Abstract
mammals. When excess iron was injected, mature red cells of larvae accumulated ferritin iron (increased from 200 pg/ml of cells to 410 pg/ml of cells) and ferritin protein (increased from 0.37 to 1.2% of the soluble protein), which resulted from the de novo synthesis of subunits (increased from 1.9 to 6.3% of the total protein synthesized); there was no detectable ferritin subunit pool. Iron did not change ferritin microheterogeneity. Ferritin synthesis was more sensitive (2-5 times) to inhibitors of translation than total protein syfithesis, indicating that iron may affect the translation of ferritin mRNA as previously observed in rat liver. In vitro, either transferrin or iron-nitrilotriacetic acid donated iron to red cells and ferritin; maximum uptake occurred with a combination of both donors. Iron storage in the larval red cell was similar to liver, except for the apparent absence of a ferritin subunit pool in red cells. Moreover, red cells were more efficient than the liver in acquiring iron for storage, and earlier studies showed that red cell iron stores were used more rapidly than liver stores;, the accessibility of red cells for iron storage may relate to their role in ontogeny. Although an ontogenetic decrease in available iron (transferrin) occurs which could affect red cell iron storage, increasing available iron experimentally had no effect on mature red cells of adults, suggesting an ontogenetic change at the cellular level independent of the change in transferrin.
Highlights
Red cells were more efficient than the liver Since the mature recdells of the adult incorporated little iron in acquiring iron for storage, and earlier studies and were unresponsive to changeisn available iron,a cellular showed that red cell iron storews ere used more rapidly change occurred in red celilron metabolism during ontogeny than liver stores;,the accessibility of red cells for iron in addition to the extracellular change in transferrin
An ontogenetic decrease in available iron occurs which could affecrted cell iron storage, increasing available iron experimentally had no effect on ma
A similar effect of iron in rat liver has been explained by Regulation of red cell ferritin synthesis in amphibian larvae proposing a n increase in assembly of ferritin subunitsleading
Summary
The uptake of iron by red cells was measured by incubating 1% suspensions at 22.5"C for 30 min as previously described (17), with leucine added at a concentration of 83pg/ml since the medium described had no leucine. Plasma transferrin was labeled with 59Fenitrilotriacetic acid a t room temperature for 25 min (IO).The concentration of iron in the incubation mixture was varied either by increasing the concentration of plasma to which 59Fe-nitrilotriaceticacid (18) had been added (19ng/100 pl,transferrin saturated to a level of 61%) or by increasing the amount of iron added to 25p1of plasma (the maximum amount added was enough to saturate times the amount of transferrin present). The incubation was terminated by adding the cells to 2 volumes of ice-coId amphibian Ringer's solution without calcium (17), washing the cells 4 times and lysing them, either by repeated freeze-thawing or by water and CHCL (17) or with ethylacetate-acetic acid (19), which fractionated the cells into heme and non-heme components. An absorbance value of 0.90 was equivalent to 1ml of 1% red cell suspension
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