Neuraminidase activity in brain and liver of rats during development

Neuraminidase activity in different regions of the seizing epileptic and non-epileptic brain

The sialic acid in the brain is split from sialoglucoconjugates by sialidases (neuraminidases, EC 3.2.1.18), and is postulated to act as an inhibitor of cellular adhesion and to play a role in various membrane functions. Since epilepsy alters cellular interactions and connectivity, it is reasonable to propose that sialidases can be affected by this pathological state or, alternately, by seizures. Therefore, we studied the activity of total, soluble, and membranal sialidases in various brain regions in normal, kindled epileptic and non-epileptic seizing rats. The results showed that in kindled rats, the total activity of the sialidases significantly decreased in cerebral cortex (11.38%) and cerebellum (28.58%), whereas it increased in brainstem (35.51%), hypothalamus (2.88%) and hippocampus (9.37%). The activity of the membranous sialidases in kindled rats followed the same pattern as the total activity, whereas the activity of soluble sialidase was significantly lower than membranous activity. Interestingly, the activity of total and membranal sialidases in non-epileptic seizing rats paralleled that observed in kindled rats. We suggest that the seizure-induced decrease of sialidasic activity may not modify the number of sialic acid molecules bound to gangliosides in cell membranes, as compared to areas of increased activity, that may decrease them. These changes in sialidases' activity may reflect functional disturbances of membrane polysialylated gangliosides related to the functional and anatomical plastic changes associated to seizures. Our data indicate that these changes are related to the presence of seizures rather than to an established epileptic state.

Age-dependent reduction in sialidase activity of nuclear membranes from mouse brain

Sialidase is an enzyme that cleaves alpha-linked sialic acid residues from sialoglycoconjugates and participates in various cellular functions. In the present study, we characterized sialidase activity in nuclear membranes from mouse brain and examined its age-related changes. A highly purified nuclear membrane preparation from 4-week-old mouse brain contained sialidase activity that hydrolyzed both 4-methylumbelliferyl-alpha-D-N-acetylneuraminic acid (4MU-Neu5Ac) and ganglioside GM3. The specific activities directed toward both substrates were 6.33+/-0.77 and 13.4+/-1.1pmol/mgprotein/min, respectively. Nuclear localization of sialidase activity was confirmed by fluorescent cytochemistry of intact nuclei using 5-bromo-4-chloro-3-indolyl-alpha-D-N-acetylneuraminic acid (X-Neu5Ac) as the substrate. Age-related changes in nuclear sialidase activity in brain tissue were investigated using mice of different ages (i.e. 2-week-, 4-week-, 14-month-, and 26-month-old). Sialidase activity toward 4MU-Neu5Ac had almost identical levels at 2nd and 4th weeks, but thereafter decreased rapidly; the activity at 26 months was about one third of the young levels. Sialidase activity toward GM3 also showed a similar developmental pattern, though the reduction at advancing ages was less than that of activity toward 4MU-Neu5Ac. The present study demonstrates that the activity of nuclear sialidase decreases with aging. The reduced activity of nuclear sialidase may be implicated with alterations of neural cell function during aging.

Differential expression of three sialidase genes in rat development

Mammalian sialidases have been reported to give a great influence on a number of cellular functions including cell differentiation and cell growth by removal of sialic acids from glycoproteins and gangliosides. To understand the roles of the sialidases during development, we investigated expression pattern of three types of sialidase in developing rat brain and liver. For this purpose we cloned a new membrane-associated sialidase cDNA from rat brain. The cDNA encodes 418 amino acids containing three ASP-boxes characteristic of sialidases and the major transcript of 3.5 kb is highly expressed in brain and cardiac muscle but low in liver. Competitive polymerase chain reaction methods were developed to evaluate the mRNA level together with activity assays in comparison with cytosolic and lysosomal sialidases previously obtained. The results indicate that the expression of individual sialidase genes is spatiotemporally controlled with distinct roles in determining the concentration and components of sialo-glycoconjugates during development.

Activity of sialidases in fetal brain axonal growth cones and during postnatal development

In the present work the cytosolic, membrane-bound and the total activities of brain sialidases were measured in fetal axonal growth cone particles and in various brain regions during brain development. The developmental profile showed an important activity in the prenatal and perinatal periods as well as in specific differentiating structures like the axonal growth cones from the fetal brain. Interestingly membrane-bound activity was higher than the cytosolic activity, starting from 50-60% at birth and increasing thereafter. Cytosolic activity was almost at adult levels at birth and did not show a further significant increase thereafter. Our results strongly suggest the commitment of membrane-bound sialidase activity in early neurodifferentiating phenomena like axogenesis, probably regulating the turnover of glycoconjugates like gangliosides at the presynaptic period, since high activity was observed in neuroblast's derived membranes and in the perinatal period.

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.

Biochemical characteristics and subcellular localizations of rat liver neuraminidase isozymes: a paradox resolved

A striking discrepancy in the abilities of two analytical approaches (fluorometric and electrophoretic) to detect the effect of a gene, Neu-2, on rat liver neuraminidase phenotypes led us to examine the biochemical and physical properties of the liver isozymes NEU-1 and NEU-2 that might be responsible for this difference. Cell fractionation via Percoll gradient centrifugation revealed NEU-1 activity almost exclusively in the lysosomal cell fraction, while NEU-2 was strictly cytosolic in distribution. The two isozymes were also found to differ in pH activity curves and optima (optima: 4.6-4.8 and 5.4-5.8 for NEU-1 and NEU-2, respectively) and in solubility characteristics (NEU-2 highly soluble; NEU-1 relatively insoluble but solubilized by freezing/thawing). Both isozymes were found to be freeze-thaw stable in crude, whole-cell extracts, but NEU-1 was destabilized in the enriched (partially purified) lysosomal subcellular fraction. Consideration of these properties relative to those described previously for unidentified cytosolic and membrane bound (lysosomal) rat liver neuraminidases (Tulsiani, D. R. P., and Carubelli, R., J. Biol. Chem. 245:1821, 1970) leads us to believe that NEU-2 also is destabilized by partial purification and that NEU-1 and NEU-2 have very different relative abundances within the cell. The biochemical and physical differences between NEU-1 and NEU-2 can account for the discrepant abilities of the fluorometric and electrophoretic approaches to detect the effects of Neu-2. Ways to increase the sensitivity of the fluorometric approach for quantitative assays of specific NEU-1 and NEU-2 activity are discussed.

Novel alpha-D-mannosidase of rat sperm plasma membranes: characterization and potential role in sperm-egg interactions

During the course of a study of glycoprotein processing mannosidases in the rat epididymis, we have made an intriguing discovery regarding the presence of a novel alpha-D-mannosidase on the rat sperm plasma membranes. Unlike the sperm acrosomal "acid" mannosidase which has a pH optimum of 4.4, the newly discovered alpha-D-mannosidase has a pH optimum of 6.2, and 6.5 when assayed in sperm plasma membranes and intact spermatozoa, respectively. In addition, the two enzymes show different substrate specificity. The acrosomal alpha-D-mannosidase is active mainly towards synthetic substrate, p-nitrophenyl alpha-D-mannopyranoside, whereas the sperm plasma membrane alpha-D-mannosidase shows activity mainly towards mannose-containing oligosaccharides. Evidence is presented which suggest that the sperm plasma membrane alpha-D-mannosidase is different from several processing mannosidases previously characterized from the rat liver. The newly discovered alpha-D-mannosidase appears to be an intrinsic plasma membrane component, since washing of the purified membranes with buffered 0.4 M NaCl did not release the enzyme in soluble form. The enzyme requires nonionic detergent (Triton X-100) for complete solubilization. The enzyme is activated by Co2+ and Mn2+. However, Cu2+ and Zn2+ are potent inhibitors of the sperm plasma membrane alpha-D-mannosidase. At a concentration of 0.1 mM, these divalent cations caused nearly complete inactivation of the sperm enzyme. In addition methyl-alpha-D-mannoside, methyl-alpha-D-glucoside, mannose, 2-deoxy-D-glucose, and D-mannosamine are inhibitors of the sperm surface alpha-D-mannosidase. The physiological role of the newly discovered enzyme is not yet known. Several published reports in three species, including the rat, suggest that the sperm surface alpha-D-mannosidase may have a role in binding to mannose-containing saccharides presumably present on the zona pellucida.

Soluble rat brain sialidase does not influence intracellular glycosylation of Golgi sialyltransferase or its constitutive glycoproteins

Cytosol- and Golgi-enriched fractions were obtained from whole rat brain homogenates by density gradient centrifugation. Using a 4-methylumbelliferyl neuraminic acid substrate a soluble neural sialidase has been identified and characterised. The enzyme had optimal activity at pH 6.0 and a Km of 0.44 +/- 0.18 mM. The specific activity increased during postnatal development and this was in parallel with the described temporal changes in total brain neuraminic acid turnover. The potential of this enzyme to influence the intracellular processing of sialoglycoconjugates was also investigated. Cytosol fractions were incapable of releasing [14C]NeuNAC [( 14C]N-acetylneuramic acid) transferred to the glycoproteins of isolated Golgi membranes by their associated sialyltransferase. Further preincubation of Golgi membranes with soluble sialidase had no effect on their intrinsic sialyltransferase activity. These results demonstrate that no epigenetic regulation of processed sialoglycoconjugates occurs intracellularly and these finding are related to post-translational control of neural cell adhesion molecule (N-CAM) sialylation state.

Characterization and cellular localization of a developmentally regulated rat neural sialidase

A developmentally regulated neural sialidase has been identified in particulate, subcellular fractions of rat brain. Enzyme activity, measured using a [3H]sialoganglioside substrate, was linear with time and had a pH optimum of 4.0-4.5. Protein linearity was only observed at low protein concentrations. This appeared to be caused by enzyme access to a lipophilic substrate, as activity was significantly stimulated by membrane-fluidizing agents. Enzyme activity was developmentally expressed in P2 pellets coincident with in vivo synaptogenesis. It was located on the synaptosome and was particularly high in myelin-containing fractions. Its cellular distribution was confined to neuronal cells and centrally derived oligodendrocytes.

A radiometric assay for ganglioside sialidase applied to the determination of the enzyme subcellular location in cultured human fibroblasts

A radiometric method for the assay of ganglioside sialidase in cultured human fibroblasts was set up. As substrate, highly radioactive (1.28 Ci/mmol) ganglioside GDla isotopically tritium-labeled at carbon C-3 of the long chain base was employed; the liberated, and TLC separated [3H]GM1 was determined by computer-assisted radiochromatoscanning. Under experimental conditions that provided a low and quite acceptable (4-5%) coefficient of variation, the detection limit of the method was 0.1 nmol of liberated GM1, using as low as 10 micrograms of fibroblast homogenate as protein. The detection limit could be lowered to 0.02-0.03 nmol, adopting conditions that, however, carried a higher analytical error (coefficient of variation over 10%). The content of ganglioside sialidase in human fibroblasts cultured in 75-cm2 plastic flasks was 5.8 +/- 2.5 (SD) nmol liberated GM1 h-1 mg protein-1. Subfractionation studies performed on fibroblast homogenate showed that the ganglioside sialidase was mainly associated with the light membrane subfraction that was rich in plasma and intracellular membranes. This subfraction displayed almost no sialidase activity on the artificial substrate 4-methylumbelliferyl-D-N-acetylneuraminic acid. A small but measurable ganglioside sialidase activity was also present in the lysosome-enriched subfraction, which contained a very high sialidase activity on the above artificial substrate. All this supports the hypothesis that human fibroblasts contain sialidases with different subcellular location and substrate specificity. Particularly, the sialidase acting on gangliosides seems to have two sites of subcellular location, a major one at the level of plasma membranes and/or intracellular organelles functionally related with the plasma membranes and a minor one in the lysosomes.

Interactions of pig brain cytosolic sialidase with gangliosides. Formation of catalytically inactive enzyme-ganglioside complexes

Cytosolic sialidase A was extracted from pig brain and purified about 2000-fold with respect to the starting homogenate (about 550-fold relative to the cytosolic fraction). The enzyme preparation provided a single peak on Ultrogel AcA-34 column chromatography and had an apparent molecular weight of 4 x 10(4). On incubation with micellar ganglioside GT1b, (molecular weight of the micelle, 3.5 x 10(5)) under the conditions used for the enzyme assay, brain cytosolic sialidase A formed two ganglioside-enzyme complexes, I and II, which were isolated and characterized. Complex II had a molecular weight of 4.2 X 10(5), and a ganglioside/protein ratio (w/w) of 4:1. This is consistent with a stoichiometric combination of one ganglioside micelle and two enzyme molecules. Complex I was probably a dimer of complex II. In both complexes I and II cytosolic sialidase was completely inactive. Inactivation of cytosolic sialidase by formation of the corresponding complexes was also obtained with gangliosides GD1a and GD1b, which, like GT1b, are potential substrates for the enzyme and GM1, which is resistant to the enzyme action. Therefore, the enzyme becomes inactive after interacting with ganglioside micelles. GT1b-sialidase complexes acted as excellent substrates for free cytosolic sialidase, as did the complexes with GD1a and GD1b.

Sialic acid metabolism in rat liver: effect of carbon tetrachloride

Sialic acid metabolism was investigated in the livers of control rats and of rats treated with a single oral dose (1.5 ml/kg body weight) of carbon tetrachloride. The main change observed during the necrotic stage of CCl4 poisoning (18 h after treatment) was a highly significant reduction in sialyltransferase activity. Slight reciprocal changes in neuraminidase activities, i.e., a small decrease in cytosolic neuraminidase and a small increase in the membrane bound enzyme were also observed. At 72 h after CCl4 treatment, during the stage of liver regeneration, the main change was a marked elevation in membrane-bound neuraminidase (two fold above control values). Moderate increases in the specific activities of CMP-N-acetylneuraminic acid synthetase and sialyltransferase were also observed. A considerable decrease in the sialic acid content of the isolated smooth endoplasmic reticulum (one half of control values) was detected at 72 h after CCl4 administration. The sialic acid content of the rough endoplasmic reticulum, on the other hand, remained at control levels.

Histochemical localization of neuraminidase in the CNS of mice and fish by means of 5-brom-3-indolyl-alpha-ketoside of 5-N-acetyl-D-neuraminic acid (BI-NeuAc)

The applicability of the 5-brom-3-indolyl-alpha-ketoside of N-acetyl-D-neuraminic acid (BI-NeuAc) as substrate for the histochemical indication of neuraminidase (GOSSRAU et al. 1977) was examined in frozen sections of brain, small intestine and kidney from suckling and adult mice and respectively from a cichlid fish (Sarotherodon mosambicus) with and without formaldehyde fixation. Following biochemical investigations using tritiated gangliosides as substrate a decrease in the activity of neuraminidase took place from about 50 to 80% after tissue fixation with formaldehyde. Nevertheless significant histochemical reactions were found only in fixed tissue sections. The specificity of this reaction was shown by means of inhibitions tests using 2,3-dehydro-2-desoxy-N-acetyl-neuraminic acid according to KUMAR et al. (1981). In contrast to distinct staining of neuraminidase activity in the small intestine and kidney, only faint reactions occurred in brain sections. From this it is concluded that the application of the new synthetic substrate for quantitative staining of neuraminidase seems to be not very suitable for the CNS.

Sialic acid metabolism in regenerating rat liver

Sialic acid metabolism was investigated in control rat liver, in regenerating liver at 24 h and 48 h after partial hepatectomy and in the liver of sham-operated animals. High levels of membrane-bound neuraminidase, with no detectable changes in the soluble enzyme, were observed in regenerating rat liver. The neuraminidase activities in the liver of sham-operated rats were identical to those present in control liver. High levels of CMP-N-acetylneuraminic acid synthetase and sialyltransferase were observed both in regenerating liver as well as in the liver of sham-operated rats. The sialic acid content of regenerating rat liver, which was lower than that found in the liver of control and sham-operated rats at 24 h, returned to normal values 48 h after surgery.

Changes in particulate neuraminidase activity during normal and staggerer mutant mouse development

The activity of particulate neuraminidase (sialidase, EC 3.2.1.18) in wild-type mice and the neurological mutant Staggerer was studied during development. Peak activity of this enzyme was observed at postnatal day 3 (P3) in three tissues of normal mice: cerebellum, cerebrum, and liver. In Staggerer, however, neuraminidase peak activity was observed at P27 in the cerebellum, whereas the activity was close to normal in Staggerer cerebrum and liver. Activities of the other glycosidases in Staggerer (alpha-glucosidase (pH 3.7), alpha-glucosidase (pH 6.0), N-acetyl-beta-hexosaminidase, beta-glucosidase, and beta-galactosidase) did not show significant variation compared with wild-type at P27 in any of the three tissues. This indicates that the late activity peak of particulate neuraminidase activity in the Staggerer cerebellum is neuraminidase-specific and not due to a general increase of lysosomal enzymes.

Sialic acid metabolism in rats undergoing chemically-induced mammary gland carcinogenesis in specific dietary states

The enzymes responsible for the activation, transfer and hydrolysis of sialic acids were investigated in female rats with mammary adenocarcinomas induced by administration of a single oral dose (10 mg) of 7,12-dimethylbenz[alpha]anthracene. The carcinogenic process was modulated by the levels and degree of unsaturation of the dietary lipids. Tumor incidence was highest in rats fed a diet containing 20% corn oil, intermediate with 18% coconut oil plus 2% linoleic acid, and lowest in the group receiving a diet with 2% linoleic acid. Sialyltransferase and CMP-N-acetylneuraminic acid synthetase activities were higher in tumors than in control mammary glands. Neuraminidase activity, on the other hand, was higher in control tissue than in tumors. In addition to these tumor-related effects, comparison of the enzyme levels in mammary tissues from control animals of the 3 dietary groups revealed the presence of diet-related effects on sialic acid metabolism. In the livers of tumor-bearing rats, only minor changes of enzyme activities were detected.

Neuraminidase activity in liver and brain from patients with I-cell disease

The activity of neuraminidase in liver and brain from I-cell disease (Mucolipidosis II) was investigated. Neuraminidase activities using two substrates [alpha-L-N-acetylneuraminosyl(2 leads to 3)lactose and alpha-L-N-acetylneuraminosyl(2 leads to 6)lactose] were reduced in the supernatant and sedimentable fractions obtained in isotonic KCl. The activity of beta-D-galactosidase was also reduced in the liver; on the other hand, both neuraminidase fractions were normal, although beta-galactosidase activities were markedly reduced. In view of these results, it is suggested that the defect of neuraminidase is not directly responsible for the primary etiology of I-cell disease.

Beta-D-glucosidase in fractions from rat brain

Beta-Glucosidase activity has been determined in homogenate and in centrifugation fractions of 7-day-old and adult rat brain; maximum activity was found at pH 4 and pH 5. Of the adult brain, more than 50% of the activity was concentrated in the 800-g sediment fraction (P1), while in the brain of 7-day-old rat about 20% was found in the corresponding fraction. The activity maximum in all fractions after a 2% Triton X-100 treatment occurs at pH 5. Addition of Triton to adult brain homogenate enhances the activity, but this stimulation is less than the sum of the activities observed at pH 4 and pH 5 in the absence of Triton. Triton addition to brain homogenate of 7-day-old rat results in a fall in activity at pH 4 and in a maximum at pH 5. In rat brain homogenate subjected to sonication, a loss of activity is observed at pH 4, scarcely at pH 5; the activity loss is completely abolished and turned into an increase under the influence of Triton. This increase equals the level obtained when Triton is added to an untreated brain homogenate. Sonication of rat brain homogenate leads to changes in the distribution pattern; about 25% of the activity of the adult brain is found in the P1 fraction compared to 50% in the corresponding fraction of the untreated brain. Fractionation of a sonicated brain homogenate from adult rat reveals that at pH 4 most activity (52%) is concentrated in the 20,000-g pellet (P2), 23% in supernatant fluid (S2); at pH 5 the opposite is observed; most activity (49%) is found in the 20,000-g supernatant (S2) and 23% in the 20,000-g pellet (P2). In the presence of Triton the activity of the sonicated brain homogenate of adult rat increases; this stimulation roughly equals the sum of the corresponding activities measured at pH 4 and pH 5 in the absence of Triton.

Studies on brain cytosol neuraminidase. II. Extractability, solubility and intraneuronal distribution of the enzyme in pig brain

The origin and properties of cytosolic neuraminidase (acylneuraminyl hydrolase, EC 3.2.1.18) from pig brain were studied. 1. The brain extracts containing the cytosol derived from neuronal bodies and glial cells carry 0.69 munits neuraminidase/g fresh tissue. The behaviour of neuraminidase during extraction closely paralleled that of authentic cytosolic enzyme, lactate dehydrogenase; whereas, it differed from that of the lysosomal enzymes, beta-hexosaminidase and beta-galactosidase, also found in the extracts. 2. Nerve endings from either crude or purified preparations, when treated by hypoosmotic shock, released neuraminidase activity up to a maximum of 1.25 munits/g fresh tissue. The behaviour of releasable neuraminidase was always identical to that of lactate dehydrogenase and very similar to that of ATPase and acetylcholinesterase. Typical lysosomal enzymes, however, such as beta-galactosidase and beta-hexosaminidase, behaved differently under the same conditions. This neuraminidase activity is thought to be derived from the cytosol of nerve endings. 3. The specific activity of neuraminidase in nerve-ending cytosol is 15--20 times that in neuronal body and glial cell cytosol. Some properties (pH, Km value, V/t relationship) of the cytosolic enzymes of different origin are similar; others (stability on standing at 4 degrees C; resistance to freezing and thawing) are different. Hypoionic solutions caused both cytosolic neuraminidases to slowly precipitate and to assume a stable insoluble form which was still active.

Effect of acute ethanolic intoxication on the neuraminidase activity of rat liver Golgi apparatus

Neuraminidase and galactosyltransferase were investigated in total Golgi appartus and in the three fractions of increasing densities (GF1, GF2, and GF3) isolated from the microsomal fraction of rat liver homogenates by flotation in a discontinuous sucrose density gradient (Ehrenreich, J.H., Bergeron, J.J.M., Siekevitz, P. and Palade, G.E. (1973) J. Cell Biol. 59, 45-72). About 50% decreases in neuraminidase content (units/g liver) and specific activity (units/mg protein) were observed in total Golgi as well as in the three fractions isolated at 45 min, 90 min, 180 min and 16 h after administration of a single oral dose of 50% aqueous ethanol (0.6 g/100 g body weight). Colchicine administration (introperitoneal injection, 0.5 mg/100 g body weight) caused a similar loss of neuraminidase activity; however, the effect of ethanol plus colchicine was not additive. Golgi galactosyltransferase, on the other hand, experienced marked increases of activity following ethanol administration but, unlike the results reported by others (Gang, H., Lieber, C.S. and Rubin, E. (1973) Nat. New Biol. 243, 123-125), significant increases in total activity and specific activity were already quite evident at 90 min after ethanol ingestion. In contrast with the decreased values observed in Golgi, the total particle-bound neuraminidase was significantly elevated following ethanol administration. Ultrastructural studies revealed increased lysosomal content and detachment of polysomes from the rough endoplasmic reticulum. A model, which takes into account these enzymological and ultrastructural findings and their biological significance, is proposed.

Interaction between the soluble and particulate neuraminidases of chick liver

The sum of the neuraminidase activities found in the isolated soluble and particulate fractions of chick liver was considerably higher than that observed in the cytoplasmic extract from which these fractions were obtained. Addition of increasing amounts of particulate neuraminidase to a constant amount of the soluble preparation resulted in a progressive loss of enzyme activity.

Brain neuraminidases and gangliosides

A number of data of kinetics nature indicate that brain neuraminidases (the cytosol and the membrane bound enzyme) recognize the physical state of gangliosidic substrate, with immediate modification of the activity. The interactions between the enzyme(s) and the different physical forms of the substrate are still to be studied at the molecular level. The knowledge of these phenomena would greatly help understanding the role played by gangliosides in the neuronal plasma membrane.

Studies on brain cytosol neuraminadase. I. Isolation and partial characterization of two forms of the enzyme from pig brain

1. Two forms of cytosol neuraminidase (EC 3.2.1.18) (neuraminidase A and neuraminidase B) were isolated and purified from pig brain homogenate, by proceeding through the following steps: centrifugation of brain homogenate at 105 000 X g (1h); ammonium sulphate fractionation (35-55% saturated fraction); column chromatography on Biogel A 5 m; column chromatography on hydroxy apatite/cellulose gel; affinity chromatography on Affinose-tyrosyl-p-nitrophenyloxamic acid. The separation of the two forms of neuraminidase was provided by chromatography on hydroxylapatite/cellulose gel. Neuraminidase A was purified about 500-fold; neuraminidase B about 400-fold. 2. The pH optima and the maximum activities in various buffers were different for neuraminidase A and B (for instance the pH optimum was in sodium acetate/acetic acid buffer, 4.7 for neuraminidase A and 4.9 for neuraminidase B). Ions affected in a different way the two enzymes: K+ activated neuraminidase A but not neuraminidase B; Na+ and Li+ inhibited neuraminidase A at a higher degree than neuraminidase B. Neuraminidase B seemed to be moderately activated by some bivalent cations (Ca2+; Mg2+; Zn2+); neuraminidase A did not. The Km values for sialyllactose were different: 2.2-10(-3) M for neuramindase A; 0.46-10(-3) M for neuraminidase B.