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PubMed1956

The effect of temperature on oxidative phosphorylation with insect flight muscle mitochondria.

The effect of different temperatures on the biochemical activity and morphology of insect flight muscle mitochondria was examined. It was found that respiration and phosphorylation have the same thermal response at temperatures of 25 degrees C. and below. The energy of activation for both systems is approximately 12,300 calories. Oxidation and phosphorylation can be uncoupled effectively by temperature, for at temperatures above 25 degrees C. there is more rapid heat inactivation of phosphorylation. This is evident from reduced P/O values as well as from morphological deterioration in the mitochondrial population. The thermal response of both this sarcosomal enzyme system and the respiration in the living fly are quantitatively similar.

Cell Respiration↗
PubMed1956

Factors affecting the production of chromosome aberrations by chemicals.

In the present paper, the results of a study on the influence of temperature, hydrogen ion concentration, and oxygen tension on the production of chromosome aberrations in Vicia root tips by maleic hydrazide (MH), di-(2, 3-epoxypropyl)ether (DEPE), and 8-ethoxycaffeine (EOC), are described. Variations in the hydrogen ion concentration of the treatment solutions did not significantly influence the effect of EOC and DEPE. In contrast, the MH effect was considerably diminished by raising the pH from 4.7 to 7.3. A marked increase in the frequencies of aberrations produced by DEPE and MH was obtained by raising the temperature from 3 degrees to 25 degrees C. The effect of EOC increased with rising temperature up to 12 degrees C. With a further rise in temperature the effect of EOC decreased, so that at 25 degrees C. it was of about the same magnitude as at 3 degrees C. The effect of EOC was completely inhibited, and that of MH partly so, when during the treatment (1) oxygen was excluded from the solution, (2) respiration was inhibited by azide or cyanide, or (3) phosphorylation was uncoupled from respiration by 2, 4-dinitrophenol (DNP). Pretreatments with DNP had a similar effect, but posttreatments did not influence the frequencies of aberrations. The effect of DEPE was unchanged by anoxia. Pre- or posttreatments with DNP did not change the total number of aberrations produced by DEPE, but the appearance of the effect was considerably delayed. The results are discussed.

Caffeine↗
PubMed1956

The properdin system and immunity. V. The bactericidal activity of the properdin system.

Methods for the preparation and standardization of reagents suitable for studies on the bactericidal action of the properdin system are described. The preparation and properties of serum free of properdin (RP(b)) are presented in detail because of the necessity for a suitable RP(b) in these studies. The properdin system is responsible for the bactericidal action of normal human serum against a variety of microorganisms. The present work shows that the removal of properdin from serum also removes bactericidal activity. Addition of properdin to properdin-deficient serum restores bactericidal activity. A quantitative relationship exists between the final properdin concentration and bactericidal activity against sensitive organisms. The possibilities of a bactericidal assay for properdin are discussed. It is demonstrated that, in addition to properdin, the four components of complement (present in RP(b)) are necessary for the destruction of properdinsensitive bacteria. If any component is missing, bactericidal activity is lost; when the component is replaced, bactericidal activity is restored. Magnesium is also necessary for the bactericidal activity of the properdin system. Maximal bactericidal activity is obtained with magnesium concentrations similar to that of normal human serum (10(-3) to 10(-4)M). The bactericidal activity of the properdin system occurs only at temperatures above 15 degrees . Resistant strains have been encountered in species of bacteria sensitive to the properdin system. Resistance or sensitivity is a characteristic of the individual strain and not of the species. The widespread occurrence of the properdin system in normal mammalian serum and the variety of bacteria destroyed by it suggest that the properdin system is a factor in natural resistance.

Animals↗