Sulfite formation by wine yeasts

The enzyme catalyzing the reduction of sulfite by reduced benzyl viologen (BVH) was partially purified and characterized from two strains of wine yeasts, a sulfite-producing strain and a non-producing strain.Both enzymes showed corresponding features in pH-optima, optima of buffer and benzyl viologen concentrations.The enzymes did not catalyze the reduction of nitrite by reduced viologen dyes, but the reduction of sulfite was uncompetitively inhibited by nitrite. Compounds of sulfur metabolism such as sulfate, thiosulfate, cysteine, serine and methionine did not influence the activity of either of the enzymes. The main differences between the two enzymes exist in the specific activities in crude extracts, the K _m -values for sulfite, substrate inhibition rates, and localization in different fractions during (NH₄)₂SO₄ precipitation. The specific activity in crude extracts of the sulfite-producing strain (0.052 moles S^2- x min^-1 x mg^-1) was about three fold higher than that of the non-producing strain (0.0179 moles S^2- x min^-1 x mg^-1). On the other hand the sulfite-producing strain had a higher K _m -value for sulfite (2×10^-3 M) and was more strongly inhibited by the substrate than the non-producing strain (6×10^-3 M).     

The mechanism of electrical breakdown in the membranes ofValonia utricularis

Summary The dielectric breakdown in the membranes of cells ofValonia utricularis was investigated using intracellular electrodes and 500-sec current pulses. Electrical breakdown, which occurs when the membrane potential reaches a well-defined critical value, is not associated with global damage to the cell or its membranes (the membrane reseals in <5 sec). It was thus possible to investigate the effect of temperature on dielectric breakdown in single cells. It was found that the critical potential for breakdown was strongly dependent on temperature, decreasing from 1000 mV at 4°C to 640 mV at 30°C. The decrease in the breakdown potential with increasing temperature and the very short rise-time of the breakdown current (1 sec) suggests that the Wien field dissociation does not play a major role in the breakdown process. It is shown that the nonlinearI–V characteristics observed at different temperatures can be accurately accounted for with no adjustable parameters, by considerations of the mechanical compression of the membrane due to stresses induced by the electric field. Electrical breakdown on this scheme results from an electromechanical instability in the membrane. On this basis the present results indicate that the elastic modulus of the region of the membrane where breakdown occurs, decreases by a factor of 2 with increasing temperature from 4 to 30°C. On the assumption of a thickness of 4.0 nm and a dielectric constant of 5, the elastic modulus is estimated to have a value of 5×10⁶ Nm^–2 at 20°C.     

Mitomycin und ein neues Phenoxazon-Pigment aus Streptomyces michiganensis

Streptomyces michiganensis strain Tü 1074, was isolated from a Tunesian soil sample and produces in liquid medium an antibiotic active pigment complex. Besides mitomycin A the separation of this complex yielded a nonactive phenoxazone, which hitherto has not been described in the literature. In contrary to all known phenoxazones from microorganisms the new compound lacks a 2-amino-function. The production of this phenoxazone could be enhanced by optimizing the conditions of fermentation.     

Der frühlarvale Köcherbau von Micrasema longulum McL. (Trichoptera,Brachycentridae)

Case Construction of Young Larvae of Micrasema longulum McL. (Trichoptera, Brachycentridae) The method of case building used by the first three larval instars of Micrasema longulum is described. The initial case is constructed above the hatching aperture in the jelly of the egg mass, in the same way as it is done by other species of Brachycentridae. The material of the initial case is caught from drifting particles in running water. From the end of the first larval instar only silk is used for the extension of the case. Two silken layers of a very regular pattern are to be distinguished. The construction of the cloverleaf-shaped posterior aperture is described. Some of the methods used for the case building show a maturing process during ontogenesis.     

Die Chromosomenzahlen in den Leberzellen von Ratten verschiedenen Alters

Ohne ZusammenfassungMit Unterstützung der Deutschen Forschungsgemeinschaft.     

New insights in the cellular processing of platinum antitumor compounds, using fluorophore-labeled platinum complexes and digital fluorescence microscopy

The cellular distribution and processing pathways of two platinum compounds, modeling the antitumor drug cisplatin (cDDP) in human osteosarcoma (U2-OS) cells is reported. A [Pt(en)Cl] entity has been covalently linked to a carboxyfluorescein diacetate (CFDA) moiety and to a dinitrophenyl (DNP) moiety. The two different constructs were administered to living cell cultures that were analyzed using digital fluorescence microscopy. The non-fluorescent CFDA construct becomes fluorescent after cellular uptake and subsequent acetate hydrolysis by esterases, and is therefore suitable to monitor platinum in living cells; the DNP construct can be visualized by immunocytochemistry and consequently serves as a control. Both complexes were readily internalized by the cells, and localized throughout the whole cell. After 2-3 h the complex accumulated in the nucleus, but 6-8 h after incubation a punctuate staining of a cytoplasmic region was observed, that persisted and became more pronounced after 24 h. The overall fluorescence in the cell decreased over time, implying a secretion of the platinum complex. Surprisingly, the accumulation remained visible after 72 h. Co-localization experiments with a Golgi apparatus-selective stain indicate the involvement of Golgi vesicles in intracellular processing of cisplatin-derived complexes. Immunocytochemical studies, using the DNP derivative, resulted in very similar images as obtained with the CFDA construct. CFDA-boc (a non-platinum-containing fluorescein derivative) was used as control: a faint staining throughout the whole cell was observed. Cisplatin-resistant U2-OS/Pt cells showed staining patterns very similar to the U2-OS cells using both platinum constructs. This study illustrates that only a very small portion of the platinum complex eventually remains bound to DNA, as after 24 h no significant fluorescence could be observed in the nucleus. Cisplatin-derived complexes with fluorescent tags afford a new insight into the cellular processing of these complexes and therefore may contribute to further unraveling of the mechanism of platinum antitumor complexes.