SYNTHESIS OF HOLO PARACOCCUS-DENITRIFICANS CYTOCHROME C(550) REQUIRESTARGETING TO THE PERIPLASM WHEREAS THAT OF HOLO HYDROGENOBACTER-THERMOPHILUS CYTOCHROME C(552) DOES NOT - IMPLICATIONS FOR C-TYPE CYTOCHROME BIOGENESIS

Expression from a plasmid of the complete gene, including the codons f or the N-terminal periplasmic targeting signal, for cytochrome c(550) of Paracoccus dentrificans led to the formation of the hole protein in the periplasms of both P. dentrificans and Escherichia coli. Expressi on of the gene from which the region coding for the targeting signal h ad been specifically deleted resulted in formation of ape-protein in t he cytoplasms of both organisms. These findings are consistent with ha em attachment occurring in the periplasm. In contrast, the formation o f holo cytochrome c(552) from Hydrogenobacter thermophilus following e xpression of the gene lacking the periplasmic targeting sequence in ei ther P. denitrificans or E. coli is attributed to spontaneous cytoplas mic attachment of haem to the thermostable protein.