Growth inhibition without ATP decrease in Rhodotorula gracilis coltured under reduced oxygen pressure

In Rhodotorula gracilis ccultured in liquid medium, growth (as protein accumulation) is progressively inhibited when pO2 is lowered from 3 mm Hg (in the liquid medium) to zero. Half-maximum growth is observed at a pO2 value of 2 mm Hg. Under this condition the rate of incorporation of labelled leucine into protein is about halved. The inhibition of leucine incorporatedn below pO2 is almost immediate and remains quantitavively unchanged for almost 30 min after the shift. In contrast, no changes in the ATP, ADP and AMP levels are observed during the shift and in following 10 min; only in the period from 10 to 45 min after the shift ADP and AMP progressive y increase. These results are interpreted as indicating that the inhibition of protein synthesis and growth by O2 shortage under the experimental condition investigated does not depend on changes in the phosphorylation state of the adenosine phosphate syttem, thus suggesting that some other system able to react to pO2 changes is involved in the response of the biosynthesis processes to O2 deficiency.