'- H
                   1,2-propanediol
                                  . W 4                             S-CoA
                                                            Spropionyl-CoA
                                                                     phosphotransacylase?

         O PduC
         O PduD                                                 propionyl-phosphate
         ) PduE                                                              ADP
         O PduG o PduH
         * PduO                                                              ATP



       Diol dehydratase                                      NA      propionate
  ,    Diol dehydratase                               N
       reactivating factor                                 PduQ             OH
                                                           PduQ
                                            propionaldehyde            propanol

Figure 4-8. A model of thepdu organelle. The dashed line indicates the shell of the
           organelle which is composed of the PduA protein and perhaps the
           PduBB'JKTU as well. The enzymes of the organelle are graphically
           represented and are indicated in the legend. However, their placement in the
           organelle has not been determined experimentally. The pathway of PD
           degradation is also shown. It is proposed that PD enters the organelle where it
           is converted to propionaldehyde by the PduCDE diol dehydratase. The propionaldehyde is channeled to the PduP aldehyde dehydrogenase and
           converted to propionyl-CoA which diffuses out of the organelle and is
           converted to propionate with the production of ATP. Part of the aldehyde is
           oxidized to propionyl-CoA as it diffuses out of the organelle and part is
           reduced to propanol outside of the organelle. Further conversion of
           propionyl-CoA occurs outside of the organelle. Propionaldehyde which
           escapes channeling is sequestered within the organelle to protect cytoplasmic
           cellular components. However, some propionaldehyde escapes into the
           cytoplasm where it is converted into 1-propanol. The putative alcohol
           dehydrogenase (PduQ), propionate kinase (PduW), and phosphotransacylase, were not detected in the organelles purified for this study, and here are shown
           as part of the PD degradation pathway that occurs outside of the polyhedra.