Figure 4.

Subunit exchange with apoC-II fibrils. Panel A: Alexa488-labelled apoC-II monomer was added to preformed apoC-II fibril samples (closed circles) or purified closed-loops (open circles). Subunit exchange was monitored by centrifugation of the samples and determination of the Alexa labelled apoC-II fluorescence in the supernatant fraction. Panel B: Alexa488 fluorescence emission measured as a function of time for monomeric Alexa488-labelled apoC-II added to linear fibrils (closed circles), purified closed-loops (open circles), linear fibrils alone (closed triangles) and closed loops alone (open triangles). The fluorescence of free Alexa488-maleimide (0.76 µM), following the addition apoC-II fibrils (15.7 µM), expressed relative to the fluorescence of Alexa488-maleimide alone (closed squares). Panel C: Sedimentation velocity subunit exchange analysis of preformed and closed-loop apoC-II fibrils. Monomeric Alexa488-labelled apoC-II (0.016 mg/ml) was incubated with preformed fibrils or purified closed-loops (0.14 mg/ml) for 4 hrs at 25°C. Sedimentation coefficient distribution analysis was performed at 280 nm to detect total protein for preformed fibrils or purified closed-loops (solid and dashed line, respectively) and at 495 nm to monitor the distribution of Alexa488-labelled apoC-II in preformed fibrils or purified closed-loops (dotted line and dot-dot-dash lines, respectively).