Glucosidases 2-acetamido-2-deoxy

Thioamides 226 and 227, resulting from replacement of the amide carbonyl by thiocarbonyl in p-nitrophenyl 2-acelamido-2-deoxy-/3-D-gluco-and galacto-pyranosides, were shown to inhibit 2-acetamido-deoxy-/i-i> glucosidase from Turbatrix aceti.174 In contrast, the related p-nitrophenyl thioglycosides exhibited almost no inhibitory effect. In the light of the recent results of Knapp and co-workers,386 using the 4-methylumbelliferyl de-... 

Endo-2-acetamido-2-deoxy-)3-D-glucosidase has been used in structural studies of glycopeptides.30 The enzyme cleaves the linkage between the two 2-amino-2-deoxyglucose residues that constitute the chitobiose residue linked to L-asparagine in glycoproteins containing... 

A somewhat different procedure was needed for purifying the limpet enzyme to the same extent.48 The activity of a-D-mannosidase from this source was rapidly destroyed by pyridine. Selective inactivation of 2-acetamido-2-deoxy-/3-D-glucosidase was, therefore, effected by warming the preparation in 60% ethanol. /3-D-Galacto-sidase was removed in the course of fractionation. 

The first evidence for the presence of an a-D-mannosyl link in ovalbumin glycopeptides was provided by the action of almond emulsin,101,102 although the absence of /3-D-mannosidase from the enzyme preparation was not confirmed until later.103 The presence of 2-acetamido-2-deoxy-/M>glucosidase in emulsin left doubt as to the terminal position of all of the D-mannose released. 

When the ovalbumin was incubated with purified, jack-bean a-D-mannosidase, at least two molecules of D-mannose per molecule were released, suggesting that these residues are a-D-linked in a terminal position. Two glycopeptides having different contents of hexosamine were subjected to the action of purified 2-acetamido-2-deoxy-/ -D-glucosidase, and, in each case, two hexosamine residues per molecule were either inaccessible, or resistant to attack by the enzyme. 

Results of an experiment with an oligosaccharide free from amino acid were less conclusive, but were not incompatible with the structure shown. The oligosaccharide was prepared from a separated glycoprotein fraction having a D-mannose hexosamine ratio of 5 3. a-D-Mannosidase and 2-acetamido-2-deoxy-/3-D-glucosidase were used alternately. Initially, a-D-mannosidase removed about 1.5 D-mannose residues per molecule. Subsequent treatment of the residual oligosaccharide with 2-acetamido-2-deoxy-/3-D-glucosidase released rather less than one proportion of hexosamine residue, and then another 1.5 residues of D-mannose became open to attack by a-D-mannosidase. 

R. Montgomery and his colleagues108 fractionated, on Dowex 50, the aspartamidoglycan from ovalbumin. The five components obtained were each subjected to exhaustive hydrolysis with a-D-man-nosidase and 2-acetamido-2-deoxy-/3-D-glucosidase, used separately. The results are shown in Table X. One way in which to explain these results would be to change the position of the extra hexosamine residue in 1, to give the alternative structure 2. 

After removal of all of the D-mannose, one more hexosamine residue could be hydrolyzed off by 2-acetamido-2-deoxy-/3-D-glucosidase, indicating that this residue, also, is /3-D-linked.73... 

A number of other proteins are now known to exhibit heterogeneity with respect to their carbohydrate content these include pig pancreatic ribonuclease,9 rabbit19 and human109-238 -yG immunoglobulin, ceruloplasmin,239 2-acetamido-2-deoxy-/3-D-glucosidase,240 and the blood-group substances from ovarian cysts.145,241... 

Release of 2-Acetamido-2-deoxy-D-glucose from Glycoproteins and Glycopeptides (GP) by Use of 2-Acetamido-2-deoxy-/3-D-glucosidase... 

As a result of the various acidic and enzymic degradative studies on chitin, there can be little doubt that the polysaccharide is a homogeneous polymer composed of 2-acetamido-2-deoxy-D-glucose residues. Moreover, the specificity of chitinases as 2-acetamido-2-deoxy-/3-D-glucosidases confirms the /3-d nature of the glycosidic linkages. 

Isolated specific cell-surface components of rat hepatocytes involved in intracellular adhesion do not appear to be receptors for either fibronectin or heparin. The endocytosis of human urine o -D-2-acetamido-2-deoxy-glucosidase is mediated by at least three different cell-surface receptors on rat hepatocytes, involving the recognition of D-galactosyl, D-mannosyl 6-phosphate, and 2-acetamido-2- deoxy-D-glucosyl residues. ... 

The characteristics of bovine mammary gland 3-D-2-acetamido-2-deoxy-glucosidase have been studied. 

The effects of several hormones (progesterone, diethylstilbestrol) on chick oviduct j3-D-2-acetamido-2-deoxy-D-glucosidase isoenzymes have been studied. The total activity increased fourfold upon hormone withdrawal and upon treatment with progesterone alone or with progesterone plus diethylstilbestrol. 

Decreased binding by the lectins concanavalin A and wheat-germ agglutinin has been found for a number of acidic hydrolases ( 3-D-2-acetamido-2-deoxy-hexosidase, a-L-fucosidase, a- and jS-D-glucosidase, jS-D-galactosidase, and a-D-mannosidase) from skin fibroblasts of three unrelated patients with mucolipidosis II (see p. 423). 

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