Hepatic molecular conversion and detoxification of ferritin iron in adult lampreys (Geotria australis), following natural and induced iron loading.

Weekly intramuscular injections of 3 mg of iron as horse spleen ferritin into adult Geotria australis over 10 weeks, resulted in a progressive increase in that form of iron in the serum. However, as with control animals, the ferritin in the liver of injected lampreys consisted of one subunit type, whose M(r) (20,300) differed from those of the two subunit types of horse spleen ferritin. Thus, lampreys had converted horse spleen ferritin iron into endogenous ferritin iron, presumably in their liver. Marked rises in hepatic non-haem iron during the first 2 weeks and between weeks 8 and 10 of iron injections were accompanied by pronounced increases in superoxide dismutase (SOD) activity. This rise, which parallels the rise in SOD activity that occurs as iron increases during the very protracted upstream migration of G. australis, is consistent with the view that SOD protects against iron-mediated damage by removing the superoxide radical, which facilitates the formation of the highly toxic hydroxyl radical. A levelling off of the iron concentration between weeks 2 and 8 was accompanied by a decline in SOD activity, even though nonhaem iron levels were well above those of control animals. Enhanced SOD activity may therefore only be required when there is an elevated flux of iron in the liver through low-molecular-mass intermediates. A small amount of ferritin iron was converted into the more inert haemosiderin iron.