2.8 Total soluble protein (TSP) measurement
TSP in the sample was determined by the Bradford assay (Bradford, 1976) using Bio-Rad protein assay dye reagent (Bio-Rad, Hercules, CA). The standard curve of 0.05 to 0.5 mg/mL bovine serum albumin (BSA; Sigma-Aldrich, St. Louis, MO) was generated along with the samples. The absorbance at 595 nm of the samples and standards were analyzed in triplicate with a SpectraMax 340PC spectrophotometer (Molecular Devices, Sunnyvale, CA).