Regulation and physiological role of cyanide-resistant oxidases in fungi and plants.

Data on the induction and regulation of cyanide-resistant oxidases in eucaryotic microorganisms and higher plants are reviewed. Expression of an alternative oxidase gene can be caused by a decrease in energy charge in cells. Some evidence exists suggesting that cAMP and Ca2+ act as intracellular signals inducing the expression of the alternative oxidase genes. Under certain conditions cells produce alternative oxidases which remain in an inactive state. Activation of the alternative pathway of cell respiration is usually observed when electron transport via cytochromes is inhibited. The physiological role of the alternative oxidase is discussed.

Kinetic model of hydrocortisone 1-en-dehydrogenation by Arthrobacter globiformis.

A kinetic model of the hydrocortisone-to-prednisolone transformation by Arthrobacter globiformis is constructed using the experimental data obtained in studies of this process. Besides adequately describing experimental data, the model allows one to determine the relation between hydrocortisone oxidation and the level of endogenous substrates in bacterial cells, and the relation between the saturating concentration of hydrocortisone in the enzymic system of bacteria and the content of endogenous substrates in their cells, as well as the regulation of the transmembrane potential and the activation by the uncouplers.

Kinetic model for the regulation of redox reaction in steroid transformation by Arthrobacter globiformis cells.

A kinetic model of hydrocortisone transformation was developed in studies of the kinetics of biochemical systems. The regulatory bases of the model are the biosynthesis of steroid-transforming enzymes and their activity, the level of endogenous substrates, the respiratory chain activity, and the initial concentrations of reagents. When compared, the experimental data completely coincide with the results of the computer modeling, the coincidence being not only qualitative but also quantitative. It indicates that the model suggested can be used for further studies of other transformations of steroid compounds, as well as for transformation of steroid compounds under close-to-biotechnological conditions. The results obtained by means of this model permit one to trace in dynamics the behavior of a number of parameters characterizing the process which is very difficult or not feasible to do in a biochemical experiment. The following was shown: (1) the behavior of the respiratory chain (the reversible transition of its oxidized and reduced forms); (2) the change of the transmembrane potential of hydrogen ions within a far larger stretch of time than is feasible to register in a biochemical experiment; (3) the regulation of the activity of 20beta-hydroxysteroid dehydrogenase and 1, 2-reductase not only by the change in the level of endogenous substrates, but also by means of their biosynthesis; and (4) the regulatory role of 3-ketosteroid-1-en-dehydrogenase.

Redox reactions in hydrocortisone transformation by Arthrobacter globiformis cells.

Hydrocortisone and prednisolone transformation by Arthrobacter globiformis cells in aerobic and anaerobic conditions was studied. 3-Ketosteroid-1-en-dehydrogenase activity was shown to be the major factor regulating the direction of transformation. When it is high (aerobic conditions), the end products of hydrocortisone transformation are prednisolone or its 20 beta-hydroxy derivative. The latter is produced via 1-en-dehydrogenation, which is not a limiting stage of the process. Low 3-ketosteroid-1-en-dehydrogenase activity (in the presence of cyanide) or its complete inhibition (strictly anaerobic conditions) result in the direct reduction of 20-keto group of hydrocortisone.

Regulation of 3-ketosteroid-1-en-dehydrogenase activity of Arthrobacter globiformis cells by a respiratory chain.

It has been shown that 3-ketosteroid-1-en-dehydrogenase localized in a cytoplasmic membrane donates reducing equivalents to a respiratory chain directly which passes them over to oxygen. Microbial hydrocortisone oxidation is coupled with energy generation in the form of the H+ transmembrane potential. Electron transfer via a respiratory chain is the limiting stage in the process of hydrocortisone 1-en-dehydrogenation.

[Steroid transformation using immobilized microorganisms. II. Degradation of the sidechain of cholesterol by immobilized cells of Nocardia erythropolis]. / Steroid transformation mit immobilisierten Mikroorganismen. II. Abbau der Seitenkette von Cholesterol mit immobilisierten Zellen von Nocardia erythropolis.

The degradation of cholesterol side chain was studied by immobilized cells of Nocardia erythropolis in the presence of an inhibitor of the microbial steroid-skeleton-degradation. Different immobilized preparations such as DEAE-cellulose adsorbates, ionic cross-linked polymer gels, i.e., Al/Coalginates and polyacrylates, respectively, and polyethylene maleic acid anhydride supports have shown a high transformation activity yielding the C22- and C19-degradation products. No side chain degradation activity could be observed after immobilization of the cells in polyacrylamide gel under usual conditions caused by the toxic effect of the acrylamide monomer on the Nocardia cells.