Recipient competence in F''lac matings of Escherichia coli K-12.

We studied recipient mating ability in the presence of excess F'lac donors. Ninety-five percent of recipients were able to receive F'lac in 30-min matings. Competition between an F'-lac donor and an F'lac traI donor, which mobilized a ColE1 derivative (pML2), showed that each recipient mated with an average of two to three donors in 30 min. Experiments in which the competing donor was added at different times showed that some competition occurred throughout the 30-min mating period, which suggested that aggregate formation was spread over this time.     

Stable Defined Substrate for Turbidimetric Assay of Endoxylanases

A stable xylan suspension was prepared and characterized. Hydrolysis of the particles converts them into soluble fragments, thereby lowering the turbidity of the suspension. The small volume of the assay mixture, the short incubation time required, and the simplicity of the procedure permit the rapid analysis of many samples. Furthermore, the procedure can be used to assay xylanase activities in the presence of other reducing materials and is also useful for monitoring low-level xylanase activities.     

Production and initial characterisation of the xylan-degrading system of Phanerochaete chrysosporium

We report the optimum conditions for the degradation of oat spelt arabinoxylan and a preliminary characterisation of the inducible xylan-degrading system of the lignin-degrading white-rot fungus Phanerochaete chrysosporium. Xylanase activity was optimal at pH 5.0 and 50°C; see attached sheet the maximum reaction velocity (V_max) of the system was 3.86 units (U) mg^–1 protein with arabinoxylan as substrate and the substrate concentration giving half V_max (S_0.5) was 0.52 mg ml^–1. At concentrations of arabinoxylan greater than 15 mg ml^–1 excess substrate inhibition was observed. Xylose at 0.9 mm inhibited activity to the extent of 50%. Xylanase activity increased as a function of the dilution of the enzyme preparation prior to assay. It was resolved into four peaks by using a DEAE-Biogel column; the material in these peaks differed with respect to xylan solubilisation and the formation of reducing sugars. Electrofocusing gels allowed visualisation of several bands of activity corresponding to each peak. The arabinoxylan degradation system of P. chrysosporium is therefore composed of multiple components. Correspondence to: P. Broda     

Fast phototaxis and electroretinograms in red-eyed and white-eyed retinal degeneration mutants of Drosophila melanogaster

Due to the presence or absence of screening pigments red-eyed and white-eyed Drosophila melanogaster have electroretinograms with different sensitivity spectra (Stark and Wassermann, 1974). The same differences were found in a comparison of ERGs of red-eyed and white-eyed retinal degeneration mutants. No effect of the pigments can, however, be found in the spectral sensitivity of escape phototaxis behaviour. The observations imply that only receptor cells in on-axis ommatidia contribute to this behaviour even in the white-eyed fly.     

R Plasmids R91 and R91a from Pseudomonas aeruginosa Share Only the Gene for Carbenicillin Resistance

Plasmid R91a of Pseudomonas aeruginosa strain 9169 is homologous with RP1. Plasmid R91 carried by the same strain is related in the Tn1 region but is otherwise unrelated to R91a.     

The beginning of photosynthesis

There is no evolutionary continuity between photochemical abiosynthesis and bacterial photosynthesis. Rather, the photosynthetic bacteria are descendants of fermenters that did not use light. Photosynthesis and respiration, both using electron flow coupled with phosphorylation, have a common origin (conversion hypothesis), but photosynthesis came first. Anaerobic (nitrate or sulphate) respiration cannot have preceded photosynthesis as neither nitrate nor sulphate existed on the early earth. Sulphate was made first by photosynthetic sulphur bacteria. Nitrate arose even later, namely, in the aerobic biosphere produced by the blue-green algae, the first phytotrophs. Photophosphorylation may have originated through the combination with membrane function of substrate level phosphorylation in reactions of photoproducts. Cyclic photophosphorylation arose while the biosphere was still reducing. It was supplemented later by processes for the light-based production of reducing power (NADH), ATP-powered electron flow, and subsequently light-powered electron flow with ATP production (noncyclic photophosphorylation). These later processes served the assimilation of CO₂.     

Der freie Raum synchroner Chlorella

Zusammenfassung Der freie Raum innerhalb der Zellwand von Chlorella fusca wurde nach einer Verdünnungsmethode mit ¹⁴C-mannit bestimmt. ³⁶Cl-Perchlorat ist wegen des Donnan-Effekts weniger geeignet. Korrektur für außen anhaftendes Wasser wurde mit ¹⁴C-Dextran durchgeführt. Während der Lichtphase (16 Std) des Wachstumscyclus nimmt der freie Raum von 11 auf 4% des Zellvolumens ab, und er nimmt während der ersten 8 Std der Dunkelphase (12 Std) wieder zu. Während der Lichtphase vermindert sich, nach dem Volumen des freien Raums zu urteilen, die Zellwanddicke; offenbar bleibt die Zellwandsynthese gegenüber dem Zellwachstum zurück.

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The free space of synchronous Chlorella

Summary The free space in the cell wall of Chlorella fusca has been determined by a dilution method with ¹⁴C-mannitol. Owing to a Donnan effect, ³⁶Cl-perchlorate is less suitable, ¹⁴C-dextran was used to correct for external water. During the light phase (16 h) of the generation cycle, the free space decreases from 11 to 4% of the cell volume. It increases again during the first 8 h of the dark phase (12 h). During the light phase, the cell wall, as judged by the free space volume, thins; apparently cell wall synthesis does not fully kepp in step with cell growth.

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Herrn Prof. Dr. O. Kratky zum 70. Geburtstag gewidmet.     

The begginning of photosynthesis.

There is no evolutionary continuity between photochemical abiosynthesis and bacterial photosynthesis. Rather, the photosynthetic bacteria are descendants of fermenters that did not use light. Photosynthesis and respiration, both using electron flow coupled with phosphorylation, have a common origin ('conversion hypothesis'), but photosynthesis came first. Anaerobic (nitrate or sulphate) respiration cannot have preceded photosynthesis as neither nitrate nor sulphate existed on the early earth. Sulphate was made first by photosynthetic sulphur bacteria. Nitrate arose even later, namely, in the aerobic biosphere produced by the blue-green algae, the first 'phytotrophs'. Photophosphorylation may have originated through the combination with membrane function of substrate level phosphorylation in reactionsand function of substrate level phosphorylation in reactions of photoproducts. Cyclic photophosphorylation arose while the biosphere was still reducing. It was supplemented later by processes for the light-based production of reducing power (NADH), ATP-powered electron flow, and subsequently light-powered electron flow with ATP production (noncyclic photophosphoryaltion). These later processes served the assimilation of CO2.