ASSEMBLY OF ALCOHOL OXIDASE IN PEROXISOMES OF THE YEAST HANSENULA-POLYMORPHA REQUIRES THE COFACTOR FLAVIN ADENINE-DINUCLEOTIDE

The peroxisomal flavoprotein alcohol oxidase (AO) is an octamer (600 k Da) consisting of eight identical subunits, each of which contains one flavin adenine dinucleotide molecule as a cofactor. Studies on a ribo flavin (Rf) auxotrophic mutant of the yeast Hansenula polymorpha revea led that limitation of the cofactor led to drastic effects on AO impor t and assembly as well as peroxisome proliferation. Compared to wild-t ype control cells Rf-limitation led to 1) reduced levels of AO protein , 2) reduced levels of correctly assembled and activated AO inside per oxisomes, 3) a partial inhibition of peroxisomal protein import, leadi ng to the accumulation of precursors of matrix proteins in the cytosol , and 4) a significant increase in peroxisome number. We argue that th e inhibition of import may result from the saturation of a peroxisomal molecular chaperone under conditions that normal assembly of a major matrix protein inside the target organelle is prevented.