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Apo forms of cytochrome C 550 and cytochrome cd 1 are translocated to the periplasm of Paracoccus denitrificans in the absence of haem incorporation caused by either mutation or inhibition of haem synthesis
Author(s) -
Page M. D.,
Ferguson S. J.
Publication year - 1990
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1990.tb00693.x
Subject(s) - periplasmic space , paracoccus denitrificans , biology , biochemistry , cytochrome , mutant , cytochrome c , heme , microbiology and biotechnology , enzyme , gene , escherichia coli , mitochondrion
Summary An apo form of cytochrome C 550 can be detected by immunoblotting cell‐free extracts of a mutant of Paracoccus denitrificans that is deficient in c ‐type cytochromes. This apoprotein is found predominantly in the periplasm, the location of the holocytochrome in the wild‐type organism, indicating that translocation of the polypeptide occurs in the absence of haem attachment. The polypeptide molecular weight, as judged by sodium dodecyl sulphate/polyacrylamide gel electrophoresis, is indistinguishable from that of the holoprotein and the chemically prepared apoprotein; this suggests that the N ‐terminal signal sequence is removed in the mutant as in the wild‐type organism. In the presence of levulinic acid, an inhibitor of haem biosynthesis, apocytochrome c 550 and aponitrite reductase (cytochrome cd 1 ) accumulated in the periplasm of wild‐type cells. Synthesis of these apoproteins was blocked by chloramphenicol. Thus in P. denitrificans the synthesis of these polypeptides is neither autoregulated nor regulated by the availability of haem. That the apoproteins appear in the periplasm argues against the possibility of polypeptide/haem co‐transport from cytoplasm to periplasm. These observations are related to, and contrasted with, the biosynthesis of c ‐type cytochromes in eukaryotic cells.