Aggregation and Fibril Formation of Plasma Fibronectin by Heparin

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Abstract
The influence of various parameters on the precipitation of [human] plasma fibronectin by heparin was investigated. Rising heparin concentration augmented the precipitation up to a maximum beyond which precipitation decreased. Yields close to 80% were obtained at low temperatures, but some precipitation was observed at 37.degree. C as well. Insolubilization was considerably dependent on the ionic strength, indicating that electrostatic forces play a major role in the aggregation of fibronectin. Ca prevented precipitation by heparin at low concentrations. If precipitation was performed on hydrophobized glass cover slides, the formation of fibrils visible by phase-contrast microscopy was observed. On hydrophilic surfaces amorphous precipitates were generally obtained, most likely due to trapping of aggregates by adsorption prior to their arrangement in fibrils. A model assuming that heparin induces a conformational rearrangement of plasma fibronectin so that masked binding sites responsible for self-association become exposed is discussed.

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