Anomeric specificity

The sialidases cleave a-glycosidically linked sialic acid residues (Gottschalk 1958, Kuhn and Brossmer 1958). The sialic acids occurring in nature are found in the a-glycosidic conformation (see chapter B) with the exception of CMP-Neu5Ac which is a -glycoside (Haverkamp et al 1979 b) and which is not a substrate for sialidases. 

The initial demonstration of the a-anomeric specificity was made with IPNeu5AcLac (Kuhn and Brossmer 1958) with influenza and mumps virus sialidases. The preparation of synthetic p-glycosides of sialic acid allowed this specificity to be tested and verified for several viral and bacterial sialidases (Meindl and Tuppy 1965, Faillard et al 1966, Kuhn et al 1966). A further analysis was carried out on synthetic a-N- and a-S-glycosides of Neu5Ac, which proved not to be substrates for viral and bacterial sialidases (Khorlin et al 1970). Subsequent studies with V. cholerae sialidase and 4-nitrophenyl-a-Neu5Ac, however, showed low but significant release by the enzyme (Eschenfelder 1979). 

The nature of the cleavage mechanism has been studied using n.m.r.-spectroscopy leading to the proposal that the a-glycoside is cleaved to yield a-Neu5Ac which then leaves the active site of the sialidase molecule and mutarotates in water to give over 90% of the p-anomer (Holmquist and Ostman 1975, Friebolin et al 1980). 

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The question of a correlation of anomeric specificity of glycosidases with their susceptibility to aldonolactone inhibition was addressed by Reese and coworkers in a comparative study with six fungal a-D-glucosidases and... 

Often, the sweetness of simple sugars is reported in the literature without any indication of anomeric specification, although the values recorded in some cases refer to an equilibrated solution. In other instances, they refer to some unstated, partially mutarotated solution. 

REARRANGEMENTS ANOMERIC SPECIFICITY VALENCE TAUTOMERISM Teeth,... 

Use of locked substrates to determine the anomeric specificity of phosphofructokinase... 

The anomeric specificities of a number of glycolytic enzymes have been determined by using the reduced triphosphopyridine nucleotide (TPN)-coupled rate of oxidation with glucose-6- phosphate dehydrogenase, or by the enzyme glucose oxidase, which is also specific for the /3-anomer (106). 

By analysis of the products with glucose oxidase, it was shown that the anomeric composition of the glucose liberated from glucose-6-phos-phate by the enzymes acid or alkaline phosphatase or by glucose-6-phosphatase from rat liver was essentially the same as that of the substrate, thus indicating a lack of anomeric specificity for these enzymes also (106). 

Figure 11. Anomeric specificities of glucose-metabolizing enzymes (106)...

Anomerization of Glucose-6-Phosphate and Anomeric Specificity of Related Enzymes, J. Biol. Chem. (1965) 240, 561. 

Search enzyme databases for information to construct a database of glucosidases (EC 3.2.1.x) with retrievable fields on substrate (anomeric) specificity, catalytic mechanism (stereochemical, e.g., inversion versus retention) and kinetic constants (e.g., Km and V). 

The numerical values of the time constants summarized in Table 1 confirm that there is no particular time for significant mutarotation to take place in rapid on-line analyses. If glucose uptake is anomerically specific, as has been shown by Benthin et al. [23], analytical results obtained with a glucose oxidase method must be corrected accordingly. The same holds true for analyses of rapid biological transients and for any spiking method (if the spiking solution happens to be freshly prepared). 

Lectins differ markedly with respect to their anomeric specificity. Some, such as con A (Refs. 168, 169, and 197), the lectins from Ban-... 

Consistent with this explanation for anomeric specificity, mannose-phosphate isomerase (the substrate for which is the C-2 epimer of glucose 6-phosphate) uses the /3-anomer of substrate (Eq. (20)] ... 

Butler, W. Serif, G.S. Fucokinase, its anomeric specificity and mechanism of phosphate group transfer. Biochim. Biophys. Acta, 829, 238-243 (1985)... 

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