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Capillary Dilatometry, In Conjunction with UV Spectrophotometry, Measures Conversion of Insulin to Polymeric Protein Fibrils (Amyloid)
Author(s) -
Carman Peter J.,
Kahn Peter C.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.914.1
Subject(s) - insulin , amyloid (mycology) , chemistry , fibril , amyloid fibril , polymerization , biophysics , hormone , medicine , chromatography , endocrinology , biochemistry , biology , organic chemistry , amyloid β , polymer , inorganic chemistry , disease
Insulin, which is produced by the pancreas, is a hormone that permits muscle, fat, and liver cells to absorb glucose from the blood. Diabetics who produce insufficient levels of insulin may take the hormone through injection. Repeated insulin injection often causes localized amyloidosis, a poorly understood process characterized by the misfolding of insulin into insoluble polymeric protein fibrils. The dose circulating in the blood is then less than the administered dose with attendant medical consequences. In this work, we followed the misfolding of insulin to its amyloid state through the measurement of the volume change of the reaction. This thermodynamic parameter, the change in volume per mole of native insulin polymerized to amyloid, was measured by capillary dilatometry in conjunction with UV spectrometry. The change in volume is due to water expulsion from the surface of native insulin upon amyloid formation. Preliminary experiments indicate volume change of 200–400 mL/mol of insulin polymerized. The data are being used to estimate the number of water molecules expelled, and we are investigating the possibility of determining the entropy change upon polymerization. Fluctuations from one experiment to the next suggest the presence of additional variables not yet accounted for. Electron microscopy of the amyloid product shows distinct fibrils. Accordingly, future directions include further electron microscopy to analyze how amyloid fibril size affects the amyloid conversion rate.