MUCOSAL SURFACE FERRICYANIDE REDUCTASE-ACTIVITY IN MOUSE DUODENUM

Mouse duodenum possesses mucosal surface ferricyanide reductase activi ty, The reducing activity, determined ill vitro by measuring ferrocyan ide production from ferricyanide, was found to be greater in duodenal fragments when compared with ileal fragments, Experiments with right-s ide out tied-off duodenal sacs show that reduction occurs mainly on th e mucosal side and indicates that the reducing activity is associated with the brush border membrane, Experiments using mice with increased levels of iron absorption (hypoxic, iron-deficient) showed correspondi ng increases in reducing activity, The increase was present in duodena l but not ileal fragments, Inhibitor studies showed no effect of sever al compounds which inhibit other, more characterized, transplasma memb rane reductases. In particular, doxorubicin (10 mu M) and quinacrine ( 1 mM) were without effect on duodenal mucosal transplasma membrane red ucing activity, Depolarization of the membrane potential with high med ium K+ inhibited reducing activity, N-ethyl malemide (1 mM) was a pote nt inhibitor, but iodoacetate was found to be less inhibitory, Compari sion with inhibitory effects on glyceraldehyde-3-phosphate dehydrogena se (GAPDH) demonstrated that the effect of N-ethyl malemide on reducin g activity was not secondary to GAPDH, Collectively these results indi cate that mouse duodenum possesses mucosal surface transplasma membran e ferricyanide reductase activity and that the activity is correlated with the process of intestinal iron absorption, Furthermore, the reduc ing activity appears to be distinct from other reported transplasma me mbrane reductases.