have in common benzoyl-CoA as the central aromatic intermediate of anaerobic metabolism. The enzymatic activity was almost absent in cells grown aerobically on benzoate regardless whether nitrate was present. Glutaryl-CoA dehydrogenase activity was also detected in cell-free extracts of Rhodopseudomonas, Rhodomicrobium and Rhodocyclus after phototrophic growth on benzoate. Parallel to the induction of glutaryl-CoA dehydrogenase as measured with ferricenium ion as electron acceptor, an about equally high glutaconyl-CoA decarboxylase activity was detected in cell-free extracts. The latter activity was measured with the NAD-dependent assay, as described for the biotin-containing sodium ion pump glutaconyl-CoA decarboxylase from glutamate fermenting bacteria. Glutaryl-CoA dehydrogenase was purified to homogeneity from both Pseudomonas strains. The enzymes catalyse the decarboxylation of glutaconyl-CoA at about the same rate as the oxidative decarboxylation of glutaryl-CoA. The green enzymes are homotetramers (m = 170 kDa) and contain 1 mol FAD per subunit. No inhibition was observed with avidin indicating the absence of biotin. The N-terminal sequences of the enzymes from both strains are similar (65%).

Amino Acid Sequence↗
PubMed1993

Protective effect of verapamil on shock wave induced renal tubular dysfunction.

In a prospective randomized study, the effects of the calcium entry blocker verapamil on shock wave induced tubular impairment were examined. A total of 24 patients with renal pelvis or caliceal stones undergoing anesthesia-free extracorporeal shock wave lithotripsy (ESWL*) without auxiliary measures was randomly assigned to the verapamil group (12) or the control group (12). Four doses of verapamil (80 mg. each) were given orally starting the night before ESWL. Controls received no medication. To assess renal tubular function the urinary excretion of alpha 1-microglobulin, N-acetyl-beta-glucosaminidase and Tamm-Horsfall protein were determined before, immediately, and 12 and 24 hours after ESWL. After ESWL there was an increase in urinary alpha 1-microglobulin and N-acetyl-beta-glucosaminidase, which was significantly higher in the control than in the verapamil group. Tamm-Horsfall protein, a glycoprotein synthesized by the distal tubules, decreased significantly less in the verapamil group compared to the controls. Our results indicate that verapamil exhibits a protective effect on shock wave induced tubular damage. The underlying mechanisms are not elucidated yet, and direct actions on tubular cells and interference with renal hemodynamics are to be discussed.

Acetylglucosaminidase↗
PubMed1993

Endosonography for preoperative locoregional staging of esophageal and gastric cancer.

To assess the accuracy and limitations of endoscopic ultrasonography (EUS) in the preoperative staging of esophageal and gastric carcinoma, we performed a prospective controlled study over a five year period. Data from 63 patients with esophageal cancer and 147 patients with gastric cancer who underwent surgery were available for comparison of the endosonographic TNM classification to the histophathological findings of the resected specimens. The overall accuracy of EUS in the assessment of tumor infiltration depth was 85.7% and 78% in esophageal and gastric cancer, respectively. The sensitivity of EUS in the detection of regional lymph node metastases was 90% in esophageal and 87% in gastric carcinoma. The most frequent causes of misdiagnoses by endosonography were microscopic tumor invasion and peritumorous inflammatory changes. The inability to traverse a tumor stenosis restricted the endosonographic evaluation in 31.6 and 14% of the cases with esophageal and gastric cancer, respectively.

Endoscopy, Gastrointestinal↗
PubMed1993

Identification of a supernumerary der(18) chromosome by a rational strategy for the cytogenetic typing of small marker chromosomes with chromosome-specific DNA probes.

A case of a supernumerary der(18) marker chromosome is presented. The chromosomal origin of the marker chromosome was not evident by traditional chromosome analysis, but was determined by PRimed IN Situ labelling (PRINS) with chromosome specific centromere probes as primers for chain elongation in situ. For this purpose a strategy was developed which, in a few simple reactions, makes it possible unequivocally to determine the origin of any small marker chromosome. The approach does not require any hints about the origin of the chromosome prior to the analysis, since the chromosomal origin of the marker is established through PRINS reactions with pooled and single chromosome-specific centromere probes. Identification, mosaic screening and structural analysis require a total of 8-9 such reactions and may, due to the extreme speed of the PRINS reaction, be obtained within a single working day.

Chromosome Aberrations↗
PubMed1993

Applicability of the critical difference.

The present study is concerned with the critical difference, which may help to judge whether or not the difference between two consecutive measurements with a certain probability (i.e. 95 percent) may be ascribed to natural variation. Knowledge of the applicability of the critical difference in veterinary medicine is sparse and therefore, to justify future use of the critical difference, it is important to know whether or not the critical difference performs as expected. The hypothesis to be tested in this study was that at least 95 percent of the differences between consecutive measurements, that have been obtained in animals where the component measured is known to be unchanged, should be within the critical difference. From previous studies it was known that a low-sodium diet had no influence on the plasma potassium concentration. The critical difference of the plasma potassium concentration in dogs was calculated as 0.5 mmol/l. using weekly measurements of this plasma component in a group of twenty healthy dogs. To test the hypothesis, this value was compared to the differences between consecutive weekly measurements of this plasma component in another group of eight dogs fed a low-sodium diet for five weeks. In agreement with previous studies, the plasma potassium concentration in the eight dogs did not change significantly during the feeding experiment. Of the fourty differences between consecutive weekly measurements, thirty-six were within the critical difference. This number was not different from the number expected from the hypothesis and thus, the critical difference performed as expected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1993

Repeated primed in situ labeling: formation and labeling of specific DNA sequences in chromosomes and nuclei.

A new version of our previously published PRINS (PRimed IN Situ labeling) method is presented. It represents a significant improvement in the detection of specific DNA sequences in situ. The idea is to perform the reaction repeatedly, rather than just once. This change of strategy results in a localized accumulation of sequence-specific labeled DNA, resulting in up to a 15-fold amplification of the signal as compared to the standard PRINS method. Interestingly, the retention of the labeled DNA is so good that it stays within the chromosomal band where it is synthesized, provided that the reaction is not performed an excessive number of times. The key trick is the performance of the procedure on small glass slides in PCR tubes, thereby avoiding the use of cover slips. In addition, use of the small glass slides seems to give less variance when the signals are quantified in a fluorescence microscope.

Base Sequence↗
PubMed1993

[Results of goniotrepanation in chronic simple glaucoma after drug therapy and argon laser trabeculoplasty].

In a retrospective study the effects of goniotrephination following antiglaucoma medication and argon laser trabeculoplasty (ALT) were examined. The study addressed the first treated eye in each of 61 patients. In all patients tropial antiglaucoma medication was continued after ALT. In the period between ALT and goniotrepanation the cup-disc ratio (CDR) progressed significantly (P < 0.01), with worsening of visual field defects. The long-term antiglaucoma medication and the ALT had no effect on the wound healing following the filtering procedure. ALT is contraindicated in preexisting pathologic CDR and visual field defects. In such cases intraocular pressure must be reduced to below 20 mmHg: filtration surgery is effective in lowering the intraocular pressure sufficiently.

Adrenergic beta-Antagonists↗
PubMed1993

Improvement of the predictive value of CD4+ lymphocyte count by beta 2-microglobulin, immunoglobulin A and erythrocyte sedimentation rate. The Multicentre Cohort Study Group.

OBJECTIVE: To evaluate whether the use of immunological markers in addition to CD4+ lymphocyte count can improve the prediction of the probability of developing AIDS within a given period. DESIGN AND SETTING: Prospective multicentre cohort study of homosexual men. PATIENTS: A total of 447 HIV-positive homosexual men followed prospectively at 6-month intervals (median time of observation, 47 months). METHODS: Estimation of AIDS-free time using lifetable plots by Cutler and Ederer and Weibull parametric models. A stepwise multivariate regression analysis was used to calculate the optimal combination of the parameters studied. RESULTS: In general CD4+ lymphocyte counts are most important for the prediction of AIDS-free time. The use of serum levels of beta 2-microglobulin (beta 2M), immunoglobulin A (IgA) and erythrocyte sedimentation rate (ESR) can significantly improve the predictive value of CD4+ lymphocyte counts. However, the usefulness of these parameters depends on the stage of HIV disease. In patients with a CD4+ lymphocyte count > 500 x 10(6)/l, only IgA level had a significant predictive value; none of the other parameters significantly improved the model. In patients with a CD4+ lymphocyte count < 500 x 10(6)/l, the absolute number of CD4+ cells itself was the most important single predictive parameter, but the prediction of AIDS was significantly improved by the addition of the other parameters investigated. The most powerful combination of parameters in this group was CD4+ count, beta 2M and ESR. CONCLUSION: Determination of serum IgA, beta 2M and ESR in addition to CD4+ lymphocyte count may aid the choice of specific therapeutic regimens or systems of care for HIV-positive individuals.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Adverse events temporally associated with immunizing agents.

In Canada during 1990, a total of 2832 reports of adverse events temporally associated with the administration of immunizing agents were received by the Childhood Immunization Division of the Laboratory Centre for Disease Control. This paper summarizes the data collected, describes the surveillance system, and demonstrates that, with more than 12,000,000 doses of vaccines distributed during 1990, the incidence of adverse events reported is very low.

Adverse Drug Reaction Reporting Systems↗
PubMed1993

[Phacoemulsification without suture. Results of implantation of a large optic PMMA lens].

Sutureless phacoemulsification with implantation of a 7-mm PMMA intraocular lens was performed through a modified scleral tunnel in 100 consecutive patients. This was done to minimize postoperative astigmatism while retaining the advantages of implanting intraocular lenses with large optics. Visual and keratometric results and complications are reported after completion of a follow-up period of 6 months for the first 30 patients. Average uncorrected visual acuity improved from 0.13 preoperatively to 0.30 as early as 1 week postoperatively. Average best-corrected visual acuity improved from 0.23 before surgery to 0.51 as early as 1 week after surgery. No significant changes in visual acuity were recorded thereafter. The absolute value of keratometric astigmatism was not increased significantly at any postoperative examination time. The induced cylinder (Jaffe and Clayman) shifted from -1.27 D x 166 degrees at 1 week to 1.18 D x 91 degrees at 1 month postoperatively without further relevant changes thereafter. Endothelial cell loss did not differ from that reported by other authors after conventional cataract surgery. Corneal thickness was not increased significantly at any postoperative examination time. Implantation of intraocular lenses with large optics through a scleral tunnel allows quick visual rehabilitation as well as early stability of refraction.

Adult↗
PubMed1992

Elucidation of the sequence-specific third-strand recognition of four Watson-Crick base pairs in a pyrimidine triple-helix motif: T.AT, C.GC, T.CG, and G.TA.

We report a specific pattern of recognition by third-strand bases for each of the four Watson-Crick base pairs within a pyrimidine triple-helix motif as determined by PAGE: T.AT, C.GC, T.CG, and G.TA. Our recognition scheme for base triplets is in agreement with previous studies. In addition, we identified another triplet, T.CG, under physiological conditions, in which formation of triple helix was observed at equimolar ratios of the third strand and duplex target. Although different nearest-neighbor effects are expected, this finding extends the base-recognition code to all 4 base pairs in double-stranded DNA under physiological conditions. Base-composition analysis of putative triplex species provided independent evidence for the formation of triplex and confirmed the base-recognition code determined by PAGE. Moreover, the formation of triplex, as detected by gel electrophoresis, was seen to be an all-or-none phenomenon, dependent upon a single-base mismatch among 21 nucleotides. This result suggests a high specificity for the recognition of double-stranded DNA by a third strand. In addition, we report the surprising finding that triplex stability depends on the length and sequence of the target duplex DNA.

Base Composition↗
PubMed1992

Enzymatic reduction of benzoyl-CoA to alicyclic compounds, a key reaction in anaerobic aromatic metabolism.

Different anaerobic bacteria can oxidize a variety of aromatic compounds completely to CO2 via one common aromatic intermediate, benzoyl-CoA. It has been postulated that anaerobically the aromatic nucleus of benzoyl-CoA becomes reduced. An oxygen-sensitive enzyme system is described catalyzing the reduction of benzoyl-CoA to trans-2-hydroxycyclohexanecarboxyl-CoA in a denitrifying Pseudomonas species grown anaerobically on benzoate plus nitrate. The assay mixture consists of cell extract, [U-14C]benzoyl-CoA, a [U-14C]benzoyl-CoA-generating system (consisting of [U-14C]benzoate, purified benzoate-CoA ligase, Mg(2+)-ATP, coenzyme A), an ATP-regenerating system (consisting of phosphoenolpyruvate, pyruvate kinase, myokinase), and a low-potential reductant [titanium(III) citrate]. The optimal pH is about 7, the specific activity 10 nmol benzoyl-CoA reduced min-1 x mg-1 protein. The apparent Km for benzoyl-CoA is below 50 microM. Five major products were found. One product is cyclohex-1-enecarboxyl-CoA which must have been formed by a benzoyl-CoA reductase. The other product is probably trans-2-hydroxycyclohexanecarboxyl-CoA rather than the cis-stereoisomer; this product must have been formed by a cyclohex-1-enecarboxyl-CoA hydratase. Two other products are likely to be intermediates of benzoyl-CoA reduction to cyclohex-1-enecarboxyl-CoA, suggesting that the reduction reaction is more complex. An early formed fifth product is more polar than cyclohexanecarboxyl- or cyclohex-1-enecarboxyl-CoA. The enzyme system is under oxygen control since it was not found in cells grown aerobically on benzoate. It is induced by aromatic compounds since its activity is low in cells grown anaerobically on acetate. The actual inducer is probably benzoyl-CoA rather than benzoate. This conclusion is drawn from the fact that the system is also present in cells grown anaerobically on phenol, phenylacetate, 4-hydroxybenzoate, or 2-aminobenzoate; the anaerobic metabolism of these compounds has been shown in this organism to proceed directly via benzoyl-CoA rather than via free benzoate.

Acetobacteraceae↗
PubMed1992

Isolation and characterization of polyferredoxin from Methanobacterium thermoautotrophicum. The mvhB gene product of the methylviologen-reducing hydrogenase operon.

The methylviologen-reducing hydrogenase operon of Methanobacterium thermoautotrophicum contains an open reading frame, mvhB, the product of which was predicted to have a molecular weight of 44 kDa and to contain as many as 48 iron atoms in 12 [4Fe-4S] clusters, and was therefore suggested to be a polyferredoxin. We have now, for the first time, isolated this polyferredoxin. Its identity with the mvhB gene product was evidenced by a comparison of the N-terminal amino acid sequence. The dark-brown protein of apparent molecular weight 44 kDa was found to contain 53 mol Fe and 43 mol acid-labile sulfur per mol. The UV/visible spectrum showed two maxima at 280 nm and 390 nm, and a shoulder at 308 nm. The A390/A280 ratio was 0.73. The molar extinction coefficient at 390 nm was 170,000 M-1.cm-1. In the dithionite reduced state the protein displayed an EPR spectrum like that of [4Fe-4S] clusters. The results indicate that the mvhB gene product is indeed a polyferredoxin.

Amino Acid Sequence↗