Buchbesprechungen

Ohne Zusammenfassung     

Polarisationsmikroskopischer Nachweis der Anteile von Stechapfel-Samen im Buchweizenmehl

Zusammenfassung Es wird an Mikroaufnahmen gezeigt und beschrieben, wie sich mittels der polarisationsmikroskopischen Untersuchung zwischen gekreuzten Nicolschen Prismen oder Polarisationsfiltern die Zellelemente des Buchweizens von denen des Stechapfels auf Grund der beiden eigenen charakteristischen Strukturen leicht unterscheiden und Verunreinigungen des Buchweizenmehles mit den Samen des Stechapfels leicht erkennen lassen.     

Implementation approach to parallel systems

Parallel system (problem), computation history, concurrency matrix, scheduling discipline     

Buchbesprechungen

Ohne Zusammenfassung     

Addressing the challenge of changing the specificity of RNase T1 with rational and evolutionary approaches

Although ribonuclease T1 (RNase T1) is one of the best-characterized proteins with respect to structure and enzymatic action, numerous attempts at altering the specificity of the enzyme to cleave single-stranded RNA at the 3'-side of adenylic instead of guanylic residues by rational approaches have failed so far. Recently we generated and characterized the RNase T1 variant RV with a 7200-fold increase in adenylyl-3',5'-cytidine (ApC)/guanylyl-3',5'-cytidine (GpC) preference, with the guanine-binding loop changed from 41-KYNNYE-46 (wt) to 41-EFRNWN-46. Now we have introduced the asparagine residue at position 46 of the wild-type enzyme as a single-point mutation in variant E46N and in combination with the Y45W exchange also occurring in RV. Both variants show an improved ApC/GpC preference with a 1450-fold increase for E46N and a 2100-fold increase for Y45W/E46N in comparison to wild-type activity. We also addressed the challenge of altering enzyme specificity with an evolutionary approach. We have randomly introduced point mutations into the RNase T1 wild-type gene and into the gene of the variant RV with different mutation rates. Altogether we have screened about 100,000 individual clones for activity on RNase indicator plates; 533 of these clones were active. A significant change in substrate specificity towards an ApC preference could not be observed for any of these active variants; this demonstrated the magnitude of the challenge to alter the specificity of this evolutionary perfected enzyme.     

Polarisationsmikroskopischer Nachweis von Maismehl in anderen Getreidemehlen

Zusammenfassung Auf Grund der starken Doppelbrechung der Partikel des Horn-Endosperms im Maismehl im polarisierten Licht zwischen gekreuzten Polarisatoren wird eine Methode zum qualitativen Nachweis von Maismehl in anderen Getreidemehlen beschrieben.     

Zur Kinetik der Reaktionsschichtbildung an Reinsteisen bei mechanischer Bearbeitung (Simulation von Erosionskorrosion)

Contribution to the kinetics of the formation of reaction layers on high purity iron during mechanical machining (simulation of erosion-corrosion) Under the effect of working with impact bodies passivation kinetics of high purity iron in neutral phosphate electrolytes is considerably modified. Under potentio-dynamic conditions a reaction layer is formed by the mechanical treatment prior to the passivation layer. The kinetics of formation of this layer is studied in terms of current density vs. time at constant potential. In this connection the time dependence is derived for the different partial currents. The mechanical working initiates a two-dimensional proressive nucleation which can be interpreted in terms of reactions between freshly generated iron surfaces with the electrolyte.