PRODUCTION AND CHARACTERIZATION OF RECOMBINANT HETEROPOLYMERS OF HUMAN FERRITIN H-CHAIN AND L-CHAIN

Vertebrate ferritins are iron storage proteins composed by 24 subunits of one or more types. The recombinant homopolymers of human ferritin H- and L-type chains differ in iron uptake and in physical stability, but the properties of heteropolymers with various proportions of H- an d L-type chains cannot be predicted. Present study shows that unfolded human ferritin Hand L- type chains renature under similar conditions to form homopolymers indistinguishable from the native ones and that, when mixed, the unfolded H and L chains renature to form heteropolymer s with restricted heterogeneity and with the expected H:L ratios. Seve n of these ferritins with different H:L ratios were analyzed; electrop horetic mobility, immunological reactivity, and stability to guanidine denaturation varied as predicted, based on the homopolymers. In contr ast, the rate of iron uptake, monitored by the variation of absorbance at 310 nm, increased in the ferritins that ranged in H chain content from 0 to 35%; further increments in H chains had no additional effect . This finding indicates that, under the present conditions, only a li mited number of H chains are needed for the maximum rate of ferritin i ron uptake. Variations of L- and H-type chains in vivo may thus have b iological relevance.