The liver homogenate was used for activity analysis of metabolic enzyme. The activities of aspartate transaminase (AST) and alanine transaminase (ALT) were measured by automatic biochemistry analyzer (Hitachi 7020, Tokyo, Japan). One unit (U g−1prot) of AST is defined as the amount of enzyme in 1g tissue protein that generated 1.0 µmol of glutamate per minute at pH 8.0 and 37 °C. One unit (U g−1prot) of ALT is defined as the amount of enzyme in 1g tissue protein that generated 1.0µmol of pyruvate per minute, at pH8.0 and 37 °C. Fatty acid synthase (FAS), hepatic lipase (HL), glycogen synthetase (GCS), glucokinase (GK), pyruvate carboxylase (PC) were analyzed using Activity Assay Kit (Solarbio Science & Technology Co., Ltd, Beijing, PR China). One unit (U mg−1 prot) of FAS activity was defined as the amount of enzyme in 1 mg tissue protein that oxidize 1.0 µmol NADPH per minute at pH 7.8 and 37 °C. One unit (U mg−1prot) of HL activity is defined as the amount of enzyme in 1 mg tissue protein that generate 1.0 µmol naphthylester from α-naphthalene acetate per minute at pH 7.8 and 37 °C. One unit (U mg−1prot) of GCS activity is defined as the amount of enzyme in 1 mg tissue protein that oxidize 1.0 nmol NADH per minute at pH 7.8 and 37 °C. One unit (U mg−1prot) of GK activity is defined as the amount of enzyme in 1 mg tissue protein convert 1 pmol of NADP to NADPH at 30 °C. One unit (U mg−1prot) of PC activity is defined as the amount of enzyme in 1 mg tissue protein convert 1.0 mmol of pyruvate and CO2 to oxalacetate per minute at pH 7.8 at 30  °C.

Activity of hepatic cysteine sulfinate decarboxylase (CSD) was determined according to the method reported by Goto et al. (2001), Goto et al. (2003) and Yokoyama et al. (2001). In brief, isolated livers were homogenized in 0.25 M sucrose and dialyzed against 10 mM phosphate buffer (pH 7.4) for 4 h to remove the endogenous taurine at 4 °C.The incubation mixture consisted of 100 mM sodium phosphate buffer (pH 7.2), 1.0 mM cysteinesulfinate, 0.2 mM pyridoxal 5′-phosphate, 4 mM 2-mercaptoethanol. The reaction was started by the addition of the crude enzyme solution (1 mg protein) and the incubation was continued at 35 °C for 1 h. After the reaction mixture was heated at 70  °C for 3 min to end the reaction, β-alanine (0.2 mmol) was added as an internal standard. Amino acid analysis was performed by reverse-phase HPLC with o-phthalaldehyde as a prelabeling. The taurine content formed by the H2O2 treatment was calculated by the area ratio of taurine to β-alanine and regarded as the enzyme activity.

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