Isolation and characterization of the stage-specific cytochrome b small subunit (CybS) of Ascaris suum complex II from the aerobic respiratory chain of larval mitochondria.
We recently reported that Ascaris suum mitochondria express stage-specific isoforms of complex II: the flavoprotein subunit and the small subunit of cytochrome b (CybS) of the larval complex II differ from those of adult enzyme, while two complex IIs share a common iron-sulfur cluster subunit (Ip). In the present study, A. suum larval complex II was highly purified to characterize the larval cytochrome b subunits in more detail. Peptide mass fingerprinting and N-terminal amino acid sequencing showed that the larval and adult cytochrome b (CybL) proteins are identical. In contrast, cDNA sequences revealed that the small subunit of larval cytochrome b (CybS(L)) is distinct from the adult CybS (CybS(A)). Furthermore, Northern analysis and immunoblotting showed stage-specific expression of CybS(L) and CybS(A) in larval and adult mitochondria, respectively. Enzymatic assays revealed that the ratio of rhodoquinol-fumarate reductase (RQFR) to succinate-ubiquinone reductase (SQR) activities and the K(m) values for quinones are almost identical for the adult and larval complex IIs, but that the fumarate reductase (FRD) activity is higher for the adult form than for the larval form. These results indicate that the adult and larval A. suum complex IIs have different properties than the complex II of the mammalian host and that the larval complex II is able to function as a RQFR. Such RQFR activity of the larval complex II would be essential for rapid adaptation to the dramatic change of oxygen availability during infection of the host.
Department of Biomedical Chemistry, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Hisako
H
Amino
Arihiro
A
Osanai
Hiroko
H
Miyadera
Noriko
N
Shinjyo
Eriko
E
Tomitsuka
Hikari
H
Taka
Reiko
R
Mineki
Kimie
K
Murayama
Shinzaburo
S
Takamiya
Takashi
T
Aoki
Hideto
H
Miyoshi
Kimitoshi
K
Sakamoto
Somei
S
Kojima
Kiyoshi
K
Kita
D000332:Aerobiosis; D000595:Amino Acid Sequence; D000818:Animals; D017165:Ascaris suum / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development*; D003001:Cloning, Molecular; D003573:Cytochrome b Group / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004579:Electron Transport; D007700:Kinetics; D007814:Larva / Q000201:enzymology; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D010449:Peptide Mapping; D010802:Phylogeny; D016415:Sequence Alignment; D013045:Species Specificity
D003573:Cytochrome b Group; D009097:Multienzyme Complexes