Moorhouse K G, Logan C J, Hutson D H, Dodds P F
Department of Biochemistry and Biological Sciences, Wye College, (University of London), Ashford, Kent, U.K.
Biochem Pharmacol. 1990 May 15;39(10):1529-36. doi: 10.1016/0006-2952(90)90517-o.
The incorporation of 3-phenoxybenzoic acid (3PBA) into xenobiotic lipids by enzymes of the monoacylglycerol (MG) pathway was measured using microsomes prepared from rat liver as an enzyme source. The mean activities of the three enzymes involved were: acyl-CoA synthetase, 1.1 nmol/min/mg protein; MG acyltransferase, 75 pmol/min/mg protein; and diacylglycerol acyltransferase, 11.4 pmol/min/mg protein. MG and DG acyltransferase also showed activity with benzoyl-CoA or 1-naphthylacetyl-CoA as acyl donor but none with clofibryl-CoA or 2,4-dichlorophenoxyacetyl-CoA. MG acyltransferase activity, using 3PBA-CoA, was higher in microsomes from rat intestinal mucosa and pig liver, and lower in rat adipose tissue, rat liver and mouse liver. This ranking of activities corresponds to published activities using natural substrates. There was a large increase in MG acyltransferase, using either 3PBA-CoA or palmitoyl-CoA as substrate, in microsomes from the livers of rats 16-18 days old. Lysophosphatidic acid (lyso-PA) and lysophosphatidylethanolamine (lyso-PE), but not other phospholipids or detergents, stimulated MG acyltransferase activity more than two-fold. Lyso-PA (5 microM) increased the Vmax but had little effect on the Km for 2-hexadecylglycerol, whereas 100 microM lyso-PE decreased the Km and had a smaller effect on the Vmax. These results illustrate that the incorporation of xenobiotic acids into diacyl- and triacylglycerol by enzymes of the MG pathway may be a more general phenomenon than was previously suspected and that it may be subject to a variety of developmental and physiological controls.
使用从大鼠肝脏制备的微粒体作为酶源，测定了单酰甘油（MG）途径的酶将3-苯氧基苯甲酸（3PBA）掺入外源性脂质的情况。所涉及的三种酶的平均活性分别为：酰基辅酶A合成酶，1.1 nmol/分钟/毫克蛋白；MG酰基转移酶，75 pmol/分钟/毫克蛋白；二酰甘油酰基转移酶，11.4 pmol/分钟/毫克蛋白。MG和DG酰基转移酶以苯甲酰辅酶A或1-萘乙酰辅酶A作为酰基供体时也表现出活性，但以氯贝丁酯辅酶A或2,4-二氯苯氧基乙酰辅酶A作为酰基供体时则无活性。使用3PBA-CoA时，MG酰基转移酶活性在大鼠肠黏膜和猪肝的微粒体中较高，而在大鼠脂肪组织、大鼠肝脏和小鼠肝脏中较低。这种活性排序与使用天然底物时已发表的活性一致。在16 - 18日龄大鼠肝脏的微粒体中，以3PBA-CoA或棕榈酰辅酶A作为底物时，MG酰基转移酶活性大幅增加。溶血磷脂酸（lyso-PA）和溶血磷脂酰乙醇胺（lyso-PE），而非其他磷脂或去污剂，使MG酰基转移酶活性增加了两倍多。5 microM的lyso-PA增加了Vmax，但对2-十六烷基甘油的Km影响很小，而100 microM的lyso-PE降低了Km，对Vmax的影响较小。这些结果表明，MG途径的酶将外源性酸掺入二酰甘油和三酰甘油中可能是一种比先前怀疑的更为普遍的现象，并且可能受到多种发育和生理控制。
