Adriamycin as an inhibitor of 11 beta-hydroxylase activity in adrenal cortex mitochondria

Inhibition of 11 beta-hydroxylase activity was observed to be due to the interaction of adriamycin with adrenal cortex mitochondria. The inhibition of the enzyme was uncompetitive, with an apparent Ki of 100 microM, and was dependent upon the concentration of the drug and the time of incubation. Adriamycin increased the oxygen consumption of these mitochondria. EPR studies showed that adriamycin was reduced to a free radical semiquinone which served to shuttle electrons to oxygen, leading to an impairment in the reduction of cytochrome P450. It is suggested this may be the mechanism for the inhibitory effect of the drug on 11 beta-hydroxylase activity.     

A rubredoxin-like mononuclear FeS4 derivative of adrenal iron-sulfur protein (adrenodoxin)

A rubredoxin-like mononuclear iron-sulfur derivative of adrenodoxin was prepared from the apoprotein and FeCl₃ in the presence of dithiothreitol. The mononuclear compound displayed optical absorption maxima at 276, 350, and 500 nm, and exhibited electron paramagnetic resonance absorption at g = 4.27 with a shoulder at g = 4.28, which can be ascribed to high spin ferric ion. From p-chloromercuriphenyl sulfonate titration experiments the iron atom appears to contain approximately one g atom of iron per mole of protein. This rubredoxin-like derivative was very unstable at 22° (the half-life was approximately 10 minutes), whereas the native 2 Fe2S1 protein is known to be quite stable. This instability is believed to be intrinsic to the polypeptide sequence of adrenodoxin.     

Sulfhydryl groups are involved in H+ translocation via the uncoupling protein of brown adipose tissue mitochondria

Mersalyl inhibits H+ transport via the uncoupling protein (UP) in brown adipose tissue (BAT) mitochondria estimated as swelling in potassium acetate (Ki 67 microM) or as valinomycin-induced H+ extrusion in K2SO4 (Ki 55 microM) and KCl. The swelling in KCl is depressed only slightly. Some other SH-reagents (p-hydroxymercuribenzoate, 5,5'-dithiobis(2-nitrobenzoate) and thiolyte DB), but not hydrophobic reagents (N-ethylmaleimide and eosin-5-maleimide), exhibit analogous inhibition. Thus an essential SH-group localized at the water-accessible cytosolic surface of UP was found to be involved in H+ transport via UP but not in Cl- transport.