Numerical calculations of the pH of maximal protein stability. The effect of the sequence composition and three-dimensional structure.

A large number of proteins, found experimentally to have different optimum pH of maximal stability, were studied to reveal the basic principles of their preference for a particular pH. The pH-dependent free energy of folding was modeled numerically as a function of pH as well as the net charge of the protein. The optimum pH was determined in the numerical calculations as the pH of the minimum free energy of folding. The experimental data for the pH of maximal stability (experimental optimum pH) was reproducible (rmsd = 0.73). It was shown that the optimum pH results from two factors - amino acid composition and the organization of the titratable groups with the 3D structure. It was demonstrated that the optimum pH and isoelectric point could be quite different. In many cases, the optimum pH was found at a pH corresponding to a large net charge of the protein. At the same time, there was a tendency for proteins having acidic optimum pHs to have a base/acid ratio smaller than one and vice versa. The correlation between the optimum pH and base/acid ratio is significant if only buried groups are taken into account. It was shown that a protein that provides a favorable electrostatic environment for acids and disfavors the bases tends to have high optimum pH and vice versa.     

Über das führende Zentrum im Herzen von Testudo graeca L.

Zusammenfassung Die einzelnen Anteile des venösen Vorherzens sind bei der Schildkröte untereinander nicht ganz gleichwertig. Als Schrittmacher des Herzens funktioniert in der Norm die Einmündungsstelle der rechten oberen Hohlvene in den Sinus. Von dort aus empfangen die Hohlvenen ihre Antriebe zur Tätigkeit. Da die rechte obere Hohlvene dieser Stelle näher gelegen ist als die linke, so erklärt sich, daß beim Schildkrötenherzen die rechte obere Hohlvene in ihrer Tätigkeit der linken für gewöhnlich vorangeht.Die automatischen Eigenschaften des venösen Vorherzens sind bei der Schildkröte im Gegensatz zu den Amphibien nicht an allen Stellen gleichmäßig entwickelt. Mit höchster Automatie ist der Sinus an der Einmündungsstelle der rechten oberen Hohlvene ausgerüstet. Es folgen dann die Hohlvenen in der Reihenfolge: rechte obere, linke obere und untere Hohlvene.Durch Erwärmung der verschiedenen Anteile des venösen Vorherzens, besonders der oberen und unteren Hohlvene ist man imstande eine Frequenzzunahme des ganzen Herzens zu bewirken. Doch tritt diese niemals so rasch ein und ist auch niemals in so hohem Maße ausgeprägt, wie wenn man jene ventral gelegenen Partien des Sinus erwärmt, die der rechten oberen Hohlvene benachbart sind. Man kann also schon beim Schildkrötenherzen von einer gewissen Differenzierung in der Anlage der führenden Stelle sprechen. Doch geht diese noch nicht so weit, daß nicht etwa auch andere Stellen die Führung des Herzens übernehmen könnten, falls das Hauptzentrum versagt. Man beobachtet vielmehr in völliger Übereinstimmung mit den Ergebnissen örtlich ungleicher Erwärmung der einzelnen Anteile des venösen Vorherzens, daß beim Versagen des Hauptzentrums sofort ein anderer Teil einzutreten vermag. Dies äußert sich einfach darin, daß ein Wechsel in der Schlagfolge von rechter und linker oberer Hohlvene eintritt. Es geht dann nicht mehr die rechte obere in der Tätigkeit der linken voran, sondern es arbeiten entweder beide Venen gleichzeitig öder aber es arbeitet die linke obere Hohlvene vor der rechten.Herrn Prof. Dr. Adolf Loewy, dem Leiter des Schweizerischen Forschungsinstituts, sage ich auch an dieser Stelle meinen ergebensten Dank für seine freundliche Aufnahme und tatkräftige Unterstützung.     

Identification by Tn10 transposon mutagenesis of host factors involved in the biosynthesis of K99 fimbriae of Escherichia coli: Effect of LPS core mutations

Abstract Tn 10 transposon mutagenesis of Escherichia coli producing K99 fimbriae was carried out to identify host factors involved in regulation or biosynthesis of fimbriae. Two chromosomal mutants were obtained that showed a strongly reduced cell surface expression of K99 fimbriae upon colony blotting and ELISA. Analysis by inversed PCR and nucleotide sequencing showed that one mutant (EP14) contained the Tn 10 transposon in rfaQ , affecting theexpression of the rfaQGP gene cluster, whereas the other mutant (EP35) was affected in a, to date, unknown region of the genome. Immunoblotting analysis confirmed a Rd₁ type of LPS of mutant strain EP14. These findings for the first time indicated an effect of LPS core biosynthesis on the biogenesis of fimbriae at the cell surface. Preliminary experiments indicated that K99 major subunits, in contrast to K88 subunits, strongly bind LPS molecules.     

The allianceFimbristylidion dichotomae in Iraq

On silt deposits in river beds around Baghdad a new association, theCrypsidi-Fimbristylidetum was found, belonging to the allianceFimbristylidion dichotomae. As the period when river beds are bare, lasts about half a year, the life of this community is very short, but it appears anew every year. It produces about 80 g/m²/year dry wieght of biomass.     

Increase of free Mg<Superscript>2+</Superscript>in the skeletal muscle of chronic fatigue syndrome patients

In a previous study we evaluated muscle blood flow and muscle metabolism in patients diagnosed with chronic fatigue syndrome (CFS). To better understand muscle metabolism in CFS, we re-evaluated our data to calculate free Magnesium levels in skeletal muscle. Magnesium is an essential cofactor in a number of cell processes. A total of 20 CFS patients and 11 controls were evaluated. Phosphorus magnetic resonance spectroscopy from the medial gastrocnemius muscle was used to calculate free Mg²⁺ from the concentrations and chemical shifts of Pi, PCr, and beta ATP peaks. CFS patients had higher magnesium levels in their muscles relative to controls (0.47 + 0.07 vs 0.36 + 0.06 mM, P < 0.01), although there was no difference in the rate of phosphocreatine recovery in these subjects, as reported earlier. This finding was not associated with abnormal oxidative metabolism as measured by the rate of recovery of phosphocreatine after exercise. In summary, calculation of free Mg²⁺ levels from previous data showed CFS patients had higher resting free Mg²⁺ levels compared to sedentary controls.     

Characteristics of the rRNA synthesis taking place at low temperatures in wheat cultivars with varying degrees of frost hardiness

The characteristics and intensity of rRNA synthesis occurring at temperatures around freezing point were examined in connection with frost hardiness in wheat cultivars. The intensity of rRNA synthesis taking place near freezing point showed a close positive correlation with the critical temperature (LT₅₀) characteristic of the frost resistance of the varieties. The quantity of high MW precursors to rRNA appears to be heterogeneous in hardy and non hardy varieties at low temperatures and point primarily to an inhibition in the maturation processes of ribosomes in the final nuclease processing step in non-frosthardy varieties.