Das Debapratim, Roy Sangita, Mitra Rajendra Narayan, Dasgupta Antara, Das Prasanta Kumar
Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India.
Chemistry. 2005 Aug 19;11(17):4881-9. doi: 10.1002/chem.200500244.
To determine the crucial role of surfactant head-group size in micellar enzymology, the activity of Chromobacterium Viscosum (CV) lipase was estimated in cationic water-in-oil (w/o) microemulsions of three different series of surfactants with varied head-group size and hydrophilicity. The different series were prepared by subsequent replacement of three methyl groups of cetyltrimethylammonium bromide (CTAB) with hydroxyethyl (1-3, series I), methoxyethyl (4-6, series II), and n-propyl (7-9, series III) groups. The hydrophilicity at the polar head was gradually reduced from series I to series III. Interestingly, the lipase activity was found to be markedly higher for series II surfactants relative to their more hydrophilic analogues in series I. Moreover, the activity remained almost comparable for complementary analogues of both series I and III, though the hydrophilicity was drastically different. Noticeably, the head-group area per surfactant is almost similar for comparable surfactants of both series I and III, but distinctly higher in case of series II surfactants. Thus the lipase activity was largely regulated by the surfactant head-group size, which plays the dominant role over the hydrophilicity. The increase in head-group size presumably allows the enzyme to attain a flexible conformation as well as increase in the local concentration of enzyme and substrate, leading to the higher efficiency of lipase. The lipase showed its best activity in the microemulsion of 6 probably because of its highest head-group size. Furthermore, the observed activity in 6 is 2-3-fold and 8-fold higher than sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) and CTAB-based microemulsions, respectively, and in fact highest ever in any w/o microemulsions.
为了确定表面活性剂头基大小在胶束酶学中的关键作用，在由三种不同系列、头基大小和亲水性各异的表面活性剂形成的阳离子油包水（w/o）微乳液中，对黏性色杆菌（CV）脂肪酶的活性进行了评估。不同系列是通过用羟乙基（1 - 3，系列I）、甲氧基乙基（4 - 6，系列II）和正丙基（7 - 9，系列III）基团依次取代十六烷基三甲基溴化铵（CTAB）的三个甲基制备而成的。从系列I到系列III，极性头的亲水性逐渐降低。有趣的是，相对于系列I中亲水性更强的类似物，发现系列II表面活性剂的脂肪酶活性明显更高。此外，尽管亲水性差异很大，但系列I和III的互补类似物的活性几乎相当。值得注意的是，系列I和III中可比表面活性剂的每个表面活性剂的头基面积几乎相似，但系列II表面活性剂的头基面积明显更大。因此，脂肪酶活性在很大程度上受表面活性剂头基大小的调节，头基大小比亲水性起主导作用。头基大小的增加可能使酶能够获得灵活的构象，同时增加酶和底物的局部浓度，从而提高脂肪酶的效率。脂肪酶在6号微乳液中表现出最佳活性，可能是因为其头基大小最大。此外，在6号微乳液中观察到的活性分别比双（2 - 乙基己基）磺基琥珀酸钠（AOT）和基于CTAB的微乳液高2 - 3倍和8倍，实际上是任何油包水微乳液中活性最高的。
