Stanley D W., Sarath G, Rana R L.
Insect Biochemistry/Physiology Laboratory, Department of Entomology, University of Nebraska, Lincoln, USA
J Insect Physiol. 1998 Mar;44(3-4):297-303. doi: 10.1016/s0022-1910(97)00118-2.
We hypothesized that phospholipase A(2) (PLA(2)) is a common feature of insect digestive physiology. PLA(2) hydrolyzes polyunsaturated fatty acids (PUFAs) associated with the sn-2 position of phospholipids (PLs). We describe here a PLA(2) from midgut contents of the tobacco hornworm, Manduca sexta. Our results indicate that the enzyme is sensitive to pH (inactivated at low pH), protein concentration (up to 1.6&mgr;g/&mgr;l), substrate concentration (up to 1.4nmoles/reaction), temperature (up to 30 degrees C), and incubation time. We also found that PLA(2) activity is higher in fed than in starved larvae, and enzyme activity is associated with the midgut contents, rather than the midgut epithelium of fed larvae. All known secretory PLA(2)s, except for a PLA(2) in venom of the marine snail, Conus magus, require high calcium concentrations for catalysis, but the Manduca PLA(2) appears to be calcium-independent, and it exhibits increased PLA(2) activity in the presence of a calcium-chelator, EGTA. In addition, the partially purified Manduca PLA(2) is not inhibited by the phospholipid analog, oleyloxyethylphosphorylcholine. These findings suggest that the Manduca digestive PLA(2) may represent another novel form of PLA(2).
我们推测磷脂酶A(2)（PLA(2)）是昆虫消化生理学的一个共同特征。PLA(2)可水解与磷脂（PL）的sn-2位相关的多不饱和脂肪酸（PUFA）。我们在此描述了一种来自烟草天蛾（Manduca sexta）中肠内容物的PLA(2)。我们的结果表明，该酶对pH（在低pH下失活）、蛋白质浓度（高达1.6μg/μl）、底物浓度（高达1.4纳摩尔/反应）、温度（高达30摄氏度）和孵育时间敏感。我们还发现，取食幼虫的PLA(2)活性高于饥饿幼虫，且酶活性与中肠内容物相关，而非取食幼虫的中肠上皮。除了海蜗牛Conus magus毒液中的一种PLA(2)外，所有已知的分泌型PLA(2)都需要高钙浓度来进行催化，但烟草天蛾PLA(2)似乎不依赖钙，并且在存在钙螯合剂乙二醇双四乙酸（EGTA）的情况下其PLA(2)活性会增加。此外，部分纯化的烟草天蛾PLA(2)不受磷脂类似物油酰氧乙基磷酰胆碱的抑制。这些发现表明，烟草天蛾消化型PLA(2)可能代表了PLA(2)的另一种新形式。
