Tellam R L, Eisemann C
CSIRO Tropical Agriculture, Private Mail Bag 3, 4068 Queensland, Indooroopilly, Australia.
Insect Biochem Mol Biol. 2000 Dec;30(12):1189-201. doi: 10.1016/s0965-1748(00)00097-7.
The gut of most insects is lined with a peritrophic matrix that facilitates the digestive process and protects insects from invasion by micro-organisms and parasites. It is widely accepted that the matrix is composed of chitin, proteins and proteoglycans. Here we critically re-examine the chitin content of the typical type 2 peritrophic matrix from the larvae of the fly Lucilia cuprina using a range of techniques. Many of the histochemical and biochemical techniques indicate the presence of chitin, although they are often adversely influenced by the presence of highly glycosylated proteins, a principal component of the matrix. The alkali-stable fraction, which is used as an indicator of the maximum chitin content in a biological sample, is only 7.2% of the weight of the matrix. Larvae fed on the potent chitin synthase inhibitor polyoxin D or the chitin-binding agent Calcofluor White, showed strong concentration-dependent inhibition of larval weight and survival but no discernible effects on the matrix structure. A bacterial endochitinase fed to larvae had no effect on larval growth and no observable effect in vitro on the structure of isolated peritrophic matrix. RT-PCR did not detect a chitin synthase mRNA in cardia, the tissue from which PM originates. It is concluded that chitin is a minor structural component of the type 2 peritrophic matrix of this insect.
大多数昆虫的肠道内衬有一层围食膜，它有助于消化过程，并保护昆虫免受微生物和寄生虫的侵袭。人们普遍认为，围食膜由几丁质、蛋白质和蛋白聚糖组成。在这里，我们使用一系列技术对绿蝇幼虫典型的2型围食膜中的几丁质含量进行了批判性的重新审视。许多组织化学和生化技术表明存在几丁质，尽管它们常常受到围食膜主要成分之一的高度糖基化蛋白质的不利影响。用作生物样品中几丁质最大含量指标的碱稳定部分仅占围食膜重量的7.2%。用强效几丁质合酶抑制剂多氧霉素D或几丁质结合剂荧光增白剂喂养的幼虫，显示出对幼虫体重和存活率有强烈的浓度依赖性抑制，但对围食膜结构没有明显影响。喂给幼虫的一种细菌内切几丁质酶对幼虫生长没有影响，在体外对分离的围食膜结构也没有可观察到的影响。逆转录聚合酶链反应未在围食膜起源的组织贲门中检测到几丁质合酶mRNA。结论是，几丁质是这种昆虫2型围食膜的次要结构成分。
