Tunaz Hasan, Stanley David W
Insect Biochemical Physiology Laboratory, University of Nebraska-Lincoln, 311 Plant Industry Building, Lincoln, NE 68583-0816, USA.
Comp Biochem Physiol B Biochem Mol Biol. 2004 Sep;139(1):27-33. doi: 10.1016/j.cbpc.2004.05.010.
We describe a phospholipase A2 (PLA2) associated with the salivary glands of tobacco hornworms, Manduca sexta. This enzyme is able to hydrolyze arachidonic acid from the sn-2 position of PLs. Addition of the calcium chelator, EGTA, or calcium, to the Tris reaction buffer impaired the PLA2 activity, from which we infer the enzyme requires very low concentrations of calcium or perhaps other ions for optimal activity. PLA2 activity was sensitive to protein concentration (highest activity at 25 microg protein per microl), reaction time (optimal at 30 min), buffer pH (optimal at pH 8-10), and reaction temperature (optimal range 18-38 degrees C). The salivary gland PLA2 was sensitive to the site-specific inhibitor, oleyloxyethylphosphorylcholine and stable to freezing at -80 degrees C, but not -20 degrees C. The biological significance of this enzyme may relate to hydrolysis of fatty acid moieties from dietary PLs for absorption by midgut epithelia. This salivary gland enzyme may also be responsible for killing food-borne bacteria.
我们描述了一种与烟草天蛾（Manduca sexta）唾液腺相关的磷脂酶A2（PLA2）。这种酶能够从磷脂的sn-2位水解花生四烯酸。向Tris反应缓冲液中添加钙螯合剂EGTA或钙会损害PLA2的活性，由此我们推断该酶需要极低浓度的钙或其他离子来实现最佳活性。PLA2活性对蛋白质浓度（每微升25微克蛋白质时活性最高）、反应时间（30分钟时最佳）、缓冲液pH（pH 8 - 10时最佳）和反应温度（最佳范围18 - 38摄氏度）敏感。唾液腺PLA2对位点特异性抑制剂油酰氧基乙基磷酰胆碱敏感，在-80摄氏度可冷冻保存，但在-20摄氏度不行。这种酶的生物学意义可能与从膳食磷脂中水解脂肪酸部分以供中肠上皮吸收有关。这种唾液腺酶也可能负责杀死食源细菌。
