Evidence for an unusual mechanism of membrane translocation of the periplasmic hydrogenase ofDesulfovibrio vulgaris(Hildenborough), as derived from expression inEscherichia coli

Using a subcellular fraction procedure, the location in the cell has been studied of the recombinant hydrogenase as expressed by an Escherichia coli clone carrying the structural genes for both the subunits of the Desulfovibrio vulgaris enzyme. In D. vulgaris the enzyme was extracted with the periplasmic fraction. However, when expressed in E. coli, only a minor portion of the recombinant enzyme co-fractionated with the periplasm: the majority of the larger subunit was detected in the cytoplasmic fraction in E. coli, while most of the smaller subunit was found, in precursor form, in the membrane fraction. In E. coli clones in which the gene for either one of the subunits had been deleted, the export of the other subunit was completely abolished. These observations indicate that a special mechanism, which functions only poorly in E. coli, is involved in translocation of the enzyme across the inner membrane. Some factors of potential relevance for this poor transtranslocation; in E. coli are discussed.