ELECTRON-TRANSPORT COMPONENTS OF THE PARASITIC PROTOZOAN GIARDIA-LAMBLIA

The energy metabolism of the intestinal parasite, Giardia lamblia, inv olves the iron-sulphur protein, pyruvate:ferredoxin oxidoreductase. Ce ll fractionation studies showed that this enzyme is associated with th e membranes. NADH and NADPH dehydrogenases were found in both the memb rane and cytosolic fractions. EPR spectroscopic studies showed the pre sence of iron-sulphur clusters in the membrane fraction and in the cyt osolic fraction, non-sedimentable at 6 x 10(6) g.min. An acidic, solub le protein fraction was separated from the cytosol. It had an EPR spec trum in the reduced state, characteristic of the 2[4Fe-4S] type of fer redoxin, with g-factors at 2.04, 1.93 and 1.89, and the midpoint redox potential was estimated to be -360 mV. This species is probably a fer redoxin, like those of anaerobic bacteria such as Clostridium and Desu lfovibrio spp. and also that of Entamoeba histolytica. The protein was readily and irreversibly oxidized to give [3Fe-4S] clusters.