Determination of carboxylesterase in rat tissues and blood using riboflavin-5'-monobutyrate.
作者:JUN OKUDA、NORIHIRO HORIGUCHI
DOI:10.1248/cpb.28.181
日期:——
Riboflavin-5'-monobutyrate (R-MB, mp 244-245°) was synthesized from riboflavin and butyric anhydride (yield : 10%) as well as from riboflavin-2', 3', 4', 5'-tetrabutyrate and hydrazine hydrate (yield : 44%). Riboflavin-5'-monopalmitate (R-MP, mp 228-230°) was also prepared from riboflavin and palmitic anhydride (yield : 9.8%). The absorption, fluorescence, and infrared spectra, and Rf values of R-MB and R-MP are given. R-MP was hardly hydrolyzed by pure hog hepatic carboxylesterase. However, R-MB was readily hydrolyzed to riboflavin by pure hog hepatic carboxylesterase, though not by pure pancreatic lipase (triacylglycerol lipase), acetylcholinesterase, or cholinesterase. The activity of carboxylesterase could therefore be estimated by fluorometric determination of riboflavin hydrolyzed from R-MB. The optimum incubation conditions for the assay of carboxylesterase with R-MB were pH 7, 37°, 15 min. Studies on the rat organs and liver subcellular distributions of carboxylesterase showed that the enzyme is localized in the small intestine, kidneys, lungs, heart, and blood, and high carboxylesterase activity was demonstrated in the microsomal fraction in rat liver. R-MB was a rather specific substrate for carboxylesterase, permitting selective assay of this enzyme activity.
核黄素-5'-单丁酸酯(R-MB,熔点244-245°)由核黄素和丁酸酐合成(收率:10%)以及核黄素-2'、3'、4'、5'-四丁酸酯和水合肼(收率:44%)。核黄素-5'-单棕榈酸酯(R-MP,熔点228-230°)也由核黄素和棕榈酸酐制备(产率:9.8%)。给出了 R-MB 和 R-MP 的吸收光谱、荧光光谱、红外光谱以及 Rf 值。 R-MP 很难被纯猪肝羧酸酯酶水解。然而,R-MB 很容易被纯猪肝羧酸酯酶水解为核黄素,但不能被纯胰脂肪酶(三酰甘油脂肪酶)、乙酰胆碱酯酶或胆碱酯酶水解。因此,可以通过荧光测定从 R-MB 水解的核黄素来估计羧酸酯酶的活性。用 R-MB 测定羧酸酯酶的最佳孵育条件为 pH 7、37°、15 分钟。对大鼠器官和肝脏亚细胞中羧酸酯酶分布的研究表明,该酶定位于小肠、肾脏、肺、心脏和血液中,并且在大鼠肝脏的微粒体部分中显示出高羧酸酯酶活性。 R-MB 是羧酸酯酶的一种相当特异的底物,允许选择性地测定这种酶的活性。