IRP1 protein level in LY cells. Twenty micrograms of cell extracts were separated on an 8% sodium dodecyl sulfate–polyacrylamide gel and transferred to a nitrocellulose membrane. IRP1 was detected with a specific antiserum by the ECL method. Recombinant human IRP1 was used as standard. Two separate experiments produced similar results; n.s. indicates nonspecific band.