Tissue samples (10 g) of each treatment were homogenized with 25 mL of 100 mmol/L sodium phosphate buffer (pH 6.4) containing 0.5 g of polyvinyl polypyrrolidone (PVPP) and ground at 4 C. The homogenate was centrifuged at 15,000g for 30 min at 4 C and the supernatant was used for the enzyme assay.