Properties and regulation of a trans-plasma membrane redox system in XXXX liver.

@entity2125 @entity26 @entity653 @entity12039 @entity1919 @entity880 @entity35 @entity9588 @entity1068 @entity413 @entity71254
1. Regulation of the reduction of @entity9588 by the isolated perfused @entity35 liver was studied. 2. The rate of reduction was dependent on the rate of supply of @entity9588 and independent of perfusate @entity26 concentration. 3. The effect of pH was also examined; the rate of reduction was optimal at pH 7.4 and was inhibited to a greater extent by pH values below 7.4 than those above 7.4. 4. The effects of substrates on the rate of @entity9588 reduction was assessed. Reductants of the cytosolic and mitochondrial @entity2125 / @entity2125 couple were tested. @entity71254 (10mm), @entity880 (10mm), @entity653 (10mm) and @entity1068 (10mm) each had no effect. @entity12039 (10mm) stimulated the rate. 5. Dehydroascorbate (1mm), stimulated the rate of @entity9588 reduction; the stimulation did not appear to be attributable to the production of reduced substances that were excreted to reduce extracellular @entity9588 . 6. The effects of glucagon and @entity1919 on the rate of @entity9588 reduction were examined. Glucagon inhibited the rate by approx. 30% and half-maximal inhibition occurred at 0.1 nm, corresponding to the concentration at which half-maximal stimulation of @entity413 release occurred. @entity1919 stimulated @entity413 release but had no significant effect on the rate of @entity9588 reduction. It is concluded that the trans-plasma membrane redox system of liver that reduces extracellular @entity9588 is regulated by glucagon. The rate is also altered by the substrate @entity12039 . The effect of glucagon may be direct as it cannot be mimicked by @entity1919 and it occurs directly following exposure to the hormone.
