Sialidase characteristics

The substrate-specificity studies described in this Subsection show striking similarities between the sialidases from various sources, but also characteristic differences with regard to the N- and O-substitu-tions of Neu, the sialic acid glvcosidic linkages, and the oligosaccharide, glycoprotein, or ganglioside nature of the substrates.55... 

The three-dimensional structure of TcTS was determined by crystallographic studies on a fully active TcTS mutant.145 147 It consists of two domains the N-terminal catalytic domain which forms a six-bladed [1 propeller, characteristic of microbial sialidases, connected through a long a helix to a C-terminal lectin-like domain which does not participate in the enzymatic reaction. The catalytic domain... 

The alkaline phosphatase of both human intestine and placenta are L-phenyl-alanine-sensitive and undergo uncompetitive inhibition to the same extent (nearly 80%) by 0.005 M L-phenylalanine. However, we have been able to find several distinguishing biochemical characteristics of the two enzymes (1) the anodic mobility of intestinal alkaline phosphatase remains unchanged after neuraminidase treatment, whereas the placental enzyme is sialidase-seusitive and hence the electrophoretic mobility on starch gel is considerably reduced by such treatment, (2) the Michaelis constant of placental alkaline phosphatase at a definite pH is appreciably higher than that of the intestinal enzyme (at pH 9.3 the Km values of placenta and intestine are 316 and 160 ixM, respectively), and (3) the pH optima (with 0.018 Af phenyl phosphate as substrate) of the two enzymes are different the values for intestinal and placental enzymes with 0.006 Af n-phenylalanine are 9.9 and 10.6, respectively, and the respective values in the presence of 0.005 Af L-phenylalanine are 10.2 and 11.1. Finally, contrary to the behavior of intestinal alkaline phosphatase, placental enzyme is completely heat stable (P19). 

A further aspect of the wide range of substrates for sialidases has been the analysis of these substrates. The determination of oligosaccharide chain structures has allowed precise study of sialidase specificity. A need for a spectrum of well defined substrates has developed as a prerequisite for the elucidation of sialidase specificity. The large body of data which has accumulated on the sialidases points to a number of characteristics general to sialidase action, and forms the basis of current knowledge about sialidases. 

Corfield, A. P., Wember, M., Schauer, R., and Rott, R., 1982, The specificity of viral sialidases The use of oligosaccharide substrates to probe enzyme characteristics and strain-specific differences, Eur. J. Biochem. 124 521-525. 

Deficient activity in lysosomal acid sialidase (a-neuraminidase) is the genetic defect underlying sialidosis. Sialic acid occurs at the nonreducing terminus of the carbohydrate chains of many glycoproteins and also as a characteristic component of gangliosides. However, there is no biochemical or enzymological... 

To date, little about the purification of sialidase from mammalian cells has been published. The membrane-bound sialidase must be solubilized before any of the usual purification procedures can be applied. The solubilized sialidase that has been purified probably is still associated with a small membrane fragment. The soluble enzyme can be readily concentrated by standard procedures. To determine the mechanism of action of the enzyme and its physical characteristics, it may eventually be necessary somehow to obtain sialidase in truly purified form. 

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