Sánchez-Pozzi E J, Catania V A, Rodríguez-Garay E A, Mottino A D
Instituto de Fisiología Experimental, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad Nacional de Rosario, Argentina.
Biochim Biophys Acta. 1995 Dec 14;1245(3):293-8. doi: 10.1016/0304-4165(95)00108-5.
Microsomal membranes from rat small intestine exhibit a higher cholesterol/phospholipid ratio and a lower phosphatidyl-choline/sphingomyelin ratio than those of the liver, which could negatively influence membrane-bound enzymes like bilirubin UDP-glucuronosyltransferase. To study the effect of in vitro modifications in the lipid composition of intestinal microsomes on bilirubin glucuronidating activity, two strategies were employed. On one hand, microsomal lipids were modified in order to mimic those of the liver tissue; on the other hand, cholesterol content of microsomal membranes was increased or decreased with respect to the normal value. Lipid changes were carried out by both an enzyme-mediated and a detergent-mediated procedure. Irrespective of the methodology employed, when a depletion in the cholesterol content was produced, enzyme activity increased about 40%, and when lipid composition approached that of the liver tissue, which not only decreased cholesterol but also modified phospholipid classes, enzyme activity increased about 80%. Both lipid modifications produced a 'fluidification' of microsomal membranes measured by fluorescence anisotropy of 1,6-diphenylhexatriene, being the effect of the approach to the liver higher than that of the decrease of cholesterol. In turn, the enrichment in cholesterol of microsomal membranes led to a decrease of enzyme activity of about 20% and to a 'rigidization' of the membranes. The present findings suggest that in rat intestine, bilirubin glucuronidation is strongly influenced by microsomal lipids. In particular, there seems to be an inverse association between enzyme activity and the cholesterol content of membrane.
大鼠小肠的微粒体膜与肝脏的微粒体膜相比，具有更高的胆固醇/磷脂比和更低的磷脂酰胆碱/鞘磷脂比，这可能会对膜结合酶如胆红素UDP - 葡萄糖醛酸基转移酶产生负面影响。为了研究体外改变肠道微粒体脂质组成对胆红素葡萄糖醛酸化活性的影响，采用了两种策略。一方面，对微粒体脂质进行修饰以模拟肝脏组织的脂质；另一方面，相对于正常值增加或减少微粒体膜的胆固醇含量。脂质变化通过酶介导和去污剂介导的方法进行。无论采用何种方法，当胆固醇含量降低时，酶活性增加约40%；当脂质组成接近肝脏组织时，不仅胆固醇降低，而且磷脂种类也发生改变，酶活性增加约80%。两种脂质修饰都通过1,6 - 二苯基己三烯的荧光各向异性测量使微粒体膜“液化”，接近肝脏组织的效果高于胆固醇降低的效果。反过来，微粒体膜中胆固醇的富集导致酶活性降低约20%并使膜“僵化”。目前的研究结果表明，在大鼠肠道中，胆红素葡萄糖醛酸化受到微粒体脂质的强烈影响。特别是，酶活性与膜的胆固醇含量之间似乎存在负相关。
