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HOQNO interaction with cytochrome b in succinate:menaquinone oxidoreductase from Bacillus subtilis
Author(s) -
Smirnova Irina A.,
Hägerhäll Cecilia,
Konstantinov Alexandre A.,
Hederstedt Lars
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(94)01442-4
Subject(s) - oxidoreductase , chemistry , heme , stereochemistry , reductase , bacillus subtilis , cytochrome , quinone , enzyme , biochemistry , biology , bacteria , genetics
2‐ n ‐Heptyl4‐hydroxyquinoline‐ N ‐oxide (HOQNO) inhibits the succinate:quinone oxidoreductase activity of isolated and membrane‐bound succinate:menaquinone oxidoreductase of B. subtilis . The inhibition pattern resembles closely that observed for α‐thenoyltrifluoroacetone and carboxins in the mitochondrial succinate:ubiquinone oxidoreductase: ca. 90% of the activity is highly sensitive to HOQNO ( K i ca. 0.2 μM for the isolated enzyme) whereas the rest 10% proves to be resistant to the inhibitor. HOQNO binding is shown to perturb the absorption spectrum of the ferrous di‐heme cytochrome b of the B. subtilis succinate:quinone oxidoreductase both in the α and Soret bands. In addition, the inhibitor is shown to bring about a negative shift of E m of the low‐potential heme b . It is suggested that HOQNO interacts with a menasemiquinone binding site near the low‐potential heme and suppresses the MQ .− ‐to‐MQH 2 step of the quinone reductase reaction but allows partly for the MQ‐to‐MQ .− transition to occur; dismutation of MQ . formed in the latter reaction to MQ and MQH 2 may account for the 10% of the enzyme activity insensitive to HOQNO.