Action de l'antimycine A sur la respiration et la structure des mitochondries d'Euglena gracilis Z

Induction by antimycin A of cyanide-resistant respiration in heterotrophic Euglena gracilis: Effects of growth, respiration and protein biosynthesis

The addition of antimycin A during the logarithmic phase of growth of heterotrophic Euglena gracilis cultures (in lactate or glucose medium) was immediately followed by decreased respiration and a cessation of grwoth. Induced cyanideresistent respiration appeared 5 h after the addition of the inhibitor then the cells started to grow again and could be cultured in the presence of antimycin A. Thus the cells exhibited a cyanide-and antimycin-resistant respiration which was, in addition, sensitive to salicylhydroxamic acid and propylgallate. Antimycin-adapted Euglena and control cells were compared for their biomass production and protein synthesis. The difference in growth yield between control and antimycin-adapted cells was not as high as would be expected if only the first phosphorylation site of the normal respiratory chain was active in the presence of antimycin A. Furthermore, the ability to incorporate labelled valine into proteins, under resting-cell conditions, was not changed. Strong correlations were established between the effects of respiratory effectors on O2 consumption and valine incorporation. These results suggest that sufficient energy for protein synthesis and growth is provided by the operation of the cyanide-resistant respiratory pathway in antimycin-adapted Euglena.

[Low temperature spectral study on Euglena gracilis Z during synchronous culture on lactate medium: Variation of cytochrome 556 content]

Low temperature spectra are described for whole Euglena cells. Euglena growing in synchronous culture with lactate medium show a cyclic variation of cytochrome 556 content during each cellular generation. The greatest quantity of cytochrome 556 seems to coincide with the non-dividing phase of the cells, the phase in which the mitochondrial network is observed. On the other hand after treatment of the Euglena with antimycin A, a correlation exists between the formation of giant mitochondria and an increase in the quantity of cytochrome 556.These results demonstrate the existence of a cyclic variation of cytochrome 556 synthesis in Euglena during synchronous growth on lactate medium.