Polysaccharide-enzyme interaction

The idea that polysaccharide-polysaccharidase interaction could be treated simply as the sum of the interactions of various subsites is intuitively attractive. Hiromi first tackled the algebra, but made the assumption, now known to be implausible, that the microscopic rate constant for bond cleavage in the ES complex was independent of subsite occupancy. This is very unlikely for enzymes in general terms, since it is now accepted that they exploit interactions with the substrate remote from the site of bond cleavage to lower the free energy for the catalysed reaction (the Circe effect, Section 5.4.5.3). The Hiromi assumption was shown to be incorrect by direct experiments with an endoxylanase. A better fit to experimental data was obtained if the subsite affinities were calculated for the first irreversible transition state i.e. on kcat/A)n and cleavage patterns of oligosaccharides), but careful analysis in some systems indicated that even this approximation failed. ... 

Cell components or metabolites capable of recognizing individual and specific molecules can be used as the sensory elements in molecular sensors [11]. The sensors may be enzymes, sequences of nucleic acids (RNA or DNA), antibodies, polysaccharides, or other reporter molecules. Antibodies, specific for a microorganism used in the biotreatment, can be coupled to fluorochromes to increase sensitivity of detection. Such antibodies are useful in monitoring the fate of bacteria released into the environment for the treatment of a polluted site. Fluorescent or enzyme-linked immunoassays have been derived and can be used for a variety of contaminants, including pesticides and chlorinated polycyclic hydrocarbons. Enzymes specific for pollutants and attached to matrices detecting interactions between enzyme and pollutant are used in online biosensors of water and gas biotreatment [20,21]. 

Heparin has been found to bind a large number of proteins (Table 3). The biological activity of heparin and related polysaccharides is usually ascribed to their interaction with heparin-binding proteins. These proteins can be classified into classes including (1) enzymes, (2) protease inhibitors, (3) lipoproteins, (4) growth factors, (5) chemokines, (6) selectins, (7) extracellular matrix proteins, (8) receptor proteins, (9) viral coat proteins, (10) nuclear proteins, and (11) other proteins (1). Many heparin-binding proteins are enzymes and enzyme inhibitors. For example, proteases in the coagulation cascade, such as factors Ha, IXa, Xa, Xlla, and Villa, are heparin-... 

A good example of this interaction in catalysis is the hydrolysis of the bacterial cell wall polysaccharide by lysozyme. This enzyme contains two carboxylic gronps at its active site and, in active enzyme one must be in dissociated—COO, the other in the undissociated—COOH form. Therefore, the pK s of the two carboxylic groups ate different. This difference in dissociation constant is a consequence of the neighbouring amino acid residues and of the interactions between the functional groups in the microenvironment. 

---