Isolation of beta-N-acetylhexosaminidase, beta-N-acetylglucosaminidase, and beta-N-acetylgalactosaminidase from calf brain

Biosynthesis and Biological Activity of Carbasugars

The first synthesis of carbasugars, compounds in which the ring oxygen of a monosaccharide had been replaced by a methylene moiety, was described in 1966 by Professor G. E. McCasland’s group. Seven years later, the first true natural carbasugar (5a-carba-R-D-galactopyranose) was isolated from a fermentation broth of Streptomyces sp. MA-4145. In the following decades, the chemistry and biology of carbasugars have been extensively studied. Most of these compounds show interesting biological properties, especially enzymatic inhibitory activities, and, in consequence, an important number of analogues have also been prepared in the search for improved biological activities. The aim of this review is to give coverage on the progress made in two important aspects of these compounds: the elucidation of their biosynthesis and the consideration of their biological properties, including the extensively studied carbapyranoses as well as the much less studied carbafuranoses.

Mechanism of Human Nucleocytoplasmic Hexosaminidase D

Mammalian β-hexosaminidases have been shown to play essential roles in cellular physiology and health. These enzymes are responsible for the cleavage of the monosaccharides N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc) from cellular substrates. One of these β-hexosaminidases, hexosaminidase D (HexD), encoded by the HEXDC gene, has received little attention. No mechanistic studies have focused on the role of this unusual nucleocytoplasmically localized β-hexosaminidase, and its cellular function remains unknown. Using a series of kinetic and mechanistic investigations into HexD, we define the precise catalytic mechanism of this enzyme and establish the identities of key enzymic residues. The preparation of synthetic aryl N-acetylgalactosaminide substrates for HexD in combination with measurements of kinetic parameters for wild-type and mutant enzymes, linear free energy analyses of the enzyme-catalyzed hydrolysis of these substrates, evaluation of the reaction by nuclear magnetic resonance, and inhibition studies collectively reveal the detailed mechanism of action employed by HexD. HexD is a retaining glycosidase that operates using a substrate-assisted catalytic mechanism, has a preference for galactosaminide over glucosaminide substrates, and shows a pH optimum in its second-order rate constant at pH 6.5-7.0. The catalytically important residues are Asp148 and Glu149, with Glu149 serving as the general acid/base residue and Asp148 as the polarizing residue. HexD is inhibited by Gal-NAG-thiazoline (Ki = 420 nM). The fundamental insights gained from this study will aid in the development of potent and selective probes for HexD, which will serve as useful tools to improve our understanding of the physiological role played by this unusual enzyme.

Novel Hexosaminidase-Targeting Fluorescence Probe for Visualizing Human Colorectal Cancer

Precise tumor diagnosis and evaluation of disease extent are crucial for treatment of solid cancers. In order to complement the limited ability of the unaided human eye to discriminate tumor tissue and normal tissue, we have developed a series of fluorescence probes activatable specifically in cancer tissues. Here, we describe the design, synthesis, and application of a new fluorescence probe targeting hexosaminidase (HMRef-βGlcNAc), which is located in lysosomes and is overexpressed in several carcinomas, including colorectal cancer. This probe could sensitively detect intracellular hexosaminidase activity in human colorectal cancer cell lines, and could visualize tiny metastatic nodules (smaller than 1 mm) in a mouse model of disseminated human peritoneal colorectal cancer (HCT116). In human colorectal cancer specimens obtained at surgery, the probe showed high tumor sensitivity/specificity, together with a high tumor-to-normal signal ratio. HMRef-βGlcNAc is a promising candidate for clinical application during surgical or endoscopic procedures to treat colorectal cancer.

Molecular cloning and catalytic mechanism of a novel glycosphingolipid-degrading beta-N-acetylgalactosaminidase from Paenibacillus sp. TS12

We report here the molecular cloning, characterization, and catalytic mechanism of a novel glycosphingolipid-degrading β-N-acetylgalactosaminidase (β-NGA) from Paenibacillus sp. TS12 (NgaP). Consisting of 1034 putative amino acid residues, NgaP shares no sequence similarity with known proteins. Recombinant NgaP, expressed in Escherichia coli, cleaved the nonreducing terminal β-GalNAc residues of gangliotriaosylceramide and globotetraosylceramide. The enzyme hydrolyzed para-nitrophenyl-β-N-acetylgalactosaminide ∼100 times faster than para-nitrophenyl-β-N-acetylglucosaminide. GalNAc thiazoline, an analog of the oxazolinium intermediate and potent inhibitor for enzymes adopting substrate-assisted catalysis, competitively inhibited the enzyme. The K(i) of the enzyme for GalNAc thiazoline was 1.3 nM, whereas that for GlcNAc thiazoline was 46.8 μM. Comparison of the secondary structure with those of known enzymes exhibiting substrate-assisted catalysis and point mutation analysis indicated that NgaP adopts substrate-assisted catalysis in which Glu-608 and Asp-607 could function as a proton donor and a stabilizer of the 2-acetamide group of the β-GalNAc at the active site, respectively. These results clearly indicate that NgaP is a β-NGA showing substrate-assisted catalysis. This is the first report describing the molecular cloning of a β-NGA adopting substrate-assisted catalysis.

Mammalian cells contain a second nucleocytoplasmic hexosaminidase

Some thirty years ago, work on mammalian tissues suggested the presence of two cytosolic hexosaminidases in mammalian cells; one of these has been more recently characterized in a recombinant form and has an important role in cellular function due to its ability to cleave beta-N-acetylglucosamine residues from a variety of nuclear and cytoplasmic proteins. However, the molecular nature of the second cytosolic hexosaminidase, named hexosaminidase D, has remained obscure. In the present study, we molecularly characterize for the first time the human and murine recombinant forms of enzymes, encoded by HEXDC genes, which appear to correspond to hexosaminidase D in terms of substrate specificity, pH dependency and temperature stability. Furthermore, a Myc-tagged form of this novel hexosaminidase displays a nucleocytoplasmic localization. Transcripts of the corresponding gene are expressed in a number of murine tissues. On the basis of its sequence, this enzyme represents, along with the lysosomal hexosaminidase subunits encoded by the HEXA and HEXB genes, the third class 20 glycosidase to be identified from mammalian sources.

Beta-N-acetylhexosaminidase: a target for the design of antifungal agents

This review provides biochemical, analytical, and biological background information relating to beta-N-acetylhexosaminidase (HexNAc'ase; EC 3.2.1.52) as an emerging target for the design of low-molecular-weight antifungals. The article includes the following: (1) a biochemical description of HexNAc'ase (reaction catalyzed, nomenclature, and mechanism of action) that sets it apart from other, similar enzymes; (2) an overview and a critical evaluation of methods to assay the enzyme, including in crude extracts (photo- and fluorometric procedures with model substrates; HPLC/pulsed amperometric detection of N-acetylglucosamine and chito-oligomers; end-point vs. rate measurements); (3) a summary of some general characteristics of HexNAc'ases from fungi and organisms of other types (Km values, substrate preference, and glycoconjugation); (4) an hypothesis of a specific target function of wall-associated HexNAc'ase (a component of the assembly of surface-located enzymes effecting a continuous turnover and remodelling of the wall fabric through its combined hydrolytic and transglycosylating activities, and a mediator enzyme acting in concert with chitinase and chitin synthase to provide for the controlled lysis and synthesis of chitin during growth); (5) a tabulation of the structural formulae of reaction-based HexNAc'ase inhibitors with Ki values < or = 100 microM (some of them representing transition state mimics that could serve as leads for the development of new antifungals); and (6) an outline of approaches towards the establishment of a three-dimensional model of HexNAc'ase suitable for a truly rational design of antimycotics as well as agricultural fungicides.

Rate assay of N-acetyl-beta-D-hexosaminidase with 4-nitrophenyl N-acetyl-beta-D-glucosaminide as an artificial substrate

A rapid and accurate rate assay method for N-acetyl-beta-D-hexosaminidase (EC 3.2.1.52, also known as N-acetyl-beta-D-glucosaminidase, or NAGase) using 4-nitrophenyl N-acetyl-beta-D-glucosaminide (NP-GlcNAc) as an artificial substrate was developed using diethylaminoethyl-alpha-cyclodextrin (DEn-CD, where n is the number of diethylaminoethyl groups introduced to alpha-cyclodextrin), as an additive to ionize 4-nitrophenol to yellow-colored 4-nitrophenoxide at pH near 5, where the enzyme acts optimally. A possible recipe for the rate assay of NAGase is as follows. Prepare a stock solution containing 4.8 mmol/l NP-GlcNAc and 1% DEn-CD (n is preferably near 17) in 0.1 mol/l glycolate buffer, pH 5.50. Introduce the stock solution and a properly diluted sample (urine or other body fluid) to a reaction cell placed in a spectrophotometer at a ratio of 1:1, and monitor the absorbance at 400 or 420 nm. The reaction rate (enzymatic activity) can be conveniently read directly from calibration plots prepared for a given lot of DEn-CD sample, or can be calculated from the rate of the absorbance increase, ionization degree of 4-nitrophenol at pH 5.50, and the millimolar absorbance coefficient of 4-nitrophenoxide in the presence of 0.5% DEn-CD.

Postnatal development of glycosidases and gangliosides in the rat central nervous system

The developmental profiles of sialidase, beta-galactosidase, beta-hexosaminidase and beta-glucosidase were compared to those of the gangliosides in rat brain and spinal cord. The glycosidase activities (enzyme units/g wet tissue), except beta-galactosidases, were found to be higher in brain than spinal cord, in adult rats. Among the hydrolases, beta-hexosaminidase showed a higher level of activity in both brain and spinal cord. In brain, the hydrolases, except beta-glucosidase, followed a similar developmental pattern, showing an increase from birth to 21 days, and then decreased to adult values by day 90. In the spinal cord, sialidase, beta-galactosidase, pH 3.1, and beta-hexosaminidase activities increased from birth to 21 days, reaching peak values. These activities then declined to adult values by 90 days of age. However, beta-galactosidase, pH 4.5, and beta-glucosidase activities showed a peak at day 14. Brain total ganglioside concentration (microgram N-acetylneuraminic acid/g tissue) increased slowly between birth and 7 days of age, followed by a rapid phase of increase to attain a peak value by day 21. The concentration of total gangliosides in the spinal cord is less when compared to the brain. The proportions of individual gangliosides in the central nervous system also vaired during development. The rapid phase of increase in enzyme activities between 0-7 and 14-21 days and a decrease thereafter is consistent with the turnover rate of gangliosides, which in rat brain is reported to be highest between 10 and 20 days.

Neonatal undernutrition and short term administration of hydrocortisone and thyroxine: effects on rat brain hydrolases

Brain enzymes activities that are likely to be involved in the catabolism of gangliosides were determined in controls (20% casein diet), postnatally undernourished (6.5% casein diet) and undernourished rats treated with either thyroxine or hydrocortisone, at 21 days of age. Postnatal undernutrition imposed by maternal protein deficiency during lactation resulted in a decrease in body weight and brain wet weight of the pups at 21 days of age. Administration of thyroxine or hydrocortisone to the undernourished pups every day between 16 and 21 days caused a further decrease in the body weight of the pups. On the other hand, the wet weight of brain showed a slight gain following hydrocortisone treatment. Postnatal undernutrition during lactation elevated the activities of beta-glucosidase, beta-galactosidase, beta-hexosaminidase and sialidase in rat brain. Short-term administration of thyroxine or hydrocortisone to the undernourished pups, every day between 16 and 21 days postnatal age decreased the enzyme activities. However, reversal of the increased enzyme activities to the normal lower level was completed only in the case of undernourished pups treated with hydrocortisone.

Alterations and recovery of rat brain gangliosides and glycosidases following long-term exposure to alcohol and rehabilitation during development

The present study examines effects of continuous exposure to alcohol during gestation, lactation and postweaning periods and rehabilitation on gangliosides and their catabolizing enzymes in whole brain (WB), cerebrum (C), cerebellum (CB) and brain stem (BS) of 63-day-old rats. Continuous exposure to alcohol was found to cause significant deficits in the body and brain weights. On the other hand, the concentration of total ganglioside in whole brain, cerebrum, cerebellum and brain stem showed an increase following exposure to alcohol. In agreement with the increased ganglioside concentration the activities of sialidase, beta-galactosidase, beta-glucosidase and beta-hexosaminidase, which are likely to be involved in the catabolism of gangliosides, showed reductions due to alcohol. Alcohol was also found to alter the proportions of individual gangliosides and the changes were found to be region-specific. However; the alcohol-induced alterations were reversed, at least to some extent, upon abstinence from alcohol. Body weights of control (CT), alcoholic (AC) and rehabilitated (AR) rats were 164 +/- 2, 107 +/- 7 and 139 +/- 3 (mean +/- S.E.M.), respectively. Decrease in tissue weight was significant in whole brain, cerebrum and brain stem but not in cerebellum. In AR rats significant deficits in tissue weights persisted in cerebrum and almost a complete recovery was observed in brain stem. On the other hand, the increase in the concentration of gangliosides in WB, C, CB and BS of AC rats amounted to 23, 19, 19 and 53% of controls, respectively. The corresponding values for the AR rats were 12, 14, 3 and 5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of prenatal and postnatal exposure to ethanol on rat central nervous system gangliosides and glycosidases

We investigated the effect of maternal alcohol consumption on cell number, gangliosides and ganglioside catabolizing enzymes in the central nervous system (CNS) of the offspring. Virgin female rats of the Charles Foster strain were given 15% (v/v) ethanol in drinking water one month prior to conception and during gestation and lactation. At 21 days postnatal age, the offspring were sacrificed and the brains were separated into cerebrum, cerebellum and brain stem to investigate possible regional variations. Compared to controls, wet weight of cerebrum, cerebellum and brain stem, and of spinal cord was decreased in the pups exposed to alcohol. DNA and protein contents were also found to be lowered in all the CNS regions of the pups exposed to alcohol. Conversely, maternal alcohol consumption was found to increase the concentration and the content of total ganglioside N-acetyl-neuraminic (NANA) in CNS of the pups. In addition, alcohol treatment was found to induce alterations in the proportions of individual ganglioside fractions. Interestingly, these alterations are somewhat different than those observed in the neonatal brain and spinal cord of the pups subjected to prenatal alcohol exposure. The alterations in the proportions of ganglioside fractions were shown to be region-specific. Maternal alcohol consumption resulted in decreased activities of sialidase, beta-galactosidase, beta-glucosidase and beta-hexosaminidase. The results suggest that the alcohol-associated increases in ganglioside concentration may be at least partly due to the decreased activities of ganglioside catabolizing enzymes.

Maternal alcohol consumption and undernutrition in the rat: effects on gangliosides and their catabolizing enzymes in the CNS of the newborn

Consumption of fifteen percent alcohol, during gestation did not cause any decrease in the total calorie or fluid intake of the rats maintained on normal dietary regimen. However, the alcohol consumption by gestating mothers resulted in a decreased contents of both DNA and protein in the CNS of the in utero alcohol exposed pups at birth. DNA content was also found to be less in the undernourished pups compared to the normal pups. On the other hand an increase in the total gangliosides and a decrease in the ganglioside catabolizing enzymes was observed in the brain and spinal cord of alcoholic pups at birth. However undernutrition resulted in a decrease in the content of total gangliosides both in brain and spinal cord. Maternal alcohol consumption and undernutrition had also resulted in an altered proportions of the individual ganglioside fractions.

Irreversible inhibition of hexosaminidase C by medium-chain monocarboxylic acids and Triton X-100

The neutral beta-N-acetylhexosaminidase (hexosaminidase C) from human brain was partially purified (separated from lysosomal beta-N-acetylhexosaminidases by chromatography on a Con A-Sepharose column). Hexosaminidase C was inhibited by medium-chain fatty acids (monocarboxylic acids with chain-length between C6 and C9), whereas shorter-chain monocarboxylic acids showed no inhibitory effect. Studies on the inhibition mechanism showed an irreversible and pH-dependent inhibition which progresses with time and which is not reversed by the removal of fatty acids (by Bio-Beads SM-2). Similar inhibitory effects were also obtained using Triton X-100 (but not with homologous alkylamines). These results suggest that the hexosaminidase C inactivation is related to the hydrophobic properties of the inhibitor which acts as a denaturing agent mainly at acidic pH. The possibility has been discussed that this inactivation effect of monocarboxylic acid on hexosaminidase C could constitute a molecular model of the toxicity of medium-chain-length fatty acids.

Fast protein liquid chromatography (FPLC) of leukaemic cell N-acetyl beta-D hexosaminidases

Leukaemic myeloid and lymphoid cell N-acetyl beta-D glucosaminidase (hexosaminidase) enzymes were fractionated by Fast Protein Liquid Chromatography (FPLC) using high-resolution ion exchange (Mono-S and Mono-Q), gel filtration (Superose-6) and chromatofocusing (Mono-P) columns. Although only one molecular weight species was detected in haemopoietic cells, with an apparent mass of 129 kD, "isoenzyme" variants defined by differences in molecular charge were considerably more diverse than previously thought. Separation of the major Hex forms (A and B) by chromatofocusing indicated that intermediate (I) components were present in most acute leukaemias irrespective of lineage supporting the concept that the I form is a non-specific marker of haemopoietic immaturity. Substrate and inhibitor studies further revealed that leukaemic cell hexosaminidases hydrolyse galactopyranosides at significantly lower rates than glucopyranosides and that the hydrolysis of N-acetyl beta-D glucosamine is inhibited by both glucosamine and galactosamine products.

Purification and properties of beta-N-acetyl-D-hexosaminidase from boar seminal plasma

beta-N-Acetyl-D-hexosaminidase has been purified ca. 190-fold to homogeneity from boar seminal plasma. It catalyzed the hydrolysis of the p-nitrophenyl-N-acetyl derivatives of both beta-D-glucosaminide and beta-D-galactosaminide but was inactive with the o- or p-nitrophenyl glycosides of other monosaccharides. Its pH optimum was 4.5 and its KM was 1.5 mM with p-nitrophenyl-N-acetyl-beta-D-glucosamide as substrate. The enzyme was inhibited by mercuribenzoate compounds but not by iodoacetamide, 2,2'-dipyridyl disulfide, methylmethane thiosulfonate, nor N-ethylmaleimide. The active enzyme had mol. wt ca. 250,000 by Sephacryl S-300 chromatography. SDS electrophoresis showed single bands corresponding to subunit mol. wts ca. 62,000 and 107,000 depending on whether the enzyme had been denatured in the presence of 2-mercaptoethanol or not. These data suggest that the enzyme is a tetramer of identical subunits, pairs of which are held together by disulfide bonds.

Canine GM2-gangliosidosis: chemical and enzymatic features

The chemical and enzymatic features in tissues of GM2-gangliosidosis are characterized by the analysis of glycolipids and FD-MS, and also by enzymatic analysis with DEAE-Sepharose column chromatography. The results suggest that canine GM2-gangliosidosis is equivalent to human juvenile GM2-gangliosidosis.

Degradation of biogenic oligosaccharides by beta-N-acetyl-glucosaminidase secreted by Entamoeba histolytica

beta-N-Acetylglucosaminidase secreted by Entamoeba histolytica was extracted from the growth medium by affinity chromatography on CH-Sepharose 4 B coupled to p-aminophenyl-1-thio-beta-2-acetamido-2-deoxyglucopyranoside. The enzyme was further purified by isoelectric focusing, by sequential chromatography on DEAE-cellulose and Sephadex G-150, and by preparative disc gel electrophoresis. Chitobiose (betaGlcNAc1-4GlcNAc) derived from chitin as well as the oligosaccharides betaGlcNAc1-4 betaGlcUA1-3GlcNAc, betaGlcNAc1-4 betaGlcUA1-3 betaGlcAc1-4GlcUA, and betaGlcNAc1-4 betaGlc-UA1-3 betaGlcNAc1-4 betaGlcUA1-3 betaGlcNAc1-4GlcUA derived from hyaluronic acid were tested as potential physiological substrates. All these oligosaccharides are susceptible to action of beta-N-acetylglucosaminidase from E. histolytica. Under identical conditions chitobiose is cleaved 38-48 times faster than hyhyauronate oligosaccharides. No release of N-acetylglucosamine was observed when glycopeptides from ovalbumin were used as substrate. The pH optimum of hydrolase activity was 4.5 when chitobiose was used as substrate. Optimal hydrolysis of aluronate oligosaccharides was observed at pH 3.0 for trisaccharide and pH 2.0 for tetra- and hexasaccharide, respectively. Estimation of molecular weight by means of gel filtration gave values of 75 000. The isoelectric point was 5.02 beta-N-Acetylglucosaminidase from E. histolytica does not act on macromolecular chitin and hyaluronic acid.

Development-dependent regulation of N-acetyl-beta-D-hexosaminidase of cerebellum and cerebrum of normal and staggerer mutant mice

Distinctive activities of various glycosidases were expressed in the cerebellum and cerebral cortex of mice during their development. In particular, N-acetyl-beta-D-hexosaminidase (EC 3.2.1.30) appeared to be developmentally regulated. A transient peak of enzyme activity at postnatal day 7 was characteristic for the cerebellum, whereas the activity in the cerebral cortex gradually increased through the 1st postnatal month and was maintained at a high level of activity throughout adulthood. The regulation of N-acetylhexosaminidase activity in the developing cerebellum of the staggerer mouse deviated clearly from enzyme activities in the wild-type, whereas the activity pattern in the staggerer cerebral cortex remained unaffected. In experiments mixing wild-type and staggerer cerebellum homogenates, the specific activity was additive. Thus, involvement of inhibitors or activating molecules can be excluded. This developmentally controlled regulation or disregulation in staggerer appears to be enzyme specific, sine beta-glucosidase, alpha-glucosidase, and beta-galactosidase did not exhibit such a pattern in either normal or staggerer mice. In the mutation weaver that, like staggerer, loses the majority of its cerebellar granule cells, N-acetyl-beta-hexosaminidase activity of the cerebellum was not elevated, indicating a specific defect in staggerer rather than a general effect on lysosomal enzymes due to cell death.

Isolation and further characterization of bovine brain hexosaminidase C

Hexosaminidase C (2-acetamido-2-deoxy-beta-D-glucoside acetamidodeoxyglucohydrolase, EC 3.2.1.30) was partially purified from bovine brain tissue. The resulting preparation, free of its lysosomal counterparts, was used for the characterization of the enzyme and for further purification (lectin affinity chromatography, hydrophobic interaction chromatography, substrate-ligand affinity chromatography, ion-exchange chromatography, chromatography on activated thiol-Sepharose 4B). Only ion-exchange chromatography on DEAE-Sephacel appeared to improve the purity. The Michaelis constant was 0.46 mM for the substrate 4-methyl-umbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside. The enzyme was not inhibited by acetate or N-acetylgalactosamine. Inhibition by N-acetylglucosamine was competitive, with a Ki value of 8.0 mM. Inhibition by divalent metal ions increased in the order Fe less than Zn less than Cu. Dithiothreitol and beta-mercaptoethanol, at an optimum concentration of about 10 mM, stimulated the activity. The enzyme is apparently not a glycoprotein since it did not bind to various lectins, nor did sialidase change its isoelectric point.

The effect of membrane phospholipid acyl-chain composition on the activity of brain-beta-N-acetyl-D-glucosaminidase

The phospholipid acyl-chain dependence of the membrane-bound lysosomal beta-N-acetyl-D-glucosaminidase has been examined on control membranes from rat brain primary cell cultures and on membrane modified by culturing the cells in media supplemented with polyunsaturated fatty acids. The relationship between beta-N-acetyl-D-glucosaminidase activity and the membrane phospholipid acyl-chain composition has been evaluated. An increase in the unsaturation level of phosphatidyl ethanolamines and phosphatidylcholines, the most abundant phospholipids in this membrane fraction, is related to the rate of the enzymic reaction. The Arrhenius plot of the enzyme activity in modified membranes shows break-temperatures, starting from approximately 15 degrees C. The apparent activation energy below and above the break-temperature is not correlated with phospholipid acyl-chain unsaturation.

Multiple sulfatase deficiency (mucosulfatidosis): impaired degradation of labeled sulfated compounds in cultured skin fibroblasts in vivo

Skin fibroblasts from a Japanese patient with multiple sulfatase deficiency (MSD) (Mucosulfatidosis) were studied with regard to metabolism of various sulfated compounds in vivo. Several sulfatase activities (arylsulfatases A, B and C, cholesterol sulfatase, heparin N-sulfatase) were deficient in skin fibroblasts grown in F-10 CO2 medium. The accumulation and degradation of 35S-sulfatide, 35S-mucopolysaccharides, 14C-cholesterol sulfate by MSD cells were also studied, comparing them to control, Hunter and metachromatic leukodystrophy cells. MSD fibroblasts accumulated and failed to degrade these compounds in vivo. Cholesterol sulfate was also incorporated into the control and pathological cells, and MSD cells were unable to hydrolyze cholesterol sulfate, though cholesterol sulfate is known to be hydrolyzed in the non-lysosomal subfraction. From these data it is clear that multiple enzyme deficiencies in MSD fibroblasts can be demonstrated in vivo.

Neutral hydrolases of rat brain. Preliminary characterization and developmental changes of neutral beta-N-acetylhexosamindases

The bulk of rat brain neutral beta-N-acetylhexosaminidases (2-acetamido-2-deoxy-beta-D-hexoside acetamidodeoxyhexohydrolase, EC 3.2.1.52) were present in the cytosol fraction. They were not bound by concanavalin A-Sepharose while the acid beta-N-acetylhexosaminidases were all bound. The neutral beta-N-acetylgalactosaminidase had a pH optimum of 5.2 and Km of 0.57 mM, while the neutral beta-N-acetylgalactosaminidase had the highest reaction rate at lost more than 90% of the activity in 30 min at 50 degrees C. The galactosaminidase pH 6.0 with a Km of 0.12 mM. No divalent ions activated either of the enzymes. The galactosaminidase was heat-stable and lost only 10--20% of its activity after 3 h at 50 degrees C. The neutral glucosaminidase was inhibited by free N-acetylglucosamine but not by N-acetylgalactosamine. The reverse was found for the neutral beta-galactosaminidase. Two enzymes were separated almost completely by hydroxyapatite chromatography. Heat stability of the separated activity peaks suggested that the neutral beta-N-acetylgalactosaminidase, which was not bound to hydroxyapatite, may be specific to the galactosaminide substrate. The neutral beta-N-acetylglucosaminidase may, on the other hand, have some activity toward the galactosaminide substrate. Both of the neutral enzyme activities were highest during the first postnatal week in rat brain in contrast to the acidic enzyme which showed peak activities during the second and third weeks. These results confirmed and expanded earlier observations by Frohwein and Gatt in calf brain. The relationship of these enzymes to the hexosaminidase C in human tissues is less certain at the present time.

A quantitative study of N-acetyl-beta-glucosaminidase activity in unfixed tissue sections of the guinea-pig thyroid gland

A post-coupling procedure for the quantitative measurement of N-acetyl-beta-glucosaminidase activity in unfixed tissue sections of guinea-pig thyroid is described. The method depends on the cleaving of a naphthol AS-BI substrate and the insoluble reaction product is post-coupled with Fast Garnet GBC salt (in acetate buffer, pH 6.2) at 4 degrees C. Even though this enzyme is localized in the lysosomes, an inert colloid stabiliser, polyvinyl alcohol (G18/140) is included in the reaction medium to allow the use of the optimal substrate concentration (0.5 mg/ml) whilst employing a low concentration (5%) of ethylene glycol monomethyl ether. The high molecular weight (90 000) grade of polyvinyl alcohol used did not stabilize the lysosomal membrane, although a lower molecular weight (15 000) grade of polyvinyl alcohol (G04/140) may do. The enzyme activity was not affected by the metal ions Ca2+ and Zn2+ and was totally abolished by the specific inhibitor 2-acetamido-2-deoxy-D-gluconolactone.

The multiple forms and kinetic differences of rat colonic beta-N-acetylhexosaminidases

Rat colonic beta-N-acetylhexosaminidase (2-acetamido-2-deoxy-beta-D-glucoside acetamidodeoxyglucohydrolase, EC 3.2.1.30) has been separated into three forms by DEAE-cellulose chromatography with an increasing salt gradient. It was not possible to separate the glucosaminidase activity from the galactosaminidase activity by a variety of chromatographic procedues, but the ratio of the two specific activities varied during purification. The pH optima were however identical, for both activities and all three forms. Kinetic measurements including inhibition by substrate analogues showed differences between the two activities as well as among the three forms. A common active site model was inconsistent with the results. Data from mixed substrate experiments were consistent with a model wherein the two activities reside in seperate active sites, each able to be inhibited by the substrate for the other site. The effect of acetate and SH reagents confirmed the two-site model. Treatment with neuraminidase, thimerosal, p-hydroxymercuribenzoate, HgCl2 and AgNO3 or heating at 50 degrees C did not produce any effect on the A form that could be identified as a conversion to the B form. Measurement of the effects on both activities supported the two-site model. It is concluded that the relationship between the A and B forms in the rat colonic mucosa hexosaminidases must be different from that reported for such enzymes from other sources.

Bile lysosomal enzymes: characteristics and pathological significance for various hepatobiliary disorders

The activities of several glycosidases (beta-galactosidase, beta-glucosidase, N-acetyl-beta-glucosaminidase) were demonstrated in human bile. The enzyme activities are increased about 100 times after exclusion of bile salts and other small molecular compounds by Sephadex G-50 gel filtration. The use of 4-methylumbelliferyl derivatives as substrates was useful as measurement of the bile enzyme activities are not altered in the presence of bile pigments. Enzyme characteristics of bile glycosidases were determined: pH optimum and isoelectric point. The bile glycosidase activities were also measured in various hepatobiliary disorders (cholelithiasis, cancer of gallbladder, acute hepatitis, liver cirrhosis and fatty liver). The glycosidase activities in bile from patients with liver diseases, as well as with cholelithiasis, were generally decreased. Isoelectric focusing patterns of biliary glycosidases were similar for specimens from patients with hepatobiliary disorders as compared to normal.

The separation of bovine brain beta-N-acetyl-D-hexosaminidases. Abnormal gel-filtration behaviour of beta-N-acetyl-D-glucosaminidase C

Bovine brain tissue was extracted and the 50 000g supernatant was separated by electrophoresis, DEAE-Sephadex chromatography and gel filtration on Sephadex G-200 and Bio-Gel P-200. The electrophoretic separation showed that the beta-N-acetyl-D-hexosaminidases (hexosaminidases) of bovine brain tissue were composed of four different fractions. Two fractions (A and B) exerted both glucosaminidase and galactosaminidase activity, a third fraction (C) showed only glucosaminidase activity, whereas a fourth form (D) with specificity towards the galactosaminide moiety was found to be present. DEAE-Sephadex chromatography at pH 7.0 showed that the B form was eluted with the void volume, whereas the A and D forms could be eluted in one peak by raising that salt concentration. The C form could not be detected in the eluate. Gel filtration on Sephadex G-200 showed that the B, A and D forms had almost equal molecular weights. In this case also the C form could not be detected in the column eluates. Gel filtration on Bio-Gel P-200 revealed that the C form was eluted with the void volume.

Hexosaminidase C in Tay-Sachs and Sandhoff disease

1. Hexosaminidase C has been purified from human placenta. Complete separation from hexosaminidases A and B was achieved. 2. The following properties of hexosaminidase C differ from those of the A and B isozymes. Presence in the supernatant rather than the lysosomes, neutral pH optimum, higher molecular weight, lack of activity on beta-N-acetylgalactosamine derivatives, and lack of immunological relationship. 3. Hexosaminidase C is active in patients deficient in hexosaminidases A and B and can be recognized by its characteristic electrophoretic mobility. It is concluded that the genetic origin of hexosaminidase C is probably different from that of hexosaminidases A and B.

N-acetyl-beta-hexosaminidase: role in the degradation of glycosaminoglycans

Extracts of cultured normal human skin fibroblasts released radioactivity from a (14)C-labeled heptasaccharide prepared by addition of [(14)C]N-acetylgalactosamine to the nonreducing terminus of a hexasaccharide derived from chondroitin 4-sulfate whereas fibroblast extracts from patients with Tay-Sachs and Sandhoff-Jatzkewitz diseases did not. The results suggest that N-acetyl-beta-hexosaminidase A is responsible for degradation of the oligosaccharide substrate.