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Biomedical subjects

A Kuhn

Publications and source records attributed to A Kuhn.

At least 181 records · Page 10Linked to original sources
PubMed1985

[Malignant transformation of cutaneous cylindromas. 2 case reports and a review of the literature].

We report on two female patients (age 78 and 81) suffering from multiple hereditary cylindromas which had grown, changed in color towards a bluish note, and partly exulcerated. The lesions were widely excised; plastic surgical reconstruction resulted in satisfactory healing. Histological examination showed similar features in both patients: We observed decreased differentiation of structures otherwise typical for cylindromas, polymorphism of cells and nuclei, mitoses, and beginning infiltration of the galea. Although there were no metastases found, malignant transformation was deduced from sudden growth, exulceration, as well as dedifferentiation of histological structures in combination with infiltrative expansion.

Aged↗
PubMed1984

The discrimination between Rb+ and K+ by Escherichia coli is changed after bacteriophage T7 infection.

Rb+ and K+ have similar chemical properties. They share the uptake systems in Escherichia coli and can replace each other inside the cell. These common features led to experiments in which the radioactive isotope 86Rb was used to trace intracellular K+ fluxes. However, the E. coli pumps discriminate between these two ions and one should thus be cautious using 86Rb+ as a tracer for K+. We now report that T7 infection alters the degree of discrimination in such a way that changes of intracellular Rb+ do not reflect changes of K+. It has been observed that shortly after infection the 86Rb+ level was strongly reduced (Ponta, H., Altendorf, K.-H. and Schweiger, M. (1976) Mol. Gen. Genet. 149, 145-150). In contrast, determination of the K+ content showed no change directly after infection (Kuhn, A., Jütte, H. and Kellenberger, E. (1983) J. Virol. 47, 540-552). The efflux of 86Rb was only evident when Rb+ was used in trace amounts. In media conditions under which intracellular K+ was mainly replaced by Rb+, 86Rb+ efflux was not observed.

Biological Transport, Active↗
PubMed1984

Isolation of the prohead core of bacteriophage T4 after cross-linking and determination of protein composition.

The naked core of bacteriophage T4 was isolated ex vivo after cross-linking with either glutaraldehyde or dithiobis(succinimidyl propionate). The isolated particles appeared to be morphologically identical to the cores found in thin sections, to those demonstrated in in situ lysis preparations, and to core structures assembled in vitro. Treatment with glutaraldehyde provided core particles which were morphologically well preserved, whereas dithiobis(succinimidyl propionate)-induced cross-linking was reversible and allowed analysis of the protein composition of the isolated particles. The identity of the reversibly cross-linked particles with those obtained after irreversible cross-linking was suggested by their morphology and their similar sedimentation behavior. Immunolabeling confirmed the structural presence of the main core protein in both structures. Gel electrophoresis of reversibly cross-linked cores revealed the essential head proteins gp22, gp67, and gp21, the three internal proteins IPI, IPII, and IPIII, and a 17K protein.

Antibodies, Viral↗
PubMed1983

Purification and characterization of a bifunctional L-(+)-tartrate dehydrogenase-D-(+)-malate dehydrogenase (decarboxylating) from Rhodopseudomonas sphaeroides Y.

A bifunctional enzyme, L-(+)-tartrate dehydrogenase-D-(+)-malate dehydrogenase (decarboxylating) (EC 1.1.1.93 and EC 1.1.1. . . , respectively), was discovered in cells of Rhodopseudomonas sphaeroides Y, which accounts for the ability of this organism to grow on L-(+)-malate. The enzyme was purified 110-fold to homogeneity with a yield of 51%. During the course of purification, including ion-exchange chromatography and preparative gel electrophoresis, both enzyme activities appeared to be in association. The ratio of their activities remained almost constant [1:10, L-(+)-tartrate dehydrogenase/D-(+)-malate dehydrogenase (decarboxylating)] throughout all steps of purification. Analysis by polyacrylamide gel electrophoresis revealed the presence of a single protein band, the position of which was coincident with both L-(+)-tartrate dehydrogenase and D-(+)-malate dehydrogenase (decarboxylating) activities. The apparent molecular weight of the enzyme was determined to be 158,000 by gel filtration and 162,000 by ultracentrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielded a single polypeptide chain with an estimated molecular weight of 38,500, indicating that the enzyme consisted of four subunits of identical size. The isoelectric point of the enzyme was between pH 5.0 and 5.2. The enzyme catalyzed the NAD-linked oxidation of L-(+)-tartrate as well as the oxidative decarboxylation of D-(+)-malate. For both reactions, the optimal pH was in a range from 8.4 to 9.0. The activation energy of the reaction (delta Ho) was 71.8 kJ/mol for L-(+)-tartrate and 54.6 kJ/mol for D-(+)-malate. NAD was required as a cosubstrate, and optimal activity depended on the presence of both Mn2+ and NH4+ ions. The reactions followed Michaelis-Menten kinetics, and the apparent Km values of the individual reactants were determined to be: L-(+)-tartrate, 2.3 X 10(-3) M; NAD, 2.8 X 10(-4) M; and Mn2+, 1.6 X 10(-5) M with respect to L-(+)-tartrate; and D-(+)-malate, 1.7 X 10(-4) M; NAD, 1.3 X 10(-4); and Mn2+, 1.6 X 10(-5) M with respect to D-(+)-malate. Of a variety of compounds tested, only meso-tartrate, oxaloacetate, and dihydroxyfumarate were effective inhibitors. meso-Tartrate and oxaloacetate caused competitive inhibition, whereas dihydroxyfumarate caused noncompetitive inhibition. The Ki values determined for the inhibitors were, in the above sequence, 1.0, 0.014, and 0.06 mM with respect to L-(+)-tartrate and 0.28, 0.012, and 0.027 mM with respect to D-(+)-malate.

Alcohol Oxidoreductases↗
PubMed1981

Substrate specificity of citrate lyase deacetylase of Rhodopseudomonas gelatinosa and Rhodopseudomonas palustris.

Citrate lyase (EC 4.1.3.6) isolated from Rhodopseudomonas palustris was investigated with regard to its kinetic properties and its subunit composition. This enzyme was inactivated by citrate lyase deacetylase (EC 3.1.2.-) of Rhodopseudomonas gelatinosa. A corresponding cross-reaction was measured with partially purified deacetylase of R. palustris and citrate lyase of R. gelatinosa. The three different subunit types (alpha, beta, and gamma) of citrate lyase from R. gelatinosa wee purified to homogeneity, and antibodies were prepared against each of the three subunits and against the native enzyme complex. In corresondence with the enzymatic interactions, immunological cross-reactions were found between anti-enzyme and anti-large subunit antibodies and citrate lyase from R. palustris. On the other hand, no immunological cross-reactions were detectable among each of the antibodies and citrate lyases from Enterobacter aerogenes, Streptococcus diacetilactis, and Clostridium sphenoides. Antibodies against the large subunit of citrate lyase inhibited the deacetylase, but antibodies against the middle and small subunits did not, indicating that the large subunits of citrate lyase are involved in binding the deacetylase.

Antibodies, Bacterial↗
PubMed1980

Different sensitivities of prostaglandin-cyclooxygenases in blood platelets and coronary arteries against non-steroidal antiinflammatory drugs.

The action of the non-steroidal antiinflammatory drugs indomethacin, tiaprofenic acid, diclofenac and meclofenamate on vascular and platelet-cyclooxygenases was studied by measuring the arachidonic acid-induced thromboxane A2 (TXA2)-formation of washed human platelets and prostacyclin (PGI2)-formation of bovine coronary artery rings. TXA2 was bioassayed as RCS on rabbit aorta strips, PGI2 in terms of its antiaggregatory activity on ADP-induced aggregation of human platelet-rich plasma. All of the substances studied produced concentration-dependent inhibition of PGI2- and RCS-release. The IC50 [micrometer] in inhibition of RCS-formation was 0.019 for indomethacin, 0.070 for tiaprofenic acid but 44.9 for meclofenamate and 63.2 for diclofenac. The IC50 [micrometer] in inhibition of PGI2-release was 0.42 for diclofenac, 0.63 for indomethacin and 0.99 for tiaprofenic acid. The data suggest (1) high sensitivity of human platelet-cyclooxygenase against indomethacin and tiaprofenic acid, (2) different sequence of the substances studied in inhibiting arachidonic acid-induced TXA2- and PGI2-formation. The possible therapeutic value of selective inhibition of platelets and vascular cyclooxygenases is discussed.

Animals↗
PubMed1980

Citrate lyase deacetylase of Rhodopseudomonas gelatinosa. Isolation of the enzyme and studies on the inhibition by L-glutamate.

Citrate lyase deacetylase or acetyl-S-(acyl-carrier protein) enzyme thioester hydrolase (acetate) (EC 3.1.2-), was purified 3100-fold with a yield of 3.8% from cell extracts of Rhodopseudomonas gelatinosa. The final enzyme preparation gave a single protein band upon polyacrylamide-gel electrophoresis in the absence or in the presence of sodium dodecylsulfate. The molecular weight of the native enzyme was estimated by gel filtration to be 14 300 +/- 1000. Sodium dodecylsulfate/polyacrylamide gel electrophoresis yielded a molecular weight of 7300 +/- 600 indicating that the enzyme consisted of two subunits. Citrate lyase deacetylase acted as an S-acetyl enzyme thioesterhydrolase because it catalyzed the conversion of citrate lyase (S-acetyl form) into citrate lyase (sulfhydryl form) and acetate. Citrate lyase deacetylase was strongly inhibited by L-glutamate. The half-maximal inhibitor concentration was 7.5 X 10(-4) M. and a Ki-value of 1.2 X 10(-4) M was determined. The mode of inhibition appeared to be of the linear mixed type. L-Glutamate was bound by citrate lyase deacetylase but not by citrate lyase. The pool concentrations of L-glutamate in R. gelatinosa were 10 mM when citrate was present in substrate amounts and 2.7 mM after total consumption of citrate. Simulation of conditions in vivo using homogeneous enzyme preparations of citrate lyase and citrate lyase deacetylase, and glutamate concentrations of 10 mM and 2.7 mM respectively, revealed that the rate of citrate lyase inactivation increased from 8% within 15 min during growth on citrate to 50% within 15 min in the absence of citrate.

Glutamates↗
PubMed1980

The action of non-steroidal antiinflammatory agents on platelet aggregation and vessel tone in relation to inhibition of PGI2- and thromboxane-release. With particular reference to 5-benzoyl-alpha-methyl-2-thiophene acetic acid (tiaprofenic acid).

The actions of 5-benzoyl-alpha-methyl-2-thiophene acetic acid (tiaprofenic acid) on platelet aggregation, coronary vascular tone and myocardial oxygen consumption were studied in vitro and compared to those of diclofenac sodium, indometacin and meclofenamate. Tiaprofenic acid dose-dependently and reversibly inhibited collagen- and arachidonic acid-induced aggregation of rabbit platelet-rich plasma (IC50 2--5 micromol/l) and was as effective in this system as the reference compounds. Tiaprofenic acid did not alter the myocardial oxygen consumption up to 120 micromol/l but produced reversible and dose-dependent increases in the coronary vascular tone of both guinea pig hearts and isolated bovine coronary arteries at 0.1--10 micromol/l concentrations. This coronary vasomotor activity of tiaprofenic acid could be correlated to its ability to inhibit the vascular PGI2 production whereas the inhibition of platelet aggregation by all of the substances studied does not seem to be tightly correlated to their inhibitory effect on the thromboxane formation of blood platelets.

Animals↗