ENDO-N-ACETYL-BETA-D-GLUCOSAMINIDASES AND THEIR POTENTIAL SUBSTRATES - STRUCTURE FUNCTION RELATIONSHIPS/

Endo-N-acetyl-beta-D-glucosaminidases (ENGases) have been defined as t he enzymes that hydrolyse the glycosidic bond between an N-acetyl-beta -D-glucosamine residue and the adjacent (partner) monosaccharide withi n an oligosaccharide chain. Three types of enzymes have been distingui shed according to this definition: ENGases acting on murein (type I), those acting on chitin (type II) and, finally, those acting on N-glyca ns (type III). Considering that N-acetylmuramic acid is a derivative o f N-acetylglucosamine (3-O-substituted by a lactyl group), only ENGase s acting between two N-acetylglucosamine residues are actually known d espite the fact that other possibilities of partner monosaccharides fo r N-acetyl-beta-D-glucosamine are reported. Similarities in the amino acid sequences were found to occur only between chitin-ENGases and N-g lycan-ENGases, but the substrate specificities of these two types of e nzymes are different. However, it is possible that certain enzymes are able to cleave more than one type of substrate, and this could in par ticular explain why the N-glycan-ENGases are largely produced by bacte ria in which no potential substrate for this type of enzymes was ident ified. Further study in this area is expected.