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PubMed1979

Iron-bleomycin interactions with oxygen and oxygen analogues. Effects on spectra and drug activity.

Despite extensive structural dissimilarities, iron . bleomycin complexes and heme-containing oxygenases display remarkable similarities in binding oxygen antagonists and in spectral properties deriving from bound iron. Fe(II)-bleomycin reversibly forms a complex with either CO or isocyanide (lambda max = 384 and 497 nm, respectively), either of which interfere with its oxygen-dependent cleavage of DNA. A similar but paramagnetic complex forms with NO (lambda max = 470 nm; AN = 24 G). In contrast, cyanide enhances bleomycin activity against DNA. Complexes of bleomycin and FE(III), formed either by direct association or by autoxidation of the Fe(II) . bleomycin complex, exhibit indistinguishable EPR and visible spectra, which change characteristically with pH. At neutral pH, Fe(III) . bleomycin is a low spin complex (g = 2.45, 2.18, 1.89; lambda max = 365, 384 nm) and, at low pH, it is a high spin rhombic complex (geff = 9.4, 4.3; lambda max = 430 nm). These complexes are interconvertible (pK 4.3). Fe(II) . bleomycin oxidation, although reversible by spectral criteria, is accompanied by drug inactivation unless DNA is present.

Animals↗
PubMed1979

Effect of high concentrations of nitrogen on mixed populations of nitrifying bacteria isolated from industrial nitrogenous wastewaters.

The effect of high concentrations of different forms of nitrogen (NH4+, NO2-, NO3- and urea N) on nitrification by mixed populations of nitrosobacters isolated from nitrogen fertilizer plant wastewaters and nitrobacters isolated from effluents from a biological bed treating these wastewaters was determined. The inhibitory activity (within the concentration values for industrial wastewaters) of only the reaction products was observed, i.e. nitrites for nitrification phase I and nitrates for nitrification phase II. A mixed population of phase II nitrifying bacteria is highly resistant to high concentrations of ammonia nitrogen (50% inhibition at 3,000 mg N/l).

Ammonia↗
PubMed1979

Electron spin resonance studies on phaeomelanins.

ESR spectra of synthetic melanins formed from dopa and from 5-S-cysteinyldopa and of melanins isolated from human melanomas were studied. Alkali-soluble melanin synthesized from cysteinyldopa showed a signal similar to that of insoluble melanin synthesized from dopa, but also a simple fine structure. Trichochromes C and F synthesized from 5-S-cysteinyldopa had a broader signal than dopamelanin, and in addition a hyperfine structure that could be explained by the presence of manganous ions. An insoluble eumelanin from a human melanoma with a sulphur content of 5% showed an ESR spectrum consisting of one line like dopamelanin. An alkali-soluble phaeomelanin from a human melanoma with a sulphur content of 10% showed a very broad signal with a hyperfine structure that could be explained by the presence of manganous ions.

Chemical Phenomena↗
PubMedDate not supplied

[Changes in the physiologic properties of a chemostat culture of Propionibacterium shermanii during growth limitation by a deficiency of sodium lactate].

A chemostat curve has been constructed for changes in the Propionibacterium shermanii population density with an increase in the flow rate of the medium from 0.04 to 0.55 h-1 upon limitation of the growth with sodium lactate deficiency. The curve differs from the classic chemostat curve described with the Monod equation, thus indicating changes in metabolism at different growth rates. Fermentation of lactate to acetic and propionic acids by the culture is most complete at low flow rates of the medium (D = 0.04 h-1). The rates of oxidation processes increase at average flow rates (D = 0.1--0.33 h-1). Lactate is both fermented to yield volatile acids, and oxidized. The growth rate D = mu = 0.55 h-1 approaches the maximal one. The rate of fermentation by the culture at this growth rate decreases while the rate of oxidation increases. The ratio between the rates of these two processes shifts towards oxidation. The cells display now a very high synthetic activity: constructive metabolism of the cells is realized practically only at the account of the nitrogen from ammonium rather than the nitrogen of amino acids. The chemical composition of the cells along the chemostat curve is relatively constant. The content of protein and DNA does not change; the content of RNA slightly rises with an increase in the growth rate, and the protein synthesizing activity of RNA is directly proportional to D = mu.

Bacterial Proteins↗
PubMed1976

Oxidation of p-cresol by horseradish peroxidase compound I.

Rate constants for the reaction between horseradish peroxidase compound I and p-cresol have been determined at several values of pH between 2.98 and 10.81. These rate constants were used to construct a log (rate) versus pH profile from which it is readily seen that the most reactive form of the enzyme is its most basic form within this pH range so that base catalysis is occurring. At the maximum rate a second order rate constant of (5.1 +/- 0.3) x 10(-7) M-1 s-1 at 25 degrees is obtained. The activation energy of the reaction at the maximum rate was determined from an Arrhenius plot to be 5.0 +/- 0.5 kcal/mol. Evidence for an exception to the generally accepted enzymatic cycle of horseradish peroxidase is presented. One-half molar equivalent of p-cresol can convert compound I quantitatively to compound II at high pH, whereas usually this step requires 1 molar equivalent of reductant. The stoichiometry of this reaction is pH-dependent.

Cresols↗