[Xylose isomerase constitutive biosynthesis in Arthrobacter nicotianae].

The specific features of biosynthesis of the cell-bound xylose isomerase by the actinobacterium Arthrobacter nicotianae BIM V-5 were studied. It was demonstrated that the constitutive synthesis of this enzyme in the studied bacteria, not subject to catabolite repression, was inhibited by xylulose, an intermediate product ofxylose utilization and the final product of its enzymatic isomerization. Short-term experiments demonstrated that xylulose at a concentration of 0.005% almost completely repressed the xylose isomerase synthesis in A. nicotianae. This effect was independent of the time moment when the repressor was added to the cultivation medium and was not associated with its influence on the catalytic activity of the enzyme.

[Catalytical properties of Arthrobacter nicotianae cells, a producer of glucose isomerase, immobilized in xerogel of silicium dioxide].

Arthrobacter nicotinanae cells, producers of glucose isomerase, were immobilized in xerogel of silicium dioxide, and properties of the resulted heterogeneous biocatalysts were investigated in the process of isomerization of monosaccharide (glucose and fructose). The glucose isomerase activity of the resulted biocatalysts was shown to be 10 U/g, on average, taking into account the loss of the activity upon the immobilization, which amounted to 50% of the cell activity in suspension. The rate of the fructose isomerization increased linearly in the range of 55-80 degrees C with the temperature coefficient 1.3. The biocatalysts were stable in this range; they were rapidly inactivated, however, at increasing temperature. The half-inactivation time was six to seven h and five min or less at 80 degrees C and 85 degrees C, respectively. The half-inactivation time of heterogeneous biocatalysts was 50-90 h in the periodic process of isomerization of 2 M monosaccharides at 60 degrees C in the presence of the immobilized Arthrobacter nicotinanae cells.

[Catabolite repression of xylose isomerase synthesis in Arthrobacter ureafaciens].

The effect of a specific substrate as well as other carbon sources on the biosynthesis of xylose isomerase in the actinobacterium Arthrobacter ureafaciens BIM B-6 has been studied. It was established that xylose and its structural analogue xylite induced the production of the enzyme by bacterial cells. The inducing effect peaked at a concentration of specific substrates of 0.025% (as carbon) and then remained unchanged irrespective of the substrate amount. It has been shown that the synthesis of xylose isomerase by A. ureafaciens is controlled by catabolite repression occurring at the transcription level and mediated by cyclic 3',5'-AMP.