Copper incorporation into superoxide dismutase in Menkes lymphoblasts

The incorporation of copper into Cu,Zn-superoxide dismutase (SOD) was examined in Menkes lymphoblasts that express a genetic defect of copper metabolism. SOD activity was ≃40% higher in Menkes than normal lymphoblasts. Since Menkes lymphoblasts contain elevated copper levels, the higher SOD activity is most likely due to near copper saturation of an apoSOD pool that is in normal lymphoblasts. Cycloheximide markedly inhibited ⁶⁴Cu(II) incorporation into SOD in Menkes lymphoblasts under conditions in which no significant, de novo synthesis of SOD protein was detected with normal lymphoblasts. The maximal amount of ⁶⁴Cu incorporation into newly synthesized SOD in Menkes lymphoblasts was approximately equal to the maximal amount of ⁶⁴Cu that could be incorporated into the apoSOD pool in normal lymphoblasts. The increased synthesis of SOD in Menkes lymphoblasts may play a protective role against copper toxicity in Menkes lymphoblasts. The protonophore, CCCP markedly inhibited ⁶⁴Cu incorporation into SOD in both normal and Menkes lymphoblasts, which is consistent with ⁶⁴Cu incorporation into SOD within a membrane-bounded compartment in both cell types. When ⁶⁴Cu-incorporation into SOD was blocked with CCCP, copper accumulated in a Superose column fraction that contains S-adenosylhomocysteine hydrolase (SAHH), which has a high affinity for copper. SAHH may play a role in delivering copper to SOD.