Measuring the Length Distribution of a Fibril System:  A Flow Birefringence Technique Applied to Amyloid Fibrils

• Published in: Macromolecules Vol. 38; no. 7; pp. 2948 - 2958
• Main Authors: Rogers, Salman S, Venema, Paul, Sagis, Leonard M. C, van der Linden, Erik, Donald, Athene M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 05.04.2005
• Subjects: Analytical, structural and metabolic biochemistry; Applied sciences; beta-lactoglobulin gels; Biological and medical sciences; carbon nanotubes; disease; Exact sciences and technology; fibers; Fundamental and applied biological sciences. Psychology; General aspects, investigation methods; macromolecules; Natural polymers; Physicochemistry of polymers; polydispersity; protein; Proteins; rheooptical response; rodlike chains subject; transient shear-flow; Flow birefringence; Shear flow; Optical method; Amyloid; Measurement method; Aqueous solution; Experimental study; Dimension spectrum; Protein; Fibril
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma0474224

Relaxation of flow birefringence can give a direct measure of the rotational diffusion of rodlike objects in solution. With a suitable model of the rotational diffusivity, a length distribution can be sought by fitting the decay curve. We have measured the flow birefringence decay from solutions of amyloid fibrils composed of β-lactoglobulin and extracted a length distribution using the Doi−Edwards−Marrucci−Grizzuti theory of semidilute rotational diffusion. The concentration scaling of the results shows that the fibrils diffuse as free rods:  they cannot be significantly branched, sticky, or break up under dilution. The length distribution obtained shows a single broad peak, consistent with measurements of the fibrils by electron microscopy. This comparison, and combination of the experiment with an assay to find the total concentration of fibrils, allows calibration of the length scale and concentration scale of the length distribution. It is our hope that this method can be used for following the growth kinetics of amyloid fibrils in vitro and for studying the length distribution of rodlike systems in general.