Stimulatory effect of phosphate, ATP and ADP on iron transfer from Fe(III)-bleomycin to apotransferrin

1. The rate of ferric ion transfer from Fe(III)-bleomycin to apotransferrin was increased in the presence of orthophosphate, ATP and ADP, while AMP was without effect. 2. Ortho phosphate activation probably involves formation of a Fe(III)-bleomycin-phosphate complex. The optical absorption of Fe(III)-bleomycin at 450 nm is enhanced in the presence of phosphate. 3. ATP and ADP remove the ferric ion from the iron-drug complex; thus making the ferric ion readily available for uptake by apotransferrin. 4. Low concentrations of ATP, ADP and AMP, also enhance the 450 nm absorption of the iron-drug complex. Higher ATP and ADP concentrations reduce both the 450 and 384 nm absorption of Fe(III)-bleomycin.