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J Jäger

Publications and source records attributed to J Jäger.

At least 37 records · Page 2Linked to original sources
PubMed1994

Significant improvement to the catalytic properties of aspartate aminotransferase: role of hydrophobic and charged residues in the substrate binding pocket.

The substrate specificity of tyrosine aminotransferase (eTAT) from Escherichia coli has been tested by transferring the critically different residues Leu39, Glu141, and Arg293 into equivalent positions of aspartate aminotransferase (eAAT). These residues are not directly involved in the catalytic process. The single mutant eAAT V39L possesses greater values of kcat/KM not only for tyrosine but also for aspartate and glutamate. In contrast, the double mutant eAAT P141E,A293R and also the triple mutant eAAT V39L,P141E,A293R exhibit smaller changes of kcat/KM. The converse mutants of tyrosine aminotransferase, in which critical residues of eAAT (Val39) and of mitochondrial AAT (Ala39, Val37) were transferred into equivalent positions of eTAT, exhibited generally decreased values of kcat/KM for both dicarboxylic and aromatic substrates. On the basis of the known structures of eAAT and eAAT V39L as well as of a refined model of eTAT, these results indicate that the different substrate specificities of eAAT and eTAT are due to multiple side chain differences and minor rearrangements of the backbone. The generally improved catalytic efficiency of the mutant eAAT V39L appears to be due to an indirect effect, namely, the facilitated closure of the active site upon substrate binding.

Amino Acid Sequence↗
PubMed1994

Three-dimensional structure of a mutant E. coli aspartate aminotransferase with increased enzymic activity.

The aspartate and tyrosine aminotransferases from Escherichia coli have 43% sequence identity and nearly identical active sites. Both are equally good enzymes for dicarboxylate substrates, but the latter transaminates aromatic amino acids 1000 times faster. In an attempt to discover the critical residues for this differential substrate specificity, the aspartate aminotransferase mutant V39L has recently been prepared. It showed improved Kcat/Km values for aspartate, glutamate and tyrosine and the corresponding oxo acids, mainly due to two to ten times lower Km values. For example, the Km values of V39L (wild type) for Asp and Glu are 0.12 (1.0) and 0.85 (2.7) mM respectively. The mutant was co-crystallized with 30 mM maleate from both polyethylene glycol and ammonium sulfate. Both structures were solved and refined to R-factors of 0.22 and 0.20 at 2.85 and 2.5 A resolution respectively. They bear strong resemblance to the closed structure of the wild type enzyme complexed with maleate. The unexpected feature is that, for the first time, the closed form was produced in crystals grown from ammonium sulfate. It is concluded that the mutation has shifted the conformational equilibrium towards the closed form, which leads to generally reduced substrate Kms.

Aspartate Aminotransferases↗
PubMed1993

Mutant aspartate aminotransferase (K258H) without pyridoxal-5'-phosphate-binding lysine residue. Structural and catalytic properties.

If the pyridoxal-phosphate-binding lysine residue 258 of aspartate aminotransferase is exchanged for a histidine residue, the enzyme retains partial catalytic competence [Ziak, M., Jaussi, R., Gehring, H. and Christen, P. (1990) Eur. J. Biochem. 187, 329-333]. The three-dimensional structures of the mutant enzymes of both chicken mitochondria and Escherichia coli were determined at high resolution. The folding patterns of the polypeptide chains proved to be identical to those of the wild-type enzymes, small conformational differences being restricted to parts of the active site. If aspartate or glutamate was added to the pyridoxal form of the mutant enzyme [lambda max 392 nm and 330 nm (weak); negative CD at 420 nm, positive CD at 370 nm and 330 nm], the external aldimine (lambda max = 430 nm; negative CD at 360 nm and 430 nm) transiently accumulated. Upon addition of 2-oxoglutarate to the pyridoxamine form (lambda max 330 nm, positive CD), a putative ketamine intermediate could be detected; however, with oxalacetate, an equilibrium between external aldimine and the pyridoxal form, which was strongly in favour of the former, was established within seconds. The transamination cycle with glutamate and oxalacetate proceeds only three orders of magnitude more slowly than the overall reaction of the wild-type enzyme. The specific activity of the mutant enzyme is 0.1 U/mg at 25 degrees C and constant from pH 6.0 to 8.5. Reconstitution of the mutant apoenzyme with [4'-3H]pyridoxamine 5'-phosphate resulted in rapid release of 3H with a first-order rate constant kappa' = 5 x 10(-4) s-1 similar to that of the wild-type enzyme. Apparently, in aspartate aminotransferase, histidine can to some extent substitute for the active-site lysine residue. The imidazole ring of H258, however, seems too distant from C alpha and C4' to act efficiently as proton donor/acceptor in the aldimine-ketamine tautomerization, suggesting that the prototropic shift might be mediated by an intervening water molecule. Transmination of the internal to the external aldimine apparently can be replaced by de novo formation of the latter, and by its hydrolysis in the reverse direction.

Animals↗
PubMed1991

[Pearl oyster dust as the cause of exogenous allergic alveolitis].

Many different inhalative substances may cause allergic alveolitis (hypersensitivity pneumonitis). We report on a worker who developed lung fibrosis due to the sensitization to pearl oyster shell dust. High concentrations of IgG antibodies to proteins (conchagens) of the shell which appear to represent the relevant antigens were found in the patient's serum.

Aged↗
PubMed1989

Crystallization and preliminary X-ray studies of an aspartate aminotransferase mutant from Escherichia coli.

Mutant aspartate aminotransferase V39L (Val39 replaced by Leu) from Escherichia coli has been crystallized into a monoclinic cell from a polyethylene glycol solution (pH 7.5) by vapor diffusion. The space group and the unit cell dimensions have been determined using a precession camera, a CAD4 diffractometer and a Nicolet Xentronics area detector to be P2(1) with a = 86.8 A, b = 79.9 A, c = 89.4 A, beta = 118.74 degrees. The crystals diffract to better than 2.3 A and are suitable for X-ray structure analysis.

Aspartate Aminotransferases↗
PubMed1988

[The histomorphology of granulomatous lipid pneumonia due to dietary fat aspiration in achalasia of the esophagus (megaesophagus)].

In some cases of achalasia, lungs may show characteristic granulomatous pneumonia, following non-symptomatic spill-over and aspiration of fat. The lesion is characterised by fat-containing vacuoles, necrosis, granulocytes, macrophages, some of them with lipid content, epithelioid and giant cells and fibrosis rich in lymphocytes. The histological pattern is pathognomonic and represents an entity. These alterations may be mistaken for tuberculosis and be distinguished from mineral-oil pneumonia (paraffinoma). Affected lung regions may be colonised by nontuberculous (atypical) mycobacteria.

Adolescent↗
PubMed1987

Localization of glycine uptake and receptors in the cat retina.

Immunocytochemistry using a monoclonal antibody against glycine receptors revealed that these receptors in cat retina are confined to the inner plexiform layer (IPL). The outer half of that layer showed strong patchy labelling with some indication of two bands corresponding to the on- and off-sublamina. High-affinity uptake of [3H]glycine followed by autoradiography labelled amacrine cells, bipolar cells and the outer portion of the IPL. Silver grains in the IPL were patchily distributed. These results indicate in the cat retina a close match between presynaptic glycinergic elements labelled by high-affinity uptake and the postsynaptic receptor sites for glycine revealed by immunocytochemistry.

Animals↗
PubMed1987

[Experiences with bronchoalveolar lavage in disseminated and other lung diseases].

In 860 patients 980 bronchoalveolar lavages were performed. The repeated BAL allows conclusions of the effect of treatment and the prognosis of the disease. BAL is together with other clinical findings an important new method in pulmology. Its value in diagnosis of interstitial pulmonary diseases and other pulmonary diseases is described with special view to occupational expositions.

Alveolitis, Extrinsic Allergic↗
PubMed1986

[Value of bronchoalveolar lavage for the diagnosis of adenocarcinoma of the lung].

The differentiation of interstitial lung diseases and disseminated lung tumors only by radiological methods is impossible. Cytological or histological examinations of specimens taken by bronchological or surgical examinations are able to confirm the diagnosis. In two cases of a disseminated process in which other bronchological diagnostic methods failed we found cells of an adenocarcinoma by BAL. We recommend this method for differential diagnostic between interstitial lung diseases and disseminated intraalveolar carcinoma, especially bronchiolo-alveolar carcinoma.

Adenocarcinoma↗
PubMed1985

Spectral sensitivity of the freshwater turtle Pseudemys scripta elegans: evidence for the filter-effect of colored oil droplets.

Spectral sensitivity was measured in the light adapted state for two individuals (S1 and S2) of Pseudemys scripta elegans using a behavioral training technique. The curves have three pronounced maxima at 450 nm, at 570 nm (S1) or 540 nm (S2), and at 640 nm. The spectral sensitivity functions can be described by the over-envelope of the effective cone sensitivity functions which are determined by the absorption spectra of the cone photopigments (lambda max at 450, 518 and 620 nm) and by the filter properties of the colored oil droplets.

Adaptation, Ocular↗
PubMed1985

[Combination of transbronchial lung biopsy and bronchoalveolar lavage in disseminated lung diseases].

The effectiveness of transbronchoscopic lung biopsy (TBLB) in combination with bronchoalveolar lavage (BAL) is presented in 487 patients with disseminated lung diseases. The techniques of both methods are described and the results discussed. Comparison of both methods shows that they supply each other. Therefore they should be used in combination in suspected case of disseminated lung disease. Beyond that BAL is important for the control of the disease's course. In the described technique of TBLB we found complications in 7,8%, while with BAL no essential complication was registered.

Biopsy↗