Muramidase, bacterial

Fi re 3.9 Schematic diagram of the structure of one domain of a bacterial muramidase, comprising 450 amino acid residues. The structure is built up from 27 a helices arranged in a two-layered ring. The ring has a large central hole, like a doughnut, with a diameter of about 30 A. 

Thunissen, A.-M., et al. Doughnut-shaped stmcture of a bacterial muramidase revealed by x-ray crystallography. Nature 367 750-753, 1994. 

Lysozyme (muramidase, mucopeptide JV-acetylmuramylhydrolase) is a widely distributed enzyme which lyses certain bacteria by hydrolysing the / (l-4)-linkage between muramic acid and N-acetylglucosamine of mucopolysaccharides of the bacterial cell wall. 

Lysozyme or muramidase, is an enzyme that catalyses the hydrolysis of the peptidoglycan layer of bacterial cell walls. The urinary excretion of lysozyme increases during urinary tract infections, proximal tubular damage, and excessive endogenous lysozyme synthesis that overwhelm the absorption capacity of the proximal tubule. 

Since there are objections (Rand-Meir ei o/., 1969) to the use of low molecular weight synthetic substrates for the estimation of muramidase activities (Lowe et al., 1967), inconvenient and relatively irapreckse assay methods employing derivatives of chitin or bacterial cell walls have to be used (Gibian, 1966). 

It is interesting to note that the C-0 of an amino sugar residue absorbed on subsite D would lie very close to amino acid residue 52 of muramidase (Blake el al., 1967b), so that it is perliaps not. surprising that acetyl and other substituents at C-6 of muramic acid moieties prevent the action of the enzyme (Work, 1967). However, an mdomuramidase from the fungus Chalaropsis sp. has been designated X,0-diacetylmuramidase since it attacks 6-0-acetylatcd X-acetyl-D-muramic acid residues in bacterial cell wall preparations Mitchell and Hash, 1969 Browder et al, 1905). 

Muramidase activities are widely distributed in materials of animal and microbial origin, and since the only likely substrates for these enzymes are bacterial cell walls (their action on native chitin is very slow-) (Berger and Reynolds, 1958), it seems reasonable to assume that they are concerned with the breakdown of these substances, or that they are vestigial. 

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