Purification and properties of brain N-acetyl-beta-hexosaminidase A

Properties of the isoenzyme forms A-1, A-2 and B of N-acetyl-beta-D-glucosaminidase purified from baboon kidneys

Three forms of N-acetyl-beta-D-glucosaminidase (NAG: A, B and I) were separated from baboon kidney using Con A-Sepharose and DEAE-Trisacryl chromatography. 2. The A form was further purified into two forms A-1 and A-2 using hydroxylapatite chromatography and anodic PAGE. Both were homogeneous on SDS-PAGE and anodic PAGE but microheterogeneous on PAG-IEF, which could be eliminated by prior treatment with endoglycosidase H or glycopeptidase F. 3. The carbohydrate content accounted for some of this microheterogeneity since it varied from 31 for A-1 to 17% for A-2 and the sialic acid was 6 and 1%. Deamidation may also contribute since the acidic amino acids (29 mol%) and ammonia were high following acid hydrolysis. 4. The mol. wt for A-1, determined by SDS-PAGE, was 52.1 K. 5. The pH optimum was 4.55 and the pI4.97. 6. The optimum temperature for NAG A and B was 50 degrees and 42 degrees C, but B retained more activity above 55 degrees C. 7. The Km for N-acetyl-beta-D-glucosamine and -galactosamine for both isoforms was 0.497 and 0.627 mM respectively. 8. Several ions were found to be uncompetitive inhibitors. Ag+ and Pb2+ were the most potent having Ki values of 3.6 and 8.5 mM respectively. Acetate acted as a competitive inhibitor.

Purification, biochemical properties and active sites of N-acetyl-beta-D-hexosaminidases from human seminal plasma

Two isoenzymes of N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30) (Hex A and Hex B) from human seminal plasma were purified to homogeneity with specific activities of 26 and 60 units/mg of protein respectively. N-Acetyl-beta-D-glucosaminidase activity was inseparable from N-acetyl-beta-D-galactosaminidase activity in both Hex A and Hex B by various conventional chromatographic procedures. Although Km values of N-acetyl-beta-glucosaminidase activity of Hex A and Hex B were similar (1.33 mM), those of N-acetyl-beta-galactosaminidase activity were 0.14 mM for Hex A and 0.40 mM for Hex B. However, pH optima and temperature optima were identical for N-acetyl-beta-glucosaminidase and N-acetyl-beta-galactosaminidase activities of both isoenzymes; Hex A was far more heat-sensitive than Hex B. Thiol-reactive compounds such as silver salts, mercuric salts, p-chloromercuribenzoate and thimerosal strongly inhibited the N-acetyl-beta-glucosaminidase activities of both isoenzymes. GSH protected the enzyme activities from inactivation caused by these reagents, confirming the presence of thiol groups at the active centres. Inhibitions of N-acetyl-beta-glucosaminidase activities of both isoenzymes by metal salts and organic anions were comparable; acetate and arsenite were effective inhibitors for both isoenzymes. In contrast, inhibitions of N-acetyl-beta-glucosaminidase activities of the two isoenzymes by iodoacetic acid, iodoacetamide and ethylmaleimide were not comparable; Hex B was more susceptible to inhibition by these agents at 20 mM concentration. The N-acetyl-beta-glucosaminidase activities of both isoenzymes are strongly inhibited, in decreasing order, by N-acetyl-galactosamine, mannosamine, disaccharic acid lactone, N-acetylglucosamine and gluconolactone. The Ki values of the N-acetyl-beta-glucosaminidase and N-acetyl-beta-galactosaminidase activities for N-acetylhexosamines and results from mixed-substrate kinetics indicated that the activities for the two substrates are located at different sites in Hex A and at the same site in Hex B. The Mr values of Hex A and Hex B were determined to be 195,000 and 210,000 respectively by gel filtration through Sephadex G-200. SDS/polyacrylamide-gel electrophoresis revealed that Hex A and Hex B are each composed of four subunits corresponding to Mr about 50,000 each. No further polypeptide chain was obtained after reduction and alkylation of Hex A and Hex B with 10 mM-dithiothreitol and 10 mM-iodoacetamide.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

Two forms of acid alpha-D-mannosidase in monkey brain: evidence for the co-existence of high mannose and complex oligosaccharides in one form

Lysosomal alpha-D-mannosidase of monkey brain existed in two forms. One form of mannosidase was bound to the Ricinus communis agglutinin120 (RCA1)-Sepharose and could be specifically eluted with lactose. The other form did not bind to the RCA1-Sepharose. Both forms of mannosidase could bind to a similar extent to the immobilized brain lysosomal receptor protein. Both the forms were purified to apparent homogeneity. Neutral sugar analysis by GLC showed the presence of glucose, mannose and galactose in the RCA1-Sepharose bindable mannosidase and glucose and mannose in the non-bindable mannosidase. Several other brain lysosomal hydrolases did not bind to the RCA1-Sepharose. The results suggested the existence of only high mannose oligosaccharides in the RCA1 non-bindable mannosidase and both high mannose and complex oligosaccharides in the bindable mannosidase.

Molecular forms of beta-N-acetylhexosaminidase in Epstein-Barr virus-transformed lymphoid cell lines from normal subjects and patients with Tay-Sachs disease

In whole leukocytes and in lymphocytes from normal subjects, the percentage activity of heat-stable beta-N-acetylhexosaminidase (30 +/- 5% and 45 +/- 5%, respectively) was higher than in the transformed lymphoid cell line (19 +/- 3%). In Tay-Sachs transformed cells as well as non-transformed beta-N-acetylhexosaminidase was almost completely heat-stable (95 - 98%). In the transformed cells from normal subjects, the beta-N-acetylhexosaminidase B (Hex B) activity (5% of total) was significantly lower than in blood lymphocytes (average 25 - 30% of total activity), whereas Hex A and Hex I were similar in the either cell type. Blood lymphocytes and lymphoid cell lines established from a Tay-Sachs patient lacked heat-labile Hex A and expressed high heat-stable Hex I and Hex B activities (3-6-fold). After neuraminidase treatment, Hex A peak sharpened while Hex I peaks switched to higher pI than normal Hex I, in the region of Hex B. PreHex A/S pI was not affected. Hydrolytic properties using the both substrates (4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside and 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-galactopyranoside) of each molecular form were similar in transformed and non-transformed cells. Data derived from the use of a mixture of substrates were consistent with the model which proposes a common active site for either substrate in the case of preHex A, Hex B and Hex I, but not for Hex A. Thus Epstein-Barr virus-transformed lymphoid cell lines represent an accurate model system for studies on Tay-Sachs disease.

Lysosomal and microsomal beta-glucuronidase of monkey brain. Differential elution characteristics from con A-sepharose and neutral sugar composition

Microsomal and lysosomal beta-glucuronidase (beta-D-glucuronide glucuronosohydrolase, EC 3.2.1.31) of monkey brain were differentially eluted from Con A-Sepharose when subjected to chromatography and linear gradient elution with methyl alpha-glucoside at 28+/-1 degree C. The lysosomal enzyme was eluted as a sharp peak in the first few fractions, while the microsomal enzyme was eluted as a broad peak extending over several fractions. This differential pattern of elution was dependent only on the temperature of elution and the concentration of methyl alpha-glucoside used. The lysosomal and microsomal glucuronidases were purified to apparent homogeneity and their neutral sugar analysed. Both of them contained glucose, mannose and fucose but the microsomal enzyme contained about 3-times as much of all these sugars as the lysosomal enzyme. Sodium periodate treatment of the microsomal enzyme resulted in a shift in its elution pattern, similar to the lysosomal enzyme when subjected to Con A-Sepharose chromatography. The content of neutral sugars and the structural features of the oligosaccharide units in the microsomal glucuronidase might be responsible for its elution pattern. A processing of the carbohydrate units of the microsomal glucuronidase might be envisaged to take place if it were to act as a precursor of the lysosomal glucuronidase.

Purification and partial characterization of the carbohydrate structure of lysosomal N-acetyl-beta-D-hexosaminidases from bovine brain

1. The lysosomal forms A and B, and an intermediate form I of N-acetyl-beta-D-hexosaminidase (EC 3.2.1.30) were isolated from bovine brain, resulting in the following purification factors and specific activities: hexosaminidase A 20255, 103 U mg-1; hexosaminidase B 34715, 134 U mg-1; hexosaminidase I 15241, 78 U mg-1. 2. The molecular weights of the polypeptide chains were identical for each isoenzyme: two bands of 50 and 53 k daltons were found. 3. Carbohydrate analysis showed the presence of mannose, galactose, N-acetylglucosamine and sialic acid. This composition, and the absence of N-acetylgalactosamine, indicated that only N-glycosidically linked oligosaccharide chains are present. 4. The amino-acid composition showed no substantial differences for the three isoenzymes.

Chromatographic components of beta-hexosaminidase in I-cell disease (mucolipidosis II)

Isozymes of N-acetyl-beta-D-hexosaminidase in body fluids, culture medium, postmortem organs, and cultured fibroblasts from patients with I-cell disease were resolved by ion exchange column chromatography. The elution pattern was compared in detail with that of the isozymes in control samples. This approach revealed no qualitative differences between the isozymes from the two sources. There is a relative increase of the neuraminidase-sensitive components of hexosaminidase in I-cell disease. This phenomenon is probably related less to the unknown primary defect of the disorder than to the quantitative change in the distribution of hexosaminidase components between the intra- and the extracellular compartment.

Purification and some properties of liver and brain beta-N-acetyl-hexosaminidase S

beta-N-Acetyl-hexosaminidase S (2-acetamido-2-deoxy-beta-hexoside acetamido-deoxyhexohydrolase, EC 3.2.1.52) was purified from liver and brain of a patient deceased of type O GM2 gangliosidosis (Sandhoff's disease). Brain beta-N-acetyl-hexosaminidase S was further purified by preparative polyacrylamide gel electrophoresis. The pH optimum of the purified liver and brain enzyme was 5.0 and Km values were 0.8--0.9 mM and 0.3--0.4 mM with 4-methylumbelliferyl-beta-D-N-acetylglucosamine and beta-D-N-acetylgalactosaminide derivatives, respectively. beta-N-Acetyl-hexosaminidase S was thermolabile losing most of its activity after 50 min at 50 degrees C. The apparent molecular weights of the purified liver and brain enzymes were 154 000 and 152 000, respectively. Hexosamines activated beta-N-acetyl-hexosaminidase S whereas the isoenzyme A and B were inhibited. The glycoprotein nature of beta-N-acetyl-hexosaminidase S was suggested by its affinity towards Concanavalin A-Sepharose.

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.