Screening of yeasts producing stable L-lactate cytochrome c oxidoreductase and study of the regulation of enzyme synthesis

Screening of strains producing a stable form of L-lactate cytochrome c oxidoreductase (flavocytochrome b ₂, FC b ₂) was carried out among 14 yeast species. Enzyme activity was detected in polyacrylamide gel after the electrophoresis of cell-free extracts. The FC b ₂ of Hansenula polymorpha, Rhodotorula pilimanae, and Kluyveromyces lactis are characterized by high thermostability; in particular, the FC b ₂ of H. polymorpha retains its activity and tetrameric structure even after heating at 60°C for 10 min. Constitutive synthesis of FC b ₂ was observed in H. polymorpha grown on either glucose, ethanol, or glycerol. L-Lactate induces de novo synthesis of FC b ₂, as proved by the use of cycloheximide, an inhibitor of protein synthesis.