Multiple peak formation from reversed-phase liquid chromatography of recombinant human platelet-derived growth factor

Reversed-phase liquid chromatography of recombinant platelet-derived growth factor (PDGF) results in the appearance of at least four distinguishable peaks. The relative areas of these peaks are, in part, dependent upon the gradient time and the temperature. Isolation and reinjection of each peak gave chromatographic profiles comparable to that obtained from unfractionated PDGF. Increasing the temperature above 60 degrees C resulted in a single peak that, when isolated and reinjected at ambient temperature, produced a chromatogram comparable to PDGF which had not been exposed to elevated temperature. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that all four peaks had the same molecular mass as PDGF and were active as determined by a PDGF mitogenic bioassay. These results indicate that multiple conformations of PDGF are present and we postulate that their appearance may be a result of isomeric structures arising from the presence of Pro-Pro bonds within the primary structure of the protein.