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Biomedical subjects

A Varki

Publications and source records attributed to A Varki.

At least 145 records · Page 8Linked to original sources
PubMed1986

Structure of a novel sialylated fucosyl lacto-N-norhexaosylceramide isolated from chronic myelogenous leukemia cells.

A novel sialylated fucosyl glycolipid, which is present at an elevated level in chronic myelogenous leukemia cells, was isolated. The structure of this fucoganglioside was elucidated by methylation analysis, fast atom bombardment-mass spectrometry, and enzymatic degradation, followed by reaction with anti-Lex, Gal beta 1----4 (Fuc alpha 1----3) GlcNAc beta 1----, monoclonal antibody. The structure of this ganglioside was found to be: (Formula: see text). This structure is unique in that a fucose is attached to the internal N-acetylglucosamine but not to the subterminal N-acetylglucosamine. Since this glycolipid is apparently absent in normal granulocytes or acute myelogenous leukemia cells, it can be a specific marker for chronic myelogenous leukemia cells. Based on the structures of this fucoganglioside and normal granulocyte glycolipids, a biosynthetic pathway of extension, sialylation, followed by fucosylation is proposed.

Antibodies, Monoclonal↗
PubMed1986

A sialic acid-specific O-acetylesterase in human erythrocytes: possible identity with esterase D, the genetic marker of retinoblastomas and Wilson disease.

The "nonspecific" esterases are a family of enzymes that were originally identified because of their reaction with synthetic O-acetyl ester substrates. While the electrophoretic polymorphisms of these enzymes have been extremely useful for genetic studies, their biological functions have remained completely unknown. Esterase D is characterized by its reactivity with 4-methylumbelliferyl acetate. This enzyme has recently been of particular interest because of its tight linkage to the putative recessive gene causing retinoblastomas, and to the recessive gene causing Wilson disease. We describe here the partial purification of a human erythrocyte esterase that appears to be highly specific for O-acetylated sialic acids. We next present evidence that suggests that esterase D is identical to this sialic acid-specific O-acetylesterase. First, both activities copurify from human erythrocyte lysates through several different purification steps, each of which use different principles of separation. Second, both activities show a remarkably similar profile of inhibition with a variety of different agents. Third, they both show a nearly identical heat-inactivation profile. This cytosolic sialic acid-specific O-acetylesterase appears to be involved in the "recycling" of O-acetylated sialic acid molecules. Thus, esterase D may be the first nonspecific esterase for which a specific biological role can be predicted.

Acetylesterase↗
PubMed1985

Structures of sialylated fucosyl polylactosaminoglycans isolated from chronic myelogenous leukemia cells.

Polylactosaminoglycans were isolated from human chronic myelogenous leukemia cells and their structures were elucidated. The lactosaminoglycan saccharides were isolated by hydrazinolysis and fractionated by QAE-Sephadex. The structures of fractionated oligosaccharides were analyzed by fast atom bombardment-mass spectrometry and methylation before and after treatment with specific exoglycosidases, such as alpha 2----3 specific neuraminidase. Based on these experiments, the structures of sialyl polylactosaminoglycans of chronic myelogenous leukemia cells were found to contain the following unique structure which is absent in normal mature granulocytes: (formula; see text) In addition to this, chronic myelogenous leukemia polylactosaminoglycans can be distinguished from normal granulocyte polylactosaminoglycans by the following characteristics. Leukemic polylactosaminoglycans are (a) shorter, (b) more highly sialylated and contain fully sialylated, tetrasialosyl polylactosaminoglycans, (c) are less fucosylated at C-3 of N-acetylglucosamine of polylactosaminyl side chains, and (d) contain a significant amount of sialyl Lex, NeuNAc alpha 2----3Gal beta 1----4(Fuc alpha 1----3)GlcNAc beta 1----3, structure. These results indicate that chronic myelogenous leukemia cells express unique polylactosaminoglycan structures which are distinct from normal mature granulocytes.

Amino Sugars↗
PubMed1985

The transport and utilization of acetyl coenzyme A by rat liver Golgi vesicles. O-acetylated sialic acids are a major product.

When intact rat liver Golgi vesicles were incubated with [acetyl-3H]acetyl coenzyme A, radioactivity was incorporated into the vesicles in a manner dependent upon temperature, time, protein, and acetyl-CoA concentration. The vesicles concentrated the label 121-fold relative to the medium within 20 min, suggesting an active transport mechanism operating in intact vesicles, and incorporated more than 50% of this label into acid-insoluble materials. This was supported by the finding that incorporation was markedly reduced by Triton X-100 at levels above its critical micellar concentration. While the intravesicular low molecular weight fraction was predominantly free acetate, acetate ions themselves were not permeant to the vesicles. Double-label experiments suggested that the transport process involved the entire acetyl-CoA molecule. This was further supported by the fact that coenzyme ASH, palmitoyl-CoA and butyryl-CoA were markedly inhibitory. Incorporation was optimal at 22 degrees C at pH 7.0, and was moderately stimulated by ATP. However, compounds known to abolish proton gradients or to inhibit the Golgi proton pump had no effect. The apparent Km for the utilization process was 0.61 microM with a Vmax of 21.3 pmol/mg of protein/min. Oligomycin and 4,4'-diisothiocyanostilbene-2,2'disulfonic acid were inhibitory, whereas CMP-NeuAc, UDP-GlcNAc, adenosine 3'-phosphate, 5'-phosphosulfate, atractylosides, tunicamycin, 2'5'-ADP, and 3',5'-ADP were not, showing that this transport process is distinct from other nucleotide transporters previously described in rat liver Golgi. 75-85% of the radioactivity incorporated was shown to be in O-acetylated sialic acids, by neuraminidase release, purification, and high pressure liquid chromatography. The majority of the neuraminidase-resistant radioactivity was released by alkaline hydroxylamine as [3H]acetylhydroxamate, but a significant fraction was resistant to this treatment. The nature of the non-sialic acid radioactivity remains unknown. The existence of this transport mechanism provides yet another level at which the O-acetylation of sialic acids could be regulated.

Acetyl Coenzyme A↗
PubMed1985

Metabolic labeling of sialic acids in tissue culture cell lines: methods to identify substituted and modified radioactive neuraminic acids.

The parent sialic acid N-acetylneuraminic acid can be modified or substituted in various ways, giving rise to a family of more than 25 compounds. The definitive identification of these compounds has previously required isolation of nanomole amounts for mass spectrometry or NMR. We have explored the possibility of using the known metabolic precursors of the sialic acids, particularly N-acetyl-[6-3H]mannosamine, to label and identify various forms of sialic acids in tissue culture cells. Firstly, we defined several variables that affect the labeling of sialic acids with N-acetyl-[6-3H]mannosamine. Secondly, we have devised a simple screening method to identify cell lines that synthesize substituted or modified sialic acids. We next demonstrate that it is possible to definitively identify the natures of the various labeled sialic acids without the use of mass spectrometry, even though they are present only in tracer amounts. The methods used include paper chromatography, analytical de-O-acetylation, periodate release of the 9-3H as [3H]formaldehyde (which is subsequently converted to a specific 3H-labeled chromophore), acylneuraminate pyruvate lyase treatment with identification of [3H]acylmannosamines, gas-liquid chromatography with radioactive detection, and two new high-pressure liquid chromatography methods utilizing the amine-adsorption:ion suppression and ion-pair principles. The use of an internal N-acetyl-[4-14C]neuraminic acid standard in each of these methods assures precision and accuracy. The combined use of these methods now allows the identification of radioactive tracer amounts of the various types of sialic acids in well-defined populations of tissue culture cells; it may also allow the identification of hitherto unknown forms of sialic acids.

Animals↗
PubMed1984

The release and purification of sialic acids from glycoconjugates: methods to minimize the loss and migration of O-acetyl groups.

The sialic acids can have O-acetyl esters at the 4, 7, 8, and 9 positions. Most methods for the detailed study of such molecules require their release from glycosidic linkage, followed by extensive purification. The currently used methods for release and purification of sialic acids allow a reasonable qualitative analysis of the diversity of sialic acids from a given biological source. However, for several reasons, quantitative assessment of the degree and type of O-acetylation is not possible with these methods. Previously known problems include the incomplete and nonrandom release of the different sialic acids by both enzymatic and chemical means, and extensive destruction of the O-acetyl esters (de-O-acetylation) during the release and purification. An additional problem, that migration of O-acetyl groups from the 7 or 8 positions to the 9 position can occur under the conditions of release and purification, particularly when the pH is above 6 or below 3.0, is demonstrated here. It is shown that the O-acetyl esters on free sialic acids are relatively more stable under acid conditions but more labile under basic conditions than similar esters on bound sialic acids. An analysis of the various steps of the conventional purification procedure showed that exposure to the basic anion-exchange resin is the critical step that results in de-O-acetylation and O-acetyl migration. Based upon these and other findings some new methods have been devised, and several modifications of the existing methods have been suggested, that allow the quantitative release and purification of sialic acids with minimal loss of O-acetyl groups. The migration of O-acetyl groups is also decreased by these modifications, but cannot be completely controlled.

Acetylation↗
PubMed1983

A neuraminidase from Streptococcus sanguis that can release O-acetylated sialic acids.

The naturally occurring sialic acids can have different types of N- and O-substitutions, resulting in more than 20 known isomers and compounds. Most methods for the detailed study of these various sialic acids require that the molecules be first released from their alpha-glycosidic linkage. When mild acid hydrolysis is used for this purpose, significant destruction of O-substituent groups occur. On the other hand, the presence of O-substituent groups renders the sialic acid molecule partially or completely resistant to the action of the currently known neuraminidase. To circumvent this problem, we searched for a neuraminidase whose activity is not affected by O-substitution. We reasoned that because Streptococcus sanguis from the human oral cavity is continually exposed to O-substituted sialic acids, its extracellular neuraminidase might not be blocked by O-substitution. We therefore purified this enzyme 3100-fold (56% yield) using ammonium sulfate precipitation, N-(p-aminophenyl)oxamic acid-agarose affinity chromatography, and chromatography on quaternary aminoethyl (QAE)-Sephadex, sulfopropyl (SP)-Sephadex, and Sephacryl S-200. The purified preparation is free of other significant glycosidase activities and proteolytic activities. It is capable of quantitatively releasing all the O-acetylated sialic acids that we studied with the single exception of the 4-O-acetylated sialic acid of equine submaxillary mucin. The activity of the enzyme is also not restricted by the type pf sialic acid linkage or the nature of the underlying oligosaccharide. However, it has maximal activity on gangliosides only in the presence of detergents. The general properties of this enzyme are described and its substrate specificities are contrasted with those of the commonly used neuraminidase from Vibrio cholerae.

Animals↗
PubMed1983

Demonstration of the enzymatic mechanisms of alpha-N-acetyl-D-glucosamine-1-phosphodiester N-acetylglucosaminidase (formerly called alpha-N-acetylglucosaminylphosphodiesterase) and lysosomal alpha-N-acetylglucosaminidase.

An enzyme that is capable of removing the outer N-acetylglucosamine residues from phosphodiesters present on the high-mannose-type oligosaccharides of newly synthesized lysosomal enzymes has been described. This enzyme has been called an alpha-N-acetylglucosaminylphosphodiesterase, based upon its substrate specificity and on inhibitor studies. In this study it is demonstrated by the 18O enrichment method that the enzyme cleaves the C-O bond rather than the O-P bond, and therefore acts by a glycosidase type of mechanism. In addition, the enzyme has no significant activity toward alpha-N-acetylglucosamine 1-phosphate, and therefore requires an underlying phosphodiester for activity. In accordance with the IUB recommendations for enzyme nomenclature, it is therefore suggested that the enzyme be renamed alpha-N-acetyl-D-glucosamine-1-phosphodiester N-acetylglucosaminidase (systematic name, 2-acet-amido-2-deoxy-alpha-D-glucose 1-phosphodiester acetamidodeoxyglucohydrolase). For convenience, the trivial name phosphodiester glycosidase is proposed. Lysosomal alpha-N-acetylglucosaminidase also has a glycosidase type of mechanism but it is active toward alpha-N-acetylglucosamine 1-phosphate as well as phosphodiesters with outer N-acetylglucosamine residues.

Acetylglucosaminidase↗
PubMed1983

The spectrum of anionic oligosaccharides released by endo-beta-N-acetylglucosaminidase H from glycoproteins. Structural studies and interactions with the phosphomannosyl receptor.

We have performed a detailed analysis of all the anionic oligosaccharides released by endo-beta-N-acetylglucosaminidase H from the whole cell glycoproteins of P388D1 mouse macrophage-like cells labeled for 14 h with [2-3H]mannose. The major anionic species consisted of phosphorylated high mannose-type oligosaccharides containing one or two phosphomonoesters or phosphodiesters in several different positions. In addition we identified hybrid-type molecules containing one, two, or three sialic acid residues. A subset of the latter molecules also contained phosphodiesters or phosphomonoesters on another branch of the same oligosaccharide. Unlike previously reported hybrid-type molecules, these do not have a "bisecting" N-acetylglucosamine residue on the beta-linked mannose. Some of these oligosaccharides contained an unidentified acid-labile group on the core N-acetylglucosamine or the beta-linked mannose. The glycoproteins secreted by these cells were greatly enriched in hybrid oligosaccharides containing one sialic acid and one phosphomonoester. The interaction of the isolated oligosaccharides with bovine liver phosphomannosyl receptor immobilized on Affigel was analyzed. Oligosaccharides with phosphomonoesters were the only species that interacted with high affinity with the receptor, and molecules with two phosphomonoesters showed the best binding. The location of the phosphomonoester on the oligosaccharide influenced the degree of interaction with the receptor. Removal of accessible nonphosphorylated mannose residues improved the binding in some cases. These findings indicate that the generation of the physiological phosphomannosyl ligand on lysosomal enzymes involves removal of the blocking N-acetylglucosamine residues, trimming of certain mannose residues, and correct positioning of the phosphate esters.

Acetylglucosaminidase↗
PubMed1983

The syndrome of idiopathic myelofibrosis. A clinicopathologic review with emphasis on the prognostic variables predicting survival.

We describe here a series of 88 consecutive patients with bone marrow fibrosis. Primary causes for the fibrosis were discovered in 26% of the cases shortly after the initial diagnosis. Pathology review of the remaining cases revealed an 8% incidence of "hairy cell leukemia" that had escaped detection originally. The remaining cases, characterized as having "unexplained bone marrow fibrosis" or "idiopathic myelofibrosis," are the subject of this study. The clinical and laboratory findings are compared to those reported in previous series of selected cases with similar features in which patients were diagnosed as having "agnogenic myeloid metaplasia," "myelosclerosis," or "myelofibrosis." A brief summary of the treatment modalities used, and the clinical course and outcome of these patients are also presented. There was a marked variability in the clinical severity of the disease and in the survival of these patients. A detailed statistical analysis of 40 variables at the time of initial diagnosis showed that the factors that best predicted a poor survival were unexplained fever, weight loss, night sweats, anemia and thrombocytopenia. On the other hand, the size of the spleen or of the liver, the degree of immaturity of the peripheral blood white cells, and the degree of fibrosis or cellularity in the bone marrow biopsy were of no detectable prognostic significance. These findings suggest that in patients with unexplained fibrosis of the bone marrow (the syndrome of idiopathic myelofibrosis) a poor prognosis is not a direct consequence of the marrow fibrosis or the associated extramedullary hematopoiesis, but rather is related to the presence and/or the severity of some unexplained primary marrow defect, which is also often associated with the nonspecific symptoms of a systemic illness.

Adolescent↗
PubMed1982

Steps in the phosphorylation of the high mannose oligosaccharides of lysosomal enzymes.

The phosphomannosyl recognition marker of acid hydrolases, which mediates their translocation to lysosomes, has been shown to be synthesized in two steps. First, N-acetylglucosamine 1-phosphate is transferred to an acceptor mannose by UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase, resulting in a phosphate group in diester linkage between the outer N-acetylglucosamine and the inner mannose. Next, an a-N-acetylglucosaminyl phosphodiesterase removes the N-acetylglucosamine, leaving the phosphate in monoester linkage with the underlying mannose residue. This exposed phosphomannosyl residue serves as the essential component of a recognition marker which leads to binding to high-affinity receptors and subsequent translocation to lysosomes. We propose that the first enzyme in this scheme, N-acetylglucosaminylphosphotransferase, catalyses the initial, determining step by which newly synthesized acid hydrolases are distinguished from other newly synthesized glycoproteins and thus are eventually targeted to lysosomes. The absence of this enzyme activity, as in inclusion-cell (I-cell) disease and pseudo-Hurler polydystrophy, precludes the receptor-mediated targeting of newly synthesized acid hydrolases to lysosomes. As a consequence, the enzymes are secreted into the extracellular milieu.

Animals↗
PubMed1982

Two clonal cell populations (mosaicism) in a 46,XY male with mucolipidosis II (I-cell disease)--an autosomal recessive disorder.

Cultured fibroblasts from a 46,XY male with an atypical form of mucolipidosis II (I-cell disease) had two distinct phenotypes. One population of these fibroblasts had the morphological and biochemical features characteristic of I-cell disease, while the remaining cells were indistinguishable from normal fibroblasts. Direct evidence that the patient was a mosaic, having two cell populations, was provided by the establishment of pure, stable clones of both wild type and I-cell fibroblasts from each of two biopsies obtained several months apart. Additionally, it was shown that the I-cell fibroblasts lacked UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosaminylphosphotransferase while the morphologically normal cells contained levels of this enzyme just below or at the lower end of the normal range.

Cells, Cultured↗
PubMed1982

Demonstration of the heterozygous state for I-cell disease and pseudo-Hurler polydystrophy by assay of N-acetylglucosaminylphosphotransferase in white blood cells and fibroblasts.

The biochemical abnormalities of I-cell disease (mucolipidosis II) and pseudo-Hurler polydystrophy (mucolipidosis III) can be explained by a deficiency of the enzyme UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. We demonstrate here that obligate heterozygotes for these autosomal recessive diseases have intermediate levels of this enzymatic activity in homogenates of peripheral blood white cells and in extracts from cultured fibroblasts. This finding provides further evidence that the enzyme deficiency is the primary genetic defect in these diseases. In addition, the previous observation that obligate heterozygotes for mucolipidosis III have elevations of total serum beta-hexosaminidase outside the range of normal was confirmed. In studies of three pedigrees of patients with mucolipidosis III, these techniques were used to score individuals at risk for the carrier state.

Cells, Cultured↗
PubMed1981

Purification and characterization of rat liver alpha-N-acetylglucosaminyl phosphodiesterase.

In an earlier report we described the identification of an alpha-N-acetylglucosaminyl phosphodiesterase that is capable of cleaving the outer phosphodiester-linked alpha-N-acetylglucosamine residues present on the high mannose oligosaccharides of newly synthesized lysosomal enzymes (Varki, A., and Kornfeld, S. (1980) J. Biol. Chem. 255, 8398-8401). We have now purified this enzyme 1800-fold with a 24% yield from rat liver, using subcellular fractionation, differential extraction with Triton X-10, DEAE-cellulose chromatography, heparin-Sepharose chromatography, concanavalin A-Sepharose affinity chromatography, and gel filtration on Sephacryl S-300. The purified preparation is free of lysosomal alpha-N-acetylglucosaminidase. The enzyme exhibited a single form on both the ion exchange and gel filtration steps. It has a broad pH optimum between 6.0-8.0 and is unaffected by divalent cations or reducing agents. The enzyme cleaves alpha-N-acetylglucosamine residues from five different locations on the high mannose oligosaccharide. In the case of molecules with one phosphodiester, the rate of cleavage is not affected by the size of the underlying oligosaccharide or the presence or absence of an asparagine-linked peptide. Molecules with two phosphodiesters are cleaved in a nonrandom manner. The enzyme has no activity toward p-nitrophenyl-alpha-N-acetylglucosamine but is capable of cleaving phosphodiester-linked N-acetylglucosamine in molecules such as UDP-N-acetylglucosamine, indicating that it can only hydrolyze N-acetylglucosamine residues that are alpha-linked to a phosphate group.

Animals↗
PubMed1981

Fibroblasts from patients with I-cell disease and pseudo-Hurler polydystrophy are deficient in uridine 5'-diphosphate-N-acetylglucosamine: glycoprotein N-acetylglucosaminylphosphotransferase activity.

Newly synthesized acid hydrolases, destined for transport to lysosomes, acquire a phosphomannosyl targeting signal by the transfer of N-acetylglucosamine 1-phosphate from uridine 5'-diphosphate (UDP)-N-acetylglucosamine to a mannose residue of the acid hydrolase followed by removal of the outer, phosphodiester-linked N-acetylglucosamine to expose 6-phosphomannose. This study demonstrates that fibroblasts from patients with the lysosomal enzyme storage diseases, I-cell disease (mucolipidosis II) and pseudo-Hurler polydystrophy (mucolipidosis III), are severely deficient in UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminylphosphotransferase, the first enzyme of the sequence. The N-acetylglucosaminylphosphotransferase activity (assayed using endogenous acceptors) in cultures from six normal subjects ranged from 0.67 to 1.46 pmol N-acetylglucosamine-1-phosphate transferred/mg protein per h, whereas five pseudo-Hurler polydystrophy and five I-cell disease cultures transferred less than 0.02 pmol/mg protein per h. The activity in five other pseudo-Hurler cultures ranged from 0.02 to 0.27 pmol transferred/mg protein per h. The activity of alpha-N-acetylglucosaminyl phosphodiesterase, the enzyme responsible for phosphomonoester exposure, is normal or elevated in cultured fibroblasts from both I-cell disease and pseudo-Hurler polydystrophy patients. The deficiency of UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminylphosphotransferase explains the biochemical abnormalities previously observed in I-cell disease and pseudo-Hurler polydystrophy.

Cells, Cultured↗
PubMed1980

Structural studies of phosphorylated high mannose-type oligosaccharides.

Phosphomannosyl residues on acid hydrolases serve as recognition markers which target these enzymes to lysosomes. We have found that the oligosaccharide units of newly synthesized beta-glucuronidase contain phosphate residues in diester linkage between mannose and alpha-linked N-acetylglucosamine residues (Tabas, I., and Kornfeld, S. (1980) J. Biol. Chem. 255, 6633--6639). To obtain larger amounts of these molecules for structural studies, total cellular glycopeptides were isolated from [2-3H]mannose-labeled mouse lymphoma cells, and the phosphorylated oligosaccharides were released by endo-beta-N-acetylglucosaminidase CII and H and isolated by gel filtration and ion exchange chromatography. The fractions were characterized by alpha-mannosidase digestion before and after removal of the phosphate residues and by acetolysis. We also determined whether the phosphate was present as a phosphomonoester or as a diester. The phosphorylated oligosaccharides consisted of a family or related molecules, all of which contained a high mannose-type oligosaccharide core. The major class consisted of isomers containing a single phosphate in diester linkage to 1 of 3 mannose residues of the underlying oligosaccharide. The second class contained isomers with two phosphodiester groups located at five different positions of the oligosaccharide. In both of these classes, the phosphodiester group could be converted to a phosphomonoester by pig liver alpha-N-acetylglucosaminidase, indicating that the cover is alpha-linked N-acetylglucosamine. The third class was similar to the second except that the 2 phosphate residues were present as monoester groups. The last class contained molecules with a single phosphomonoester group. These molecules differed from those with single phosphodiester groups in that the core oligosaccharides were smaller. This is consistent with their being more mature species which have undergone partial processing. These data demonstrate that phosphorylation can occur at 5 separate mannose residues on the high mannose-type oligosaccharides. Individual molecules can have 1, 2, and perhaps even 3 phosphate residues. The majority of the newly synthesized phosphorylated oligosaccharides contain phosphate groups in diester linkage.

Acetylglucosaminidase↗
PubMed1980

Identification of a rat liver alpha-N-acetylglucosaminyl phosphodiesterase capable of removing "blocking" alpha-N-acetylglucosamine residues from phosphorylated high mannose oligosaccharides of lysosomal enzymes.

We recently reported that the high mannose-type oligosaccharides of the biosynthetic intermediates of beta-glucuronidase contain phosphate groups in diester linkage between mannose residues and outer alpha-linked N-acetylglucosamine residues (Tabas, I., and Kornfeld, S. (1980) J. Biol. Chem. 255, 6633-6639). We now describe an alpha-N-acetylglucosaminyl phosphodiesterase from rat liver that is capable of removing the N-acetyl-glucosamine residues, leaving phosphomonoester groups on the high mannose oligosaccharide units. This activity is greatly enriched in smooth membrane preparations. It can be distinguished from a lysosomal alpha-N-acetylglucosaminidase by several criteria, including subcellular localization and differential inhibition by amino sugars. In addition, human fibroblasts with mutations which lead to a deficiency of the lysosomal activity have normal levels of the alpha-N-acetylglucosaminyl phosphodiesterase. This enzyme may be involved in the "unmasking" of the phosphomannosyl recognition marker on newly synthesized acid hydrolases which could then direct the targeting of these enzymes to lysosomes.

Acetylglucosaminidase↗