Study on the translocation of chicken heart apocytochrome C with different unfolded states.

Chemically-prepared chicken heart apocytochrome c with different unfolded states could be obtained during the renaturation process. They exhibited distinct circular dichroism patterns designated as Apo C1 (random coiled), Apo C2 (less ordered) and Apo C3 (more ordered). This characteristic is unique to chicken heart apocytochrome c while compared with its counterparts from Candida krusei, tuna heart or horse heart and promises the emergence of much more detail of correlation of translocation with unfolded states of apocytochrome c. When chicken heart apocytochrome c was subjected to a translocation assay in vitro using trypsin-enclosed large unilamellar vesicles from soybean phospholipids, the ability of the protein to penetrate into the liposomes was found to follow the order of Apo C1 > Apo C2 > Apo C3. Conformational alterations of Apo C1, Apo C2 and Apo C3 in association with soybean phospholipid vesicles shown by circular dichroism measurement demonstrated that Apo C1 bound to phospholipids existed in a more loosely folded conformation than Apo C2 and Apo C3. We propose that a more flexible structure of apocytochrome c following the interaction with phospholipids is required for its efficient translocation across the bilayer.