Constitutive expression of phosphoketolase, a key enzyme for metabolic shift from homo- to heterolactic fermentation in QU 25.

Phosphoketolase (PK) is responsible for heterolactic fermentation; however, the PK gene of QU 25, , is transcribed constitutively, even under homolactic fermentation conditions. In order to deduce the regulatory mechanisms of PK activity in QU 25, XfpA levels in QU 25 cells under hetero- and homolactic fermentation conditions were tested using western blotting. The results showed that the XfpA protein expression was similar under both conditions and that the expression products formed complexes, most likely homodimers, indicating that the regulation of PK activity is downstream of translation.