Adsorption of proteins onto glass surfaces and its effect on the intensity of circular dichroism spectra.

Errors in analyzing CD spectra of proteins arising from adsorption loss onto glass surfaces were examined for six proteins: apolipoproteins A-I and E, fibronectin, bovine serum albumin, insulin, and glucagon. Among these, the glycoproteins, apolipoprotein E and fibronectin, adsorbed most onto glass surfaces. Their CD intensities decreased by about 50% when proteins were diluted serially from 1 to 0.01 mg/ml in regular glass-ware and CD was measured in uncoated cells. The other proteins, except glucagon, also showed a certain degree of adsorption. Thus, adsorption loss of proteins onto glass surfaces is common and may lead to serious errors in experimental results. Adsorption can be minimized by using plastic containers and pipet tips, coating the cell with silicone, and wetting the cell before adding the protein solution.