Verhalten von Holo-, Apo- und Coenzym der Peroxidase beim Erhitzen

Zusammenfassung Das thermische Verhalten der beiden Komponenten von Meerrettich-Peroxidase — des Apoenzyms und der prosthetischen Gruppe — wurde mit dem des Holoenzyms verglichen. Daraus wird geschlossen, daß die thermische Inaktivierung der Peroxidase in wäßriger Lösung nicht nur als Resultat einer Veränderung des Apoproteins angesehen werden kann. Vielmehr muß die gesamte dreidimensionale Struktur unter Einschluß der prosthetischen Gruppe in Betracht gezogen werden. Die Inaktivierungsvorgänge beim Holoenzym werden spektralphotometrisch verfolgt, wobei beobachtet wurde, daß die Extinktionsänderung der Soret-Bande mit der Verminderung der Enzymaktivität beim Erhitzen parallel geht. Da ein Wiederanstieg der Soret-Absorption im Verlaufe der Lagerung festgestellt und gleichzeitig eine Regenerierung der Enzymaktivität beobachtet wurde, ist die Änderung der Soret-Absorption beim Erhitzen die Folge sowohl reversibler als auch irreversibler Denaturierungsprozesse.

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The reaction of holo-, apo- and coenzyme of the peroxidase to heating

Summary The thermal reaction of the two components of the horseradish peroxidase—the apoenzyme and the prosthetic group—with that of the holoenzyme were compared. From this we conclude that the thermal inactivation of the peroxidase in aqueous solution is not caused by a change of the apoprotein alone, but rather by participation of the entire three-dimensional structure including the prosthetic group. Spectrophotometric studies of the inactivation process in the holoenzyme revealed that the absorbance of the Soret band changes parallely to a reduction of the enzyme activity during heating. Since it has been found that the Soret absorption increases again during storage and simultaneously the enzyme activity regenerates, the change of the Soret absorption during heating can be regarded as the result of both reversible and irreversible denaturation processes.

     

Einflu? der UV-Bestrahlung auf die freien, nicht eiwei?gebundenen Aminos?uren der Milch

Zusammenfassung Sowohl bei der UV-Bestrahlung der Milch als auch der des Milchserums (etwa 0,01 W/ml) wird im Gegensatz zur Bestrahlung wäßriger Lösungen reiner Aminosäuren insgesamt eine Zunahme an freien Aminosäuren beobachtet. Der Effekt, der auf einer Spaltung von Peptid-Bindungen beruht, ist bei der unter molkereimäßigen Bedingungen durchgeführten UV-Bestrahlung zum Zwecke der Vitamin D-Anreicherung so gering, daß er ernährungsphysiologisch ohne Bedeutung sein dürfte. Die Aminosäuren wurden durch Säulenchromatographie nachMoore undStein bestimmt.     

Experimental and theoretical study of light scattering by individual mature red blood cells by use of scanning flow cytometry and a discrete dipole approximation

Elastic light scattering by mature red blood cells (RBCs) was theoretically and experimentally analyzed by use of the discrete dipole approximation (DDA) and scanning flow cytometry (SFC), respectively. SFC permits measurement of the angular dependence of the light-scattering intensity (indicatrix) of single particles. A mature RBC is modeled as a biconcave disk in DDA simulations of light scattering. We have studied the effect of RBC orientation related to the direction of the light incident upon the indicatrix. Numerical calculations of indicatrices for several axis ratios and volumes of RBC have been carried out. Comparison of the simulated indicatrices and indicatrices measured by SFC showed good agreement, validating the biconcave disk model for a mature RBC. We simulated the light-scattering output signals from the SFC with the DDA for RBCs modeled as a disk-sphere and as an oblate spheroid. The biconcave disk, the disk-sphere, and the oblate spheroid models have been compared for two orientations, i.e., face-on and rim-on incidence, relative to the direction of the incident beam. Only the oblate spheroid model for rim-on incidence gives results similar to those of the rigorous biconcave disk model.     

Dimensionierung von Kristallisatoren

Current status of crystallizer design . This paper surveys current knowledge in designing large scale crystallizers. The volume of a crystallizer depends on the desired mean crystal size, the suspended magma density and the permissible supersaturation, the latter determining the growth velocity and the nucleation rate. Different techniques for measuring the rate of crystal growth are outlined, as are also the methods used in its calculation, which are based upon various models of crystal growth. In designing a large scale crystallizer the phenomena of fluid dynamics and heat transfer must be taken into consideration. The paper deals with these two areas in detail and discusses problems associated with the control of population balance in the slurry.     

Flame-Made Pt/K/Al2O3 for NO x Storage–Reduction (NSR) Catalysts

High surface area Pt/K/Al₂O₃ catalysts were prepared with a 2-nozzle flame spray method resulting in Pt clusters on γ-Al₂O₃ and amorphous K storage material as evidenced by Raman spectroscopy. The powders had a high NO _x storage capacity and were regenerated fast in a model exhaust gas environment. From 300 to 400 °C no excess NO _x was detected in the off gas during transition from fuel lean to fuel rich conditions, resulting in a highly effective NO _x removal performance. Above 500 °C, the NSR activity was lost and not recovered at lower temperatures as K-compounds were partially crystallized on the catalyst.     

Magnetically separable Pt catalyst for asymmetric hydrogenation

A magnetic Pt/SiO₂/Fe₃O₄ catalyst consisting of chirally modified platinum supported on silica coated magnetite nanoparticles was prepared using an easy synthetic route and successfully applied for the enantioselective hydrogenation of various activated ketones. The magnetic catalyst modified with cinchonidine showed a catalytic performance (activity, enantioselectivity) in the asymmetric hydrogenation of various activated ketones in toluene comparable to the best known Pt/alumina catalyst used for these reactions. The novel catalyst can be easily separated from the reaction solution by applying an external magnetic field and recycled several times with almost complete retention of activity and enantioselectivity.