The absorption spectrum of intact cels ofRhodotorula mucilaginosaexhibits three absorption peaks for carotenoids and a Soret band for cytochrome(s). The difference spectrum between the reduced and oxidized states indicates there are components of cytochromeb,c(c1)anda+a3. However, the respiratory aspect of this strain differs significantly from that of baker's yeast,Saccharomyces cerevisiae. The respiratory capacity is strikingly enhanced in the transition from the lag to the logarithmic phase of growth, and is accompanied with a special increase in cytochrome oxidase. Addition of TMPD (plus ascorbate) in the presence of glucose barely affects oxygen consumption of the cells during this period, whereas it markedly affects consumption in older cells. Sodium azide slightly inhibits respiration in the course of growth, except during this limited transitional period. Azide-insensitive respiration is also seen in the mitochondrial fraction prepared from cells grown to the stationary state. A similar situation is found with antimycin A.Morphological investigations were carried out electron-microscopically on the cells of different growth stages.
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