Molecular regulation of methanol oxidase activity in continuous cultures of Hansenula polymorpha

Abstract The regulation of methanol oxidase (MOX) in Hansenula polymorpha has been studied in continuous cultures using a mixture of glucose and methanol (4:1 w/w) as carbon source. The study focused on the identification of stages in the biosynthesis affecting the formation of active MOX in glucose‐methanol‐grown cells. The levels of MOX mRNA, MOX protein in monomeric and octameric from, the ratio FAD/MOX, and the actual MOX activity have been quantified as functions of the dilution rate D . Hybridization studies with MOX mRNA probes showed an induction of MOX mRNA formation up to D = 0.29 h −1 . The induction of MOX protein synthesis (up to 37% of the cellular protein) is determined at low D values on the transcriptional level. The MOX activity at high D values is tuned by FAD incorporation and (post‐) translation. Despite the high levels of MOX mRNA, decreasing levels of MOX activity and MOX protein were found at D values ranging from 0.14 t 0.29 h −1 . The maximal ratio FAD/MOX(6) was determined at D = 0.1 h −1 , which correlated with the maximal specific activity of MOX. In glucose‐methanol media both protein level and MOX activity are repressed by increasing levels of residual glucose at high D values.