Kaul S, Olson J A
Department of Biochemistry & Biophysics, Iowa State University, Ames 50011, USA.
Int J Vitam Nutr Res. 1998;68(4):232-6.
In keeping with the in vivo observation that the conversion of retinoyl beta-glucuronide (RBG) to retinoic acid (RA) is enhanced in vitamin A-deficient (A-) rats, the relative rates of hydrolysis of RBG to RA by various organelles of liver, kidney and intestine were found to be higher in A- rats than in vitamin A-sufficient (A+) rats (mean ratio 1.28; range 1.05-1.63). The lysosomal fraction of kidney and the microsomal fraction of liver showed the highest ratios for RBG hydrolysis; namely, 1.63 and 1.57, respectively (p < 0.005). The rates of hydrolysis of an ether glucuronide, p-nitrophenyl-beta-D-glucosiduronate (pNPG), were also enhanced in A- rats. The ratios of activities were again highest in kidney lysosomes and in liver microsomes; namely, 1.51 (p < 0.005) and 1.42 (p < 0.05), respectively. The non-ionic detergent, Triton X-100, increased RBG hydrolysis in organelles of A+ (19-27%) more than in those of A- rats (8-14%). The ratios of activities +/- SEM with 0.02% Triton X-100 in organelles of kidney, liver and intestine were 1.25 +/- 0.03, 1.22 +/- 0.03 and 1.24 +/- 0.03 in A+ rats and were 1.11 +/- 0.02, 1.07 +/- 0.02 and 1.13 +/- 0.03, respectively, in A- rats. Thus, Triton X-100 had a significantly greater effect (p < 0.005) on the membranes of A+ rats than on those of A- rats. In conclusion, the increased appearance of RA in the plasma after RBG administration in vivo seems to be caused by enhanced activity of beta-glucuronidases in tissue organelles, augmented in part by better access of the substrate to the membrane-bound enzymes.
与体内观察结果一致，即视黄酰β - 葡萄糖醛酸酯（RBG）向视黄酸（RA）的转化在维生素A缺乏（A - ）大鼠中增强，发现肝脏、肾脏和肠道的各种细胞器将RBG水解为RA的相对速率在A - 大鼠中高于维生素A充足（A + ）大鼠（平均比值1.28；范围1.05 - 1.63）。肾脏的溶酶体部分和肝脏的微粒体部分显示出RBG水解的最高比值；分别为1.63和1.57（p < 0.005）。醚葡萄糖醛酸酯对硝基苯基 - β - D - 葡萄糖醛酸酯（pNPG）的水解速率在A - 大鼠中也有所提高。活性比值在肾脏溶酶体和肝脏微粒体中再次最高；分别为1.51（p < 0.005）和1.42（p < 0.05）。非离子去污剂Triton X - 100对A + 大鼠细胞器中RBG水解的增加幅度（19 - 27%）大于对A - 大鼠细胞器中RBG水解的增加幅度（8 - 14%）。在肾脏、肝脏和肠道细胞器中添加0.02% Triton X - 100后的活性比值±SEM在A + 大鼠中分别为1.25 ± 0.03、1.22 ± 0.03和1.24 ± 0.03，在A - 大鼠中分别为1.11 ± 0.02、1.07 ± 0.02和1.13 ± 0.03。因此，Triton X - 100对A + 大鼠膜的影响比对A - 大鼠膜的影响显著更大（p < 0.005）。总之，体内给予RBG后血浆中RA出现增加似乎是由于组织细胞器中β - 葡萄糖醛酸酶活性增强，部分原因是底物更好地接近膜结合酶。
