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B. Danysh, T. P. Patel, D. A. Edwards, K. J. Czymmek, M. K. Duncan; Sulfate and Carboxyl Groups Within the Anterior Lens Capsule Regulates Diffusion and Interactions of Charged Proteins. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1524. doi: https://doi.org/.
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The lens capsule is a thick basement membrane composed of a complex matrix of molecules. It is considered selectively permeable to molecules important for normal lens function but limiting passage of others. Anionic sites within the capsule matrix have been proposed to contribute to the protein-matrix interactions and diffusion rates. We test the hypothesis that sulfate and carboxyl groups within the capsule matrix regulate interactions and diffusion of charged proteins.
We employed Fluorescence Recovery After Photobleaching (FRAP) on the capsules of intact mouse lenses and a novel mathematical algorithm to determine diffusion coefficients and binding rate constants of FITC labeled neutral dextrans and several proteins (albumin, EGF, and alpha, beta, and gamma crystallins). The negative charge of sulfate carboxyl groups was neutralized by heparinase treatment while carboxyl groups were neutralized by methylation.
Charged proteins have significantly lower diffusion constants and higher binding rate constants within the lens capsule than neutral dextrans of similar Stokes radii. Charge neutralization of sulfate and carboxyl groups within the capsule significantly increase binding rate constants of charged but not neutral proteins. Diffusion coefficients decreased for negatively charged proteins and increased for positively charged proteins.
We demonstrate that the anionic sites within the lens capsule influence the binding rate constants as well as diffusion rates of charged proteins. These sites play an important part in the mechanism allowing anionic proteins to pass into the lens by minimizing protein-matrix interactions.
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