Iron levels and major iron binding proteins in the plasma of ammocoetes and adults of the southern hemisphere lamprey Geotria australis Gray.

1. The major plasma iron binding proteins (IBP) of both larval and adult Geotria australis differ from those of other vertebrates. 2. Larval IBP has a M.W. of approximately 354,000 and is composed of 20 subunits of equal M.W. 3. Adult IBP is a tetramer (M.W. = c. 296,000) which readily dissociates into subunits of approximately 78,000. 4. Confirmation that plasma iron binding proteins were similar to ferritin in larvae and transferrin in adults was provided by pI values, Fe/protein ratios and electron microscopy. 5. Total plasma iron was 19,760 micrograms/100 ml in larvae and 34 micrograms/100 ml in adults.