Valenzuela J G, Ribeiro J M
Medical Entomology Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Building 4, Room 126, Bethesda, MD 20892, USA.
J Exp Biol. 1998 Sep;201(Pt 18):2659-64. doi: 10.1242/jeb.201.18.2659.
Cimex lectularius and Rhodnius prolixus contain salivary nitric oxide (NO) that may help them to feed on their vertebrate hosts by promoting vasodilation and inhibiting platelet aggregation. Salivary NO is associated with heme proteins (nitrophorins) that store and transport NO from the insect salivary glands to the skin of the host. In this study, the salivary nitrophorin of Cimex lectularius was purified by DEAE chromatography and reverse-phase high-performance liquid chromatography. The purified nitrophorin had a molecular mass of 32.9 kDa. The DEAE-purified hemoprotein was able to bind NO, and this binding shifted the absorption maximum from 388 nm to 438 nm. The ratio of heme to apoprotein was estimated to be of 1:1. A cDNA clone of 1079 base pairs was sequenced and was found to code for a protein with a molecular mass of 31.7 kDa. The clone sequence was in agreement with the internal peptide sequences obtained from the purified protein. Sequencing of the isolated clone indicates high similarity to several inositol phosphatases; however, no significant similarities emerged when the sequence of C. lectularius nitrophorin was compared with that of R. prolixus nitrophorin, the only other nitrophorin known in insect saliva. Because C. lectularius and R. prolixus belong to two different families of Hemiptera that evolved independently to blood feeding, a case is made for the convergent evolution of these two insect nitrophorins.
温带臭虫和南美锥蝽的唾液中含有一氧化氮（NO），这可能有助于它们通过促进血管舒张和抑制血小板聚集来吸食脊椎动物宿主的血液。唾液中的NO与血红素蛋白（嗜硝蛋白）相关，这些蛋白将NO从昆虫唾液腺储存并运输到宿主皮肤。在本研究中，通过DEAE柱层析和反相高效液相色谱法纯化了温带臭虫的唾液嗜硝蛋白。纯化后的嗜硝蛋白分子量为32.9 kDa。经DEAE纯化的血红素蛋白能够结合NO，这种结合使吸收峰最大值从388 nm移至438 nm。血红素与脱辅基蛋白的比例估计为1:1。对一个1079个碱基对的cDNA克隆进行了测序，发现其编码的蛋白质分子量为31.7 kDa。克隆序列与从纯化蛋白获得的内部肽序列一致。对分离克隆的测序表明它与几种肌醇磷酸酶高度相似；然而，将温带臭虫嗜硝蛋白的序列与南美锥蝽嗜硝蛋白（昆虫唾液中已知的另一种嗜硝蛋白）的序列进行比较时，未发现明显的相似性。由于温带臭虫和南美锥蝽属于半翅目两个不同的科，它们独立进化为吸食血液，因此这两种昆虫嗜硝蛋白存在趋同进化的情况。
