Huber M, Cabib E, Miller L H
Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
Proc Natl Acad Sci U S A. 1991 Apr 1;88(7):2807-10. doi: 10.1073/pnas.88.7.2807.
Malaria parasites (ookinetes) appear to digest the peritrophic membrane in the mosquito midgut during penetration. Previous studies demonstrated that lectins specific for N-acetylglucosamine bind to the peritrophic membrane and proposed that the membrane contains chitin [Rudin, W. & Hecker, H. (1989) Parasitol. Res. 75, 268-279]. In the present study, we show that the peritrophic membrane is digested by Serratia marcescens chitinase (EC 3.2.1.14), leading to the release of N-acetylglucosamine and fragmentation of the membrane. We also report the presence of a malaria parasite chitinase that digests 4-methylumbelliferyl chitotriose. The enzyme is not detectable until 15 hr after zygote formation, the time required for maturation of the parasite from a zygote to an ookinete, the invasive form of the parasite. At 20 hr, the enzyme begins to appear in the culture supernatant. The chitinase extracted from the parasite and found in the culture supernatant consists of a major band and two minor bands of activity on native polyacrylamide gel electrophoresis. The presence of chitin in the peritrophic membrane, the disruption of the peritrophic membrane during invasion, and the presence of chitinase in ookinetes suggest that the chitinase in ookinetes is used in the penetration of the peritrophic membrane.
疟原虫（动合子）在穿透过程中似乎会消化蚊子中肠的围食膜。先前的研究表明，对N-乙酰葡糖胺具有特异性的凝集素会与围食膜结合，并提出该膜含有几丁质[鲁丁，W. & 赫克，H.（1989年）《寄生虫学研究》75卷，268 - 279页]。在本研究中，我们发现粘质沙雷氏菌几丁质酶（EC 3.2.1.14）可消化围食膜，导致N-乙酰葡糖胺释放以及膜的碎片化。我们还报告了疟原虫几丁质酶的存在，该酶可消化4-甲基伞形酮基壳三糖。直到合子形成后15小时才能检测到这种酶，这段时间是疟原虫从合子发育为动合子（即寄生虫的侵袭形式）所需的成熟时间。在20小时时，该酶开始出现在培养上清液中。从寄生虫中提取并在培养上清液中发现的几丁质酶在天然聚丙烯酰胺凝胶电泳上由一条主要条带和两条次要条带的活性组成。围食膜中存在几丁质、侵袭过程中围食膜的破坏以及动合子中存在几丁质酶表明，动合子中的几丁质酶用于穿透围食膜。
