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K Müller

Publications and source records attributed to K Müller.

At least 361 records · Page 20Linked to original sources
PubMed1984

E. coli aspartokinase II-homoserine dehydrogenase II polypeptide chain has a triglobular structure.

E.coli aspartokinase II-homoserine dehydrogenase II is, as aspartokinase I-homoserine dehydrogenase I, composed of three globular domains: the N-terminal domain is endowed with kinase activity; the C-terminal domain carries the dehydrogenase activity. These two parts of the polypeptide chain are separated by a central inactive domain. Thus, the polypeptide chains of the two multifunctional proteins are homologous not only in their sequence but also in their triglobular domain structure.

Aspartokinase Homoserine Dehydrogenase↗
PubMed1984

The interaction between Escherichia coli aspartokinase-homoserine dehydrogenase and 3-acetylpyridine-adenine dinucleotide phosphate (reduced), an analog of NADPH.

The interaction of 3-acetylpyridine-adenine dinucleotide phosphate, a structural analog of NADPH, with aspartokinase-homoserine dehydrogenase has been studied by fluorescence and activity measurements. This analog binds to the same site and with the same affinity as does the natural coenzyme. Also, the binding of homoserine to the dehydrogenase site or that of threonine to the regulatory site is the same whether NADPH or its analog is bound to the enzyme. So NADPH and its analog appear as equivalent in the formation of various stable enzyme-ligand(s) complexes. The analog resembles NADPH enough so that it is a substrate that the enzyme can use to reduce aspartate semialdehyde; the maximum velocity of this dehydrogenase reaction is however reduced by 90% as compared to that with NADPH. It seems as if one of the catalytic steps is affected by the replacement of a--CONH2 group by--COCH3. Another difference between the two coenzymes is that the reaction with the analog is insensitive to threonine, whereas that with NADPH is inhibited. The lack of inhibition is not due to a lack of binding, but rather to a difference in the ternary complexes composed of enzyme, coenzyme, and substrate. A possible relationship between the inhibition by threonine and the mechanism of the dehydrogenase reaction is thus suggested by this comparison between NADPH and its analog.

Aspartokinase Homoserine Dehydrogenase↗
PubMed1984

Stepwise inactivation of Escherichia coli aspartokinase-homoserine dehydrogenase I.

In the range of guanidine hydrochloride concentrations from 0.2 to 1.2 M, aspartokinase-homoserine dehydrogenase I loses its enzymatic properties, both kinase and dehydrogenase activities and their allosteric inhibition by L-threonine. Ligands which stabilize the tetrameric native structure protect the enzyme against inactivation. Under some conditions, all the functional properties do not disappear at the same rate: an intermediate species possessing only the kinase activity can be detected. Several arguments suggest that this partly active intermediate has a monomeric structure. These results show that deactivation of aspartokinase-homoserine dehydrogenase I is a stepwise process, compatible with the reverse of the previously described reactivation [Garel, J.-R., & Dautry-Varsat, A. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 3379-3383]. The same measurements performed with a monofunctional fragment carrying the dehydrogenase activity show that the loss of dehydrogenase activity is the same whether or not the polypeptide chain is intact or lacks the kinase region; this finding suggests that the protein is composed of independent regions. The influence of protein aggregation in studying unfolding-refolding of oligomeric enzymes is also discussed.

Aspartokinase Homoserine Dehydrogenase↗
PubMed1984

Folding of aspartokinase-homoserine dehydrogenase I is dominated by tertiary interactions.

In the presence of guanidine hydrochloride concentrations above 2 M, aspartokinase-homoserine dehydrogenase I remains sufficiently soluble so that the fluorescence and circular dichroism of the protein can be measured. Both parameters show that, up to 3 M guanidine hydrochloride, the protein exists in a stable folded state which possesses a large amount of secondary structure and buried tryptophan residues. This intermediate species is probably monomeric; it is reversibly unfolded by guanidine hydrochloride concentrations between 3 and 4 M. This folded species is formed rapidly from unfolded protein when the denaturant is diluted out, and this rapid folding step precedes all the reactivation steps described previously. The existence of a stable monomeric and folded intermediate indicates that the tertiary interactions have a major contribution to the stability of the native structure of aspartokinase-homoserine dehydrogenase I. Similar measurements were performed on two complementary nonoverlapping fragments: a kinase fragment corresponding to the N-terminal third and a dehydrogenase fragment corresponding to the C-terminal two-thirds of the polypeptide chain. Both fragments exist in a stable folded state up to 2.5 M guanidine hydrochloride. Both fragments show cooperative unfolding transitions between 2.5 and 4 M denaturant. The stability of the folded state of a given region is about the same in an isolated fragment and in the entire chain of aspartokinase-homoserine dehydrogenase I: indeed, an equimolar mixture of these two fragments and the intact chain would give about the same results. This indicates that folding of the kinase and dehydrogenase regions occurs independent ly with a single subunit of the entire protein.

Aspartokinase Homoserine Dehydrogenase↗
PubMed1984

High pressure dissociation of lactate dehydrogenase from Bacillus stearothermophilus and reconstitution of the enzyme after denaturation in 6 M guanidine hydrochloride.

Tetrameric lactate dehydrogenase from Bacillus stearothermophilus exhibits unusual stability towards high hydrostatic pressure: In contrast to the mesophilic enzyme, incubation at pressures up to 2.8 kbar does not cause irreversible denaturation. Hybridization under these conditions suggests partial dissociation to the dimer, indicating that reassociation occurs within the dead-time after pressure release (less than 20 s at less than or equal to 40 micrograms/ml, 20 degrees C). Incubation at P less than 2.8 kbar affects neither the native quaternary structure nor the catalytic function of the enzyme. Reconstitution of the unfolded and dissociated subunits after denaturation, e.g., in 6 M guanidine . HC1, is characterized by fast association favouring the native assembled structure. Evidence from spectroscopic measurements shows that reconstitution starts with a fast refolding reaction generating a native-like conformation. The subsequent rate-determining transconformation of the "structured monomers" governs the kinetics of reactivation and reassociation as one single first-order process. Chemical crosslinking with glutaraldehyde proves that the "structured monomers" undergo fast association to form the tetrameric final state of reconstitution, with significant amounts of dimeric intermediates being detectable. The renatured enzyme is indistinguishable from the native enzyme regarding its physicochemical and enzymological properties (e.g., activation by fructose-1,6-bisphosphate, and susceptibility towards proteolytic digestion).

Drug Stability↗
PubMed1984

A 1H NMR study of the interactions and conformations of rationally designed brodimoprim analogues in complexes with Lactobacillus casei dihydrofolate reductase.

A consideration of the detailed structural information available from X-ray crystallographic and NMR studies on complexes of dihydrofolate reductase with inhibitors has led to the design of trimethoprim analogues with improved binding properties. Computer graphic techniques have been used to predict which substituent groups were required at the 3'-O position of brodimoprim (2,4-diamino-5-(3,5-dimethoxy-4-bromobenzyl)pyrimidine) to make additional interactions with the enzyme. NMR spectroscopy provided a convenient method of assessing if the analogues were binding in the predicted manner. On the basis of this approach, the C4,C6-dicarboxylic acid analogue IX was designed to interact with Arg-57 and His-28 in the enzyme, and this analogue was found to bind 3 orders of magnitude more tightly than the parent brodimoprim.

Binding Sites↗
PubMed1984

DNA and RNA virus species are inhibited by xanthates, a class of antiviral compounds with unique properties.

Various DNA and RNA virus species are inhibited by xanthate compounds at concentrations that leave the mitotic activity of uninfected cells unimpaired. The concentration of tricyclodecan -9-yl- xanthogenate that reduces the yield of herpes simplex virus types 1 and 2 by 50% is between 4.5 and 33 microM. The replication of DNA viruses such as simian virus 40 can be blocked at the DNA and RNA level both early and late after infection. The xanthates are not incorporated into nucleic acids. Episomal bovine papilloma virus DNA replication and transcription are also inhibited in transformed cells. The treated cells revert to the normal phenotype by acquisition of contact inhibition and a flat morphology.

Antiviral Agents↗
PubMed1984

C-reactive protein and clinical kidney transplantation.

50 patients were serially monitored for C-reactive protein (CRP) in serum after kidney transplantation. Compared with a control group the post-operative peak at days 1 and 3 was strongly depressed in the immunosuppressive-treated transplant group (p less than 0.01). In 29 out of 30 patients CRP concentration showed an average rise from 9.4 to 30.0 micrograms/ml between the 5th and 2nd day before onset of the rejection episodes (p less than 0.01). The dynamics of CRP concentration before, during and after prednisolone anti-rejection bolus therapy was considered in 22 cases. The first bolus led to a greater or smaller decrease in CRP concentration in almost all patients. After the second bolus treatment CRP dropped to zero already in more than half of the patients with reversible rejection episodes (p less than 0.01). In case of irreversible rejection crises CRP never reached zero.

Adult↗
PubMed1984

[Digital image information systems in radiology--status and developmental trends].

A digital image information system is expected to increase the efficiency of image acquisition and reporting. In addition to the requirements of the radiology department the requirements of the wards and the theatres must also be taken into account. The image information system has to be linked with the administrative work flow throughout the department. Therefore, it must provide interfaces to a radiology management system. In the United States such an image information system is referred to as "Picture Archiving and Communication System" = PACS. A suitable systems concept and the requirements of a real system are pointed out. The available technical solutions are discussed as well as the probable trends of future developments.

Computers↗
PubMed1984

Endothelial cell loss enhances the pressor response in resistance vessels.

The role of the endothelium in pressor and relaxation responses was studied using the isolated, perfused mesenteric arterial bed of the rat. Perfusion of mesenteric beds with distilled water for 10 min resulted in endothelial cell loss. This procedure produced no morphological injury to the medial smooth muscle cells as seen by transmission electron microscopy. Such endothelial cell removal resulted in an increase in pressor responses to angiotensin II, epinephrine, norepinephrine and serotonin. Removal of the endothelium either markedly reduced or eliminated the vasodilation response to acetylcholine, whereas it did not alter the vasodilation response to diazoxide. These results show that loss of endothelial cells in resistance vessels results in a marked enhancement of the pressor response to several endogenous vasoconstrictor agents. Thus endothelial cell products may be important in the regulation of local blood flow and resistance. These results could have important implications in disease states in which there might be endothelial cell dysfunction.

Animals↗