SDS-PAGE analysis of the cross-linking reactions of human cyt b5 and CYP3A4 using EDC. Holo and apo b5 were cross-linked with CYP3A4 at 1:1 mole ratio in the absence and presence of EDC. A. The holo b5 and CYP3A4 reaction. Lane 1, protein ladder; lane 2, holo b5 + CYP3A4 without EDC; lane 3, holo b5 + CYP3A4 with EDC. B. The apo b5 and CYP3A4 reaction. Lane 1, protein ladder; lane 2, apo b5 + CYP3A4 with EDC; lane 3, apo b5 + CYP3A4 without EDC.