性能描述

Most bacteria have a cell wall containing a special polymer called peptidoglycan. Over the cell membrane is a shift of peptidoglycan and other polymers including teichoic and teichuronic acids. This peptidoglycan gives a certain rigidity to the cell wall and gives the cell mechanical strength.
The bacterial cell wall is a unique biopolymer, it contains both D- and L-amino acids. Its basic structure is a carbohydrate backbone of alternating units of N-acetyl glucosamine and N-acetyl muramic acid. The N-acetyl muramic acid residues are cross-linked with oligopeptides. The terminal peptide is D-alanine although other amino acids are present as D- isomers. This is the only known biological molecule that contains D-amino acids and it is the target of numerous antibacterial antibiotics e.g. pencillin. Penicicllin inhibits the enzymes transpeptidase and carboxypeptidase, which are responsible for the building of peptidoglycan. Lysozyme, present in the tears liquid, is able to split the peptidoglycan between the N-acetyl glucosamine and N-acetyl muramic. The cell wall of Gram-positive bacteria is largely made up of pepidoglycan. There may be up to 40 layers of this polymer, conferring enormous mechanical strength on the cell wall. [3]
The primary immune recognition is based on structures common among invading pathogens. Surface molecules, such as lipopolysaccharide (LPS), peptidoglycan and peptidoglycan recognition protein (PGRP), are known to elicit immune reactions ranging from cytokine release to fever. [4-6]
Applications:
Used for the activity estimation of lytical enzymes (e.g. Lyticase). All peptidoglycan can be used for this purpose but Fluka 77145 can be used as chromogenic substrate for lytical enzymes. [1] It is recommended to use a peptidoglycan concentration of 0.15 – 3mg/l in water or buffer and measuring at 450 nm. The peptidoglycan can not be solubilized but it is possible to make a suspension. For the peptidoglycan dyed with remazol brilliant blue R (Fluka 77145) a possible working suspension is 3 mg/l glycin-buffer (0.2M, pH 10) which cam be measured at 595 nm. [7]
For the stimulation of lymphocytes: Peptidoglycan activates the Toll-like receptor 2 (TLR2), present in mammalian cells. Work as an antagonist of Poly (I:C).[2]

相关知识：

肽聚糖或称胞壁质（murein），存在于真细菌中的革兰氏阳性菌和革兰氏阴性菌的细胞壁中。肽聚糖的骨架是由两种糖衍生物：N-乙酰葡糖胺（GlcNAc）和N-乙酰胞壁酸（MurNAc）交替相连而形成的多糖链，这些链相互交联形成肽聚糖（如图1）。从每个N-乙酰胞壁酸引出一条寡肽链，与相邻多糖链上的N-乙酰胞壁酸相连（如图2），使两条平行的糖链横向相连构成网络，这样构成了整个细菌表面的细胞壁（如图3）。

图2: 大肠杆菌胞壁质的结构单元
一个细菌只被一个胞壁质分子所包围。胞壁质也可以由几层由多肽相互交联的网络组成。尤其革兰氏阳性菌的胞壁质具有很多层。并不是所有细菌都具有相同的胞壁质，它们在肽链的氨基酸组成上会有不同，但糖链骨架总是一样的。革兰氏阳性菌的组成区别更大一些。

图3: 细菌肽聚糖的示意图
这层胞壁质的壳可以帮助细菌的细胞质抵抗渗透造成的内压。如果胞壁质被溶菌酶等物质溶解，细菌将会破裂。在细菌生长时，胞壁质网需要增长，在其中就会形成较大的漏洞。胞壁质的结构单元由细胞质合成后输出。在细胞膜外的薄壁质网中的糖链和多肽链被特殊的水解酶局部断开，再由特殊的酶在其中插入从细胞新输出的结构单元。这个过程需要不同的酶精确协作。如果这种协作被破坏，则胞壁断裂后不能愈合，造成细菌破裂。某些抗生素就是通过这个机制杀菌的。