Comparison of Dihydrofolate Reductase Activities for Folic Acid in Pigs and Rats Using In Vivo and In Vitro Evaluation Techniques
2001 年 47 巻 2 号 p. 96-101
詳細
2001 年 47 巻 2 号 p. 96-101
The activity of dihydrofolate reductase (DHFR) for folic acid (PteGlu) was eval-uated in pigs by in vivo and in vitro experiments. The results were compared with those of rats. Since bile secretion of reduced folates reflects the activity of DHFR for PteGlu in the body, the bile secretion rates of reduced folates including tetrahydrofolate (H4PteGlu), 5-methyltetrahydrofolate, 5, 10-methylenetetrahydrofolate, and 10-formyltetrahydrofolate were determined by using high-performance liquid chromatography with electrochemical detection, after the intravenous injection of PteGlu at 1 mg/kg body weight to pigs and rats. Although the PteGlu injection raised the total secretion rate of reduced folates, the total in-creased amount of reduced folates secreted into bile from 0 h to 2.5 h after PteGlu injection in pigs was about one-tenth of that in rats. The enzyme kinetics of DHFR for PteGlu was ex-amined at the physiological condition (pH 7.4 and 3 7°C). Affinity chromatography was ap-plied to liver homogenates of pigs and rats to obtain DHFR. The final product of the enzyme reaction, H4PteGlu, was measured. The Km for pig enzyme was similar to that for rat en-zyme, whereas the Vmax for the pig enzyme was less than 1/5 of that for the rat's. The com-parison of the ratio of Vmax to Km between pig and rat enzymes suggests that PteGlu is a much less efficient substrate for pig liver DHFR. In short, these results from in vivo and in vitro experiments suggest that the role of DHFR for PteGlu in pigs is physiologically much less important than that in rats.
