Publisher Summary This chapter discusses the procedures employed for the analysis of the sugar components of glycoproteins. Most of the methods used for the estimation of the monosaccharides present in glycoproteins are colorimetric in nature. Because of the relatively low specificity of some of these color reactions, it is often important to apply them only after appropriate separation of the constituents. In many cases complete identification, preferably by chromatographic means, of all the sugar and amino acid constituents of a glycoprotein should precede any colorimetric analysis so that potentially interfering substances may be taken into account. The hydrolytic release of the monosaccharides is also considered in the chapter. The optimal conditions of acid hydrolysis for the monosaccharides vary substantially because of differences both in the stability of their glycosidic bonds and in their susceptibility to destruction during the hydrolysis. One of the prerequisites for an accurate analysis of the monosaccharide components of a polymer is finding hydrolysis conditions under which all of a given sugar is released and yet is not significantly destroyed.

[1] Analysis of sugars found in glycoproteins

Physiological functions of mineral micronutrients (Cu, Zn, Mn, Fe, Ni, Mo, B, Cl).

Objective: To determine whether extended transthoracic esophagectomy for adenocarcinoma of the mid/distal esophagus improves long-term survival. Background: A randomized trial was performed to compare surgical techniques. Complete 5-year survival data are now available. Methods: A total of 220 patients with adenocarcinoma of the distal esophagus (type I) or gastric cardia involving the distal esophagus (type II) were randomly assigned to limited transhiatal esophagectomy or to extended transthoracic esophagectomy with en bloc lymphadenectomy. Patients with peroperatively irresectable/incurable cancer were excluded from this analysis (n = 15). A total of 95 patients underwent transhiatal esophagectomy and 110 patients underwent transthoracic esophagectomy. Results: After transhiatal and transthoracic resection, 5-year survival was 34% and 36%, respectively (P = 0.71, per protocol analysis). In a subgroup analysis, based on the location of the primary tumor according to the resection specimen, no overall survival benefit for either surgical approach was seen in 115 patients with a type II tumor (P = 0.81). In 90 patients with a type I tumor, a survival benefit of 14% was seen with the transthoracic approach (51% vs. 37%, P = 0.33). There was evidence that the treatment effect differed depending on the number of positive lymph nodes in the resection specimen (test for interaction P = 0.06). In patients (n = 55) without positive nodes locoregional disease-free survival after transhiatal esophagectomy was comparable to that after transthoracic esophagectomy (86% and 89%, respectively). The same was true for patients (n = 46) with more than 8 positive nodes (0% in both groups). Patients (n = 104) with 1 to 8 positive lymph nodes in the resection specimen showed a 5-year locoregional disease-free survival advantage if operated via the transthoracic route (23% vs. 64%, P = 0.02). Conclusion: There is no significant overall survival benefit for either approach. However, compared with limited transhiatal resection extended transthoracic esophagectomy for type I esophageal adenocarcinoma shows an ongoing trend towards better 5-year survival. Moreover, patients with a limited number of positive lymph nodes in the resection specimen seem to benefit from an extended transthoracic esophagectomy.

Extended transthoracic resection compared with limited transhiatal resection for adenocarcinoma of the mid/distal esophagus: five-year survival of a randomized clinical trial.

Analog approaches to the structure of the transition state in enzyme reactions

Publisher Summary This chapter discusses the results of the studies that permit some generalizations on the catalytic mechanism of glycoside hydrolases from widely differing sources and with different sugar and aglycon specificities and that have become available over the past 15 years. The strong inhibition of glycosidases by aldonolactones was first mentioned in 1940 by Japanese workers who studied β- D -glucosidases from Aspergillus (Taka-diastase) and almonds. Even though both of these groups of compounds are derived from normal substrates by only a minor modification of the glycon moiety, they are discussed together with pseudosubstrates because their reactions with glycosidases show, in many cases, unusual kinetic features. The information relevant to the mechanism of an enzyme-catalyzed reaction can, in general, only be obtained from irreversible inhibitors that react specifically at the active site, and thereby inactivate the enzyme. In many cases, inhibition studies were not carried out to obtain information on the reaction mechanism, but for other purposes. Thus, only inhibitors were tested that were considered suitable for the particular project, for example, studies on the biological function of the enzyme where glycosylamines and aldonolactones are unsuitable.

Glycoside Hydrolases: Mechanistic Information from Studies with Reversible and Irreversible Inhibitors

THE discovery of an enzyme decomposing glucuronide in the rumen of the sheep1 has been followed by the detection of similar enzymes in the large intestine of the horse2 and in locust crop liquor3. It seemed possible that such enzymes are concerned in the digestion of polysaccharides containing β-linked glucuronic acid residues, such as hemicellulose and hyaluronic acid, and a survey was therefore made of their occurrence in different parts of the alimentary tract in various species of animal. Typical results are shown in the accompanying table. It should be pointed out that these results are only of qualitative value, since the enzyme assays were carried out under conditions which are optimal for the sheep rumen enzyme1, but are not necessarily so for the enzymes from other sources. Moreover, in the rumen, omasum, caecum and colon, the enzymes may well be of microbial origin, as has been shown for the sheep rumen enzyme1, and therefore surrounded by membranes of varying toughness and permeability. A further factor which was not controlled was the diet of the animals, some of the material being obtained from the slaughter-house.

Glucuronide decomposition in the digestive tract.

The inhibition of glycosidases by aldonolactones.

CADMIUM has been reported to have a teratogenic effect in the golden hamster1, which is reversed by zinc. This prompts us to draw attention to our recent observation2 that zinc is an essential component of α-mannosidase. The active zinc–protein complex is readily dissociable at pH 5, the pH of optimum enzyme activity and the zinc ion can be displaced by cadmium, cobalt and other bivalent ions, with almost complete loss of enzyme activity (Fig. 1). These observations apply equally to the enzyme from rat epididymis3,4, jack bean meal5 and the limpet, Patella vulgata6.

α-Mannosidase as a Zinc-dependent Enzyme

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Mammalian glycosidases. 3. The intracellular localization of β-glucuronidase in different mammalian tissues

1. The previous study (Conchie, Gelman & Levvy, 1967b) of the specificity of beta-glucosidase, beta-galactosidase and beta-d-fucosidase in barley, limpet, almond emulsin and rat epididymis was extended to alpha-l-arabinosidase. 2. The inhibitory action of l-arabinono-(1-->5)-lactone was tested against all four types of enzyme, and alpha-l-arabinosidase was examined for inhibition by glucono-, galactono- and d-fucono-lactone. 3. In emulsin, the enzyme that hydrolyses beta-glucosides, beta-galactosides and beta-d-fucosides also hydrolyses alpha-l-arabinosides. Rat epididymis resembles emulsin except that, as already noted, it lacks beta-glucosidase activity. 4. In the limpet, alpha-l-arabinosidase activity is associated with the enzyme that hydrolyses beta-glucosides and beta-d-fucosides, and not with the separate beta-galactosidase. 5. The effects of the different lactones on the barley preparation suggest that alpha-l-arabinosidase activity is associated with the beta-galactosidase rather than with the enzyme that hydrolyses beta-glucosides and beta-d-fucosides. Fractionation and heat-inactivation experiments indicate that there is also a separate alpha-l-arabinosidase in the preparation.

/pdf/inhibition-of-glycosidases-by-aldonolactones-of-1yd7zjcvay.pdf

G. A. Levvy

Papers

Glucuronide decomposition in the digestive tract.

The inhibition of glycosidases by aldonolactones.

α-Mannosidase as a Zinc-dependent Enzyme

Mammalian glycosidases. 3. The intracellular localization of β-glucuronidase in different mammalian tissues

Inhibition of glycosidases by aldonolactones of corresponding configuration. The specificity of α-l-arabinosidase