Abstract
Summary
Cell suspensions and homogenates of Tetrahymena pyriformis contain dehydrogenases which reduce triphenyltetrazolium chloride in anaerobiosis to formazan in the presence of some purine substrates (guanine, iso-guanine, hypoxanthine, xanthine). The dehydrogenase activity was also revealed in oxygen consumption experiments using methylene blue as hydrogen acceptor. Homogenates of Tetrahymena oxidized purine substrates in the air only weakly and were shown to be devoid of uricase activity. Guanine in lower concentration corresponding to the amount required for growth stimulated slightly the respiration of washed cells, but higher concentrations inhibited markedly the O2 consumption. The instability of purine dehydrogenases and inequality between oxidase and dehydrogenase activities may account for some discrepancies in the literature.
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