The Rate of Endogenous Respiration as Affected by the Oxidation of Exogenous Substrates

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Abstract
The release of C14O2 was compared with O2 uptake of minced vegetative cells of Penicillium chrysogenum Q176 previously grown for 6 hrs. in a medium containing carboxy- and methyl-labeled acetate. Oxidation of glucose did not affect the rate of production of C14O2 while oxidation of acetate eventually suppressed the C14O2 release almost completely. Even though the endogenous RQ (0774) was relatively uniform over a 4-hr. period, the C14O2/O2 ratio became constant only during the 2d half of the expt. In cells previously starved then grown in labeled acetate for 2 hrs., over 50% of C14O2 was released during the first 30 min. of a 3-hr. expt. Thus, according to the authors, only if all cellular components have the same specific activity should detn. of C14O2 evolution allow a realistic estimate of the total endogenous respiration, and even then not all kinetic (which is preferable to single detn.) data can be interpreted unequivocally.
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