STRUCTURAL AND FUNCTIONAL-ASPECTS OF PEROXISOMAL MEMBRANES IN YEASTS

The peroxisomal membrane compartmentalizes specific metabolic function s in the intermediary metabolism of various aerobic eukarya. In yeast, peroxisomal membranes are typified by their small width (+/- 7-8 nm) and absence of large integral membrane proteins in freeze-etch replica s. They show a unique polypeptide profile which, in contrast to their phospholipid composition, differs from that of other membranes in the cell. Part of these proteins are substrate-inducible and are probably related to specific peroxisomal function(s). In vivo, the observed pro ton motive force across the peroxisomal membrane may play a role in th e function of the organelle in that it contributes to the driving forc e required for selective transport of various enzyme substrates and/or metabolic intermediates. To date only few peroxisomal membrane protei ns (PMPs) have been functionally characterized. A major constitutive 3 1-kDa PMP present in the peroxisomal membrane of Hansenula polymorpha has been purified and was shown to display pore-forming properties. In addition, a peroxisomal H+-ATPase has been identified which most prob ably is involved in the generation/maintenance of the in vivo pH gradi ent across the peroxisomal membrane. Other functions of peroxisomal me mbrane proteins remain obscure although the first genes encoding yeast PMPs are now being cloned and sequenced. Studies on peroxisome-defici ent yeast mutants revealed that specific peroxisome functions are stri ctly dependent on the intactness of the peroxisomal membrane. In this contribution several examples are presented of metabolic disorders due to peroxisomal malfunction in yeast.