HOST HEMOLYMPH MONOPHENOLOXIDASE ACTIVITY IN PARASITIZED MANDUCA-SEXTA LARVAE AND EVIDENCE FOR INHIBITION BY WASP POLYDNAVIRUS
HOST HEMOLYMPH MONOPHENOLOXIDASE ACTIVITY IN PARASITIZED MANDUCA-SEXTA LARVAE AND EVIDENCE FOR INHIBITION BY WASP POLYDNAVIRUS
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DOI：
10.1016/0020-1790(90)90046-w
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发表时间：
1990-01-01
期刊：
影响因子：
--
通讯作者：
DEBURON, I
中科院分区：
文献类型：
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作者：
BECKAGE, NE;METCALF, JS;DEBURON, I
在昆虫中，抵御寄生虫的主要途径之一是被血细胞包裹，然后进行黑化，其中酪氨酸和多巴通过有毒的醌中间体转化为黑色素。本报告描述了使用体外放射化学测定来监测血淋巴单酚氧化酶 (MPO) 将 [3H] 酪氨酸转化为 [3H]DOPA，所用方法采用先前用于双翅目和哺乳动物酶的方法。短毛蜂 Cotesia congregata 对第五龄烟草天蛾幼虫的寄生降低了宿主体内血淋巴单酚氧化酶的活性。在新寄生的幼虫和末期宿主中可检测到血淋巴 MPO 的显着抑制。在注射蔗糖梯度纯化的黄蜂多DNA病毒（PDV）颗粒后，在未寄生的幼虫中观察到类似的效果，这些颗粒通常由宿主体内的雌性黄蜂注射，这表明这种抑制可能是病毒介导的。体内注射 PDV 24 小时后，体外测定血淋巴 MPO 活性，并通过暴露于补骨脂素和长波紫外线来插入病毒 DNA。光消除了其对 MPO 的抑制作用。尽管寄生抑制了血淋巴 MPO 活性，但宿主角质层酶似乎未受影响，因为在黄蜂从宿主中出现时，表皮受伤部位发生了角质层黑色化。被寄生和注射病毒的幼虫的背血管和体皮中出现红色素；这些色素沉着的变化是否与寄生对酪氨酸代谢和色素生物合成的影响有关仍有待确定。
In insects, one of the primary routes of defense against parasities is encapsulation by hemocytes followed by melanization, in which tyrosine and DOPA are converted to melanin via toxic quinone intermediates. This report describes the use of an in vitro radiochemical assay to monitor hemolymph monophenoloxidase (MPO) conversion of [3H]tyrosine to [3H]DOPA, using a method utilized previously for dipteran and mammalian enzymes. Parasitism of fifth instar tobacco hornworm larvae by the brachonid wasp Cotesia congregata depresses the rate of hemolymph monophenoloxidase activity in the hosts. Significant inhibition of hemolymph MPO was detectable in newly parasitized larvae and terminal stage hosts. A similar effect was seen in unparasitized larvae following injection of sucrose-gradient purified wasp polydnavirus (PDV) particles, which are normally injected by the female wasps in the host, suggesting the inhibition may be virally mediated. Hemolymph MPO activity was assayed in vitro 24 h after injection of PDV in vivo, and intercalation of viral DNA by exposure to psoralen and long-wave u.v. light eliminated its inhibitory effect on MPO. Despite inhibition of hemolymph MPO activity by parasitism, host cuticular enzymes appear unimpaired, since cuticular melanization occurs at sites of integumental wounding during emergence of the wasps from the host. Red pigments appear in the dorsal vessel and integument of parasitized and virus-injected larvae; whether these pigmentation changes are related to effects of parasitism on tyrosine metabolism and ommochrome biosynthesis remains to be determined.