Erythrocyte haemolysate interacts with ATP-Fe to form a complex containing iron, ATP and 13 800 MW polypeptide.
Iron first entering the reticulocyte is bound to ATP in the low MW cytosolic pool; some is also 'loosely bound' to haemoglobin, coeluting with haemoglobin from a molecular sieve column though not incorporated into haem. When haemolysate is mixed with ATP-Fe in vitro a similar high MW iron-containing complex is formed: the ATP-Fe interacts with a non-haemoglobin constituent of the haemolysate to form a high MW ATP-Fe complex in which the ratio of ATP:Fe (originally 6:1) is reversed, so that the complex contains more iron than ATP. The high MW ATP-Fe complex is formed even when ATP is in 150-fold molar excess and is formed without detectable hydrolysis of the ATP. The activity of haemolysate in forming the high MW ATP-Fe complex is not diminished by dialysis; all of the activity is recovered in the haemoglobin-containing fraction obtained from an Ultrogel AcA 44 column. The activity does not derive from haemoglobin since 85% of the activity is removed when haemoglobin is purified from haemolysate with DEAE-Sephadex. The chelatable iron pool of the cell probably includes both the high MW ATP-Fe complex and low MW ATP-Fe. Shunting of ATP-Fe to a high MW aggregate reduces the amount of iron present in the highly reactive low MW form and thus probably serves to limit the formation of cell damaging radicals.
Weaver
J
J
Albert Einstein College of Medicine, Bronx, New York 10461.
Zhan
H
H
Pollack
S
S
D000255:Adenosine Triphosphate / Q000097:blood*; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D006168:Guinea Pigs; D006461:Hemolysis; D007501:Iron / Q000097:blood*; D046911:Macromolecular Substances; D008970:Molecular Weight; D010455:Peptides / Q000097:blood*; D012156:Reticulocytes / Q000378:metabolism*
D046911:Macromolecular Substances; D010455:Peptides; D000255:Adenosine Triphosphate; D007501:Iron