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 ferrit in into adult Geotria australis over 10 weeks, resulted in a progressi ve increase in that form of iron in the serum. However, as with contro l animals, the ferritin in the liver of injected lampreys consisted of one subunit type, whose M(r) (20300) differed from those of the two s ubunit types of horse spleen ferritin. Thus, lampreys had converted ho rse 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 b y pronounced increases in superoxide dismutase (SOD) activity. This ri se, which parallels the rise in SOD activity that occurs as iron incre ases during the very protracted upstream migration of G. australis, is consistent with the view that SOD protects against iron-mediated dama ge by removing the superoxide radical, which facilitates the formation of the highly toxic hydroxyl radical. A levelling off of the iron con centration between weeks 2 and 8 was accompanied by a decline in SOD a ctivity, even though nonhaem iron levels were well above those of cont rol 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.