Date of Award

6-2011

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Biology

Second Department

Physics and Astronomy

First Advisor

Jay Newman

Second Advisor

Brian Cohen

Language

English

Keywords

protein, dynamic light, DLS, insulin, kinetics, cows

Abstract

In the fields of protein science and medicine, understanding the kinetics of protein aggregation are significant in the research and treatment of certain amyloid diseases such as Alzheimer’s. Previous studies have suggested that arginine can increase the solubility of certain proteins, suppress protein aggregation, and assist in the refolding of aggregated proteins; however, the molecular mechanisms by which arginine can influence protein aggregation are still unclear. Bovine insulin was employed as a model system for further understanding the effects of arginine on protein aggregation. Using Dynamic Light Scattering (DLS), we studied the concentration-dependent and temperature-dependent suppression of aggregation in insulin by means of arginine. Arginine concentrations from 10mM to 500mM were shown to have produced a concentration-dependent increase in the lag time of the aggregation, which is the period preceding protein aggregation. DLS measurements of insulin in the presence of arginine from 60°C to 85°C showed a significant increase in the aggregation delay for samples with arginine compared to control samples without arginine. Arginine samples were shown to have delayed aggregation by up to a factor of 7.5. From Arrhenius analysis, we also found that the activation energy of 1mM insulin was 17 ± 5 kcal/mol while the energy of the insulin samples with 500mM arginine was higher (26 ± 3 kcal/mol). These energy values are in accordance with the energy associated with β-sheet formation, which is about 0.5 kcal/mol/residue (or ~25 kcal/mol for monomeric insulin). The 9 kcal/mol difference may quantify the barrier effect of arginine on insulin aggregation.

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