Combination of classical dry ashing with stripping voltammetry in trace element analysis of biological materials: review of literature published after 1978.

Critical statements have appeared recently in the literature concerning the need for classical dry ashing in trace element analysis of biological materials. In contrast, respected institutions (AOAC, Nordic Committee on Food Analysis, etc.) as well as numerous other laboratories have developed, verified, and/or successfully used classical dry ashing in practical analyses of a number of materials of biological origin. Hence, it is desirable to find out under which conditions the latter decomposition technique yields good and accurate results. Since electroanalytical techniques are among the most demanding with regard to the completeness of the biological matrix removal, we decided to critically review the literature published after 1978 in which classical dry ashing is combined with some version of electroanalytical measurement. It emerged from this review that in particular the charring step requires careful performing. When performed well, classical dry ashing leads to complete removal of the organic matrix and to accurate analytical results for a number of determined elements.

Immunomodulators isolated from microorganisms.

Microbial products are surveyed that have an immunoregulatory activity, both from the realm of low-molar-mass compounds and from the group of naturally occurring polymers. The data include in most cases the producer organism or source, a brief chemical characteristic and biological activity. Various groups of substances are compared, the drawbacks attendant on their acquisition and application are pointed out and their advantageous properties are specified.

The effect of inorganic phosphate on the production of avermectin in Streptomyces avermitilis.

The effect of phosphate on the production of avermectin B1a, growth and utilization of glucose in the course of cultivation of Streptomyces avermitilis on a complex and chemically defined medium has been studied. Phosphate added at the beginning of cultivation at 1-20 mmol/l did not distinctly affect the production of secondary metabolite. From the results it follows that the biosynthesis of avermectin tolerates high concentrations of phosphate in the medium.

Role of phosphatases in the biosynthesis of chlortetracycline in Streptomyces aureofaciens.

ATP diphosphohydrolase activity and inorganic pyrophosphatase reached two maxima during cultivation of the low- and high-producing variant of Streptomyces aureofaciens under conditions of phosphate limitation, i.e. after 30 and 70 h of cultivation. Increased levels of inorganic phosphate in a medium inhibitory to biosynthesis of chlortetracycline markedly decreased the levels of both enzymes. The ATP diphosphohydrolase activity was detected both in the supernatant and membrane fractions of the cell-free preparation of the mycelium.

Properties of apyrase and inorganic pyrophosphatase in Streptomyces aureofaciens.

Apyrase (ATP-diphosphohydrolase, EC 3.6.1.5) and inorganic pyrophosphatase (EC 3.6.1.1) were partially purified from S. aureofaciens RIA 57 and characterized. Apyrase degrades, in addition to ATP, other nucleoside triphosphates and nucleoside diphosphates, diphosphate, thiamine diphosphate, phosphoenolpyruvate and oligophosphates of chain length n less than 90. The apyrase activity was detected in the membrane and supernatant fractions. Its properties (substrate specificity. effect of inhibitors, pH optimum and effect of Mg2+ ions) were similar in both fractions except for the effect of oligomycin that inhibited only the membrane fraction. Pyrophosphatase exhibited a strict substrate specificity, substrates other than diphosphate being degraded relatively slowly. Of other enzymes exhibiting the phosphatase activity acid phosphatase (EC 3.1.3.2) and alkaline phosphatase (EC 3.1.3.1), trimetaphosphatase (EC 3.6.1.2) and exopolyphosphatase (EC 3.6.1.11) degrading oligophosphatase of chain length n = 15, 40 and 60, were detected.

[Action of chlortetracycline on the enzymes of the producer itself, Streptomyces aureofaciens]. / Deistvie khlortetratsiklina na énzimy sobstvennogo produtsenta Streptomyces aureofaciens.

When preparing a cell-free extract of Streptomyces aureofaciens from the culture to which chlortetracycline (1000 gamma/ml) was added before disintegration with alumina, a considerable decrease in the enzyme activity was reached. The presence of chlortetracycline during disintegration of the cells by means of glass beads did not substantially affect the enzyme activity of the cell-free extract. Addition of chlortetracycline directly to the reaction mixture for the enzyme assay (up to a concentration of 200 gamma/ml) did not induce any inhibition effect. The results suggested that during studying enzyme systems of organisms producing secondary metabolites, the product might distort the results on the use of an inconvenient method.

Regulation and biosynthesis of secondary metabolites. XVIII. Adenylate level and chlorotetracycline production in Streptomyces aureofaciens.

The relationship was studied between the energy metabolism of the actinomycete Streptomyces aureofaciens and the biosynthesis of chlorotetracycline by this organism. The energy charge values in a culture of low-production strain were almost identical with those of a production variant but the total sum of adenylates was about 10 times higher. In the stationary growth phase both strains evinced a drop in energy charge values followed by a rise to the original level. An increase in the concentration of inorganic phosphate in fermentation medium caused a suppression of antibiotic formation in the lowproduction strain and further rise in the total adenylate level. The expression of the energy charge in Streptomyces aureofaciens acquires a complex character owing to the participation, apart from the adenylate system, of high-molecular polyphosphates as energy donors and the probable lack of a regulating mechanism such as the adenylate kinase reaction.