Utilization by Yeast of d‐Lactate and l‐Lactate as Sources of Energy in the Presence of Antimycin A

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Abstract
Saccharomyces cerevisiae cells contain d and l‐lactate: cytochrome c oxidoreductases. The physiological role of these enzymes is investigated by inhibiting the respiratory chain with antimycin A and observing how the vital functions (respiration, protein biosynthesis, growth) are altered. When d or l‐lactate are provided as the source of energy, stoichiometric amounts of the antibiotic decrease the growth rate about five‐fold, the oxygen uptake two‐fold and the energetic efficiency eleven‐fold.In the presence of antimycin A, it was often proposed that only a very short chain consisting of one of the lactate dehydrogenases, cytochrome c and cytochrome oxidase could be involved in the oxidation of lactate. Consistent with this scheme are the measurements of lactate and oxygen uptake and the observation that keto acids are released into the external medium, which also allow one to rationalize the growth yield and the amino acid incorporation results.