SUMMARY: Maximum molar growth yields on oxygen ( and succinate ( ) were not affected when carbon-limited NCIB 8250 was changed to oxygen limitation. →H+/O quotients for cells grown with succinate- or ammonium-limitation did not differ significantly from those obtained with oxygen-limited cells. The levels of cytochromes and remained constant at 0·13 and 0·05 nmol (mg protein) respectively in crude cell-free extracts of succinate-limited organisms grown at high (80mmHg) or low (5-10 mmHg) dissolved oxygen tension respectively. Their levels increased in oxygen-limited conditions, when cytochrome a () was additionally synthesized and organisms exhibited increased resistance to cyanide inhibition of respiration. It is concluded that the respiratory efficiency of NCIB 8250 is unaffected by oxygen concentration under the conditions studied. Theoretical calculations are presented for maximum molar growth yields on succinate and oxygen and these are compared with experimental values. Although the effective P/O ratio is only about unity, energy is probably conserved at two sites of oxidative phosphorylation and this is independent of the synthesis of cytochrome () under conditions of oxygen limitation. Possible reasons for the observed low molar growth yields are discussed.


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