Intracellular Location and Properties of Bovine Brain Sialidase

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.

Properties of endogenous, membrane-associated sialidase activity (N-acetylneuraminidase) of the goldfish visual system

The endogenous sialidase (N-acetylneuraminidase) activity of membranes prepared from goldfish retina and optic tectum displays characteristics similar to those reported for neural plasma membrane sialidases of other organisms. Endogenous membrane sialidase activity was found to be optimal at ph 4.0, and maximal release was obtained at 37-50 degrees C, above which temperature thermal instability of the preparations was observed. Optic nerve crush, which results in regeneration of retinal ganglion cell axons, did not result in significant changes in measured endogenous membrane sialidase activity in either the retina or the optic tectum. Enzymatic hydrolysis of membrane sialoglycolipid (ganglioside) accounted for about 70% of the total sialic acid released. Ganglioside GM1 accumulated as the major lipid product in both retina and tectum, indicating that the inner sialosylgalactosyl linkage in the ganglio oligosaccharide series was resistant to hydrolysis by the endogenous enzyme.

The effect of early postnatal undernutrition on the growth and development of the rat brain

1. Rat pups were undernourished during the period of the brain growth-spurt by feeding their mothers a low-protein diet from the third day post partum. 2. The pups were killed on days 5, 6, 9, 12, 16, 20 and 24 post partum, and their brains were analysed for protein, DNA, glycosides and glycoproteins. The activities of four enzymes involved in neurotransmission, and in the synthesis of glycolipids and myelin were also measured. Results of the analyses were compared with those obtained for pups that were suckled by well-nourished dams. 3. The brains of the undernourished pups contained substantially less protein and DNA; gangliosides and glycoproteins were also reduced. 4. All four enzymes showed lower peak activities in the nutritionally deprived animals, and the attainment of peak activity was retarded by several days. 5. These results suggest that undernutrition imposed during the brain growth-spurt leads to a deficit in the glial cell population and thus in the capacity to form myelin, and reduced development of cellular processes.

Studies on the mechanisms of the epileptiform activity induced by U186661. I Gross alteration of the lipids of synaptosomes and myelin

U18666A, an inhibitor of desmosterol reductase (a terminal enzyme in cholesterol synthesis), has been found to produce chronic epileptiform activity in laboratory animals. Since desmosterol might substitute for cholesterol in neuronal membranes without detriment, the present study was undertaken to examine the possibility that this drug-induced epilepsy was related to changes in other brain lipids. Chronic treatment of rat with U18666A, beginning at one day of age, resulted in pronounced decreases in the concentration of phospholipids and increases in gangliosides of brain microsomal, synaptosomal, and crude myelin fractions. Since total sterol levels were not changed, the ratio of sterols to phospholipids also increased. If drug treatment was stopped at 4 weeks of age, brain lipids of all subcellular fractions examined returned to normal levels by 8 weeks, and no epileptiform activity was detected. However, following 8 weeks of continuous treatment, epileptiform activity was present, and the changes in brain lipids were focused in the myelin fraction. Phospholipid levels and the sterol:phospholipid ratio of microsomes and synaptosomes, in contrast to myelin, were near normal; however, gangliosides were still clearly elevated in all fractions. A reported ability to induce epileptiform activity in rats by treatment with antiserum to brain gangliosides could indicate a special significance of the altered myelin and synaptic gangliosides to the U18666A-induced epilepsy. We suggest that some epileptiform conditions could be directly related to alterations in the lipid composition of critical neuronal structures.

The organization of gangliosides and other lipid components in synaptosomal plasma membranes and modifying effects of calcium ion

Synaptosomes were prepared from bovine brain by zonal rotor sucrose density centrifugation. While a major fraction of lipid-bound sialic acid is included uniformly within the synaptosomal distribution profile, the sialoglycoproteins and some gangliosides do not follow this pattern. Exposure to extrasynaptosomal calcium results in alterations in the surface labeling properties of some gangliosides and membrane plasmalogens, suggesting that extrasynaptic Ca2+ may influence the conformation of complex lipids in synaptic plasma membranes. The level of intrinsic membrane-associated sialidase activity that liberates sialic acid from these sialoglycoconjugates parallels the synaptosomal buoyant density distribution profile, supporting a view that this enzyme resides in synaptosomal membranes in close association with a sialolipid substrate.

Chloroquine intoxication induces ganglioside storage in nervous tissue: a chemical and histopathological study of brain, spinal cord, dorsal root ganglia, and retinal in the miniature pig

The effect of chronic chloroquine intoxication on lipid composition, particularly the gangliosides, was studied in the nervous system of miniature pigs, type Göttingen. The tissues examined were cerebrum, spinal cord, dorsal root ganglia and retina. Chloroquine was given in the diet in doses of 2.0-3.5 g/kg good. The intoxication of the pigs was started at the age of 100-240 days and continued for 177-219 days. The control pigs received the same diet without chloroquine. The ganglioside concentration was increased in all the tissues examined. Dorsal root ganglia and retinal were the tissues affected most and showed a twofold increase. This corresponded to the light and electron microscopically demonstrated extensive storage process in the perikarya of dorsal root ganglion cells and inner ganglion cells of the retinal. Under light microscopy the storage material was granular, intensely PAS-positive and dissolved by paraffin embedding. The electron microscopical equivalent consisted of conglomerates of membranous lysosomal residual bodies. In cerebrum the ganglioside concentration was increased by 12%. Storage in the brain varied widely between different systems and types of cells. The allocortex was much more affected than the isocortex. Certain inhibitory ganglion cell types, such as the basket cells, exhibited the most massive storage of all. The spinal medulla was morphologically less involved but showed approximately the same ganglioside increase, though not statistically significant. With the exception of cerebrum the increase in the tissues examined involved all the individual gangliosides, most severely ganglioside GM2 and three fucogangliosides. In cerebrum only the ganglioside GM2 was increased more than the other gangliosides. Chloroquine intoxication did not affect the concentration of phospholipids or cholesterol in the cerebrum, spinal cord or dorsal root ganglia, but in retina the acidic phospholipids were significantly increased.

Effects of essential fatty acid deficiency during late gestation on brain N-acetylneuraminic acid metabolism and behaviour in the progeny

1. Rat dams given a diet containing 100 g maize oil/kg for approximately two weeks before mating and during the first 14 d of gestation, were given the same diet or one containing 100 g hydrogenated coconut oil/kg (essential fatty acid (EFA)-deficient) in place of maize oil until parturition. After parturition the dams were given the same diets and all progeny were weaned to the maize oil diet at 21 d of age. Brain N-acetylneuraminic acid (NeuNAc) content as well as neuraminidase (sialidase; (EC 3.2.1.18), and cytidine monophosphate N-acetylneuraminic acid synthetase (CMP-NeuNAc synthetase) activities were measured at days, 7, 14, 21 and 168 in the progeny. Y-maze learning was measured at 168 d. 2. Brain weight was independent of dietary fat at all ages. 3. Lack of EFA in the maternal diet during gestation and lactation depressed ganglioside and glycoprotein NeuNAc levels and the activities of sialidase and CMP-NeuNAc synthetase. 4. Maternal dietary deprivation of EFA irreversibly impaired learning behaviour of the progeny. A relationship exists between early exposure to EFA deficiency and learning potential of the progeny.

[Lipid-protein interactions: mechanisms of enzymatic glycolipid catabolism and their genetic restrictive escapes]

Investigations of the genetic basis of ganglioside catabolism have led to the characterisation of two types of lipid-enzyme interaction: a) Breakdown of membrane-bound glycolipids as far as catalysed by membrane-bound enzymes is regulated by the membrane itself. b) The degradation of micelle-forming glycolipids by water-soluble lysosomal enzymes is facilitated by cofactors known as activator proteins. A genetic defect in an activator protein can be just as fatal as the lack of the enzyme itself.

Blocking action of intracellularly injected neuraminidase on central synapses in vivo

The effect of neuraminidase on synaptic transmission was studied at cholinergic and noncholinergic contacts in the buccal and cerebral ganglion of Ap]lysia. The amplitudes of monosynaptic unitary postsynaptic potentials generated by intracellular stimulation of identified presynaptic neurones were measured as indication for the efficacy of synaptic transmission. Neuraminidase was either intrasomatically injected into a presynaptic neurone, or the whole ganglion was incubated with the enzyme. Intrasomatic injection of the enzyme resulted in complete failure of synaptic transmission. This effect occurred independently of the transmitter used. The synaptic failure was presynaptic in origin. The biophysical characteristics of an injected neurone, particularly the amplitude and propagation of its action potential, did not appear to be affected by neuraminidase. Synaptic transmission and biophysical membrane properties were unaffected by extracellular neuraminidase. We conclude that the synaptic blockade is due to the enzyme's action inside the presynaptic nerve ending. It seems most likely that neuraminidase cleaves sialic-acid-containing-compounds associated with the nerve terminal surface membrane, probably thus causing failure of transmitter release.

The subcellular biochemistry of thyroid

In this review the subcellular localization of enzymes and constituents in thyroid is discussed. Conditions and results of differential pelleting and gradient centrifugation studies are described with special attention to the validity of the markets used (Table VI). Special approaches to the isolation and characterization of thyroid organelles and membranes are extensively reviewed (Table VII). Subcellular fractionation of thyroid tissue has been shown to be an arduous task. Classic approaches for differential pelleting and gradient centrifugation, which have been proved successful for rat liver, are not always equally satisfactory for thyroid. The major problem is the toughness of the tissue requiring rather traumatizing homogenizing procedures. Nevertheless, the fractionation procedures did allow the subcellular localization of some enzymes and constituents to be established with a high degree of certainty. Furthermore, enriched subcellular fractions have been isolated which have been useful for biochemical studies concerning the specific function of this tissue.

Large-scale preparation of synaptosomes from bovine brain using a zonal rotor technique

A zonal rotor technique for the preparation of synaptosomes in bulk from bovine brain frontal cortex based on an impirical transformation of a small-volume discontinuous sucrose density gradient arrangement is presented in detail. The procedure yields new information concerning synaptosomes prepared in sucrose gradients. Cerebroside analysis and electron microscopy show myelin contamination to be restricted to the leading, less dense edge of the synaptosomal profile, free mitochondria to the trailing, more dense edge. Exclusion of fringe areas yields a highly purified synaptosome preparation which entirely enters the next dense layer beyond the 0.8 : 1.2 M sucrose interface. This interface collects most of the oubain-sensitive (Na+, K+) adenosine triphosphatase activity. The purified synaptosomes display very high intrinsic sialidase activity and are rich in di-, tri-, and tetrasialogangliosides, the preferred substrates for the enzyme. Up to 90% of the cholinesterase activity in the zonal rotor synaptosome preparation is specific acetylcholinesterase.

Distribution in spleen subcellular organelles of sialidase active towards natural sialogylcolipid and sialoglycoprotein substrates

A procedure was devised for the preparation of enriched populations of subcellular organelles from homogenized bovine spleen. The fractions obtained were characterized for arylsulfatase, succinate dehydrogenase, UDPgalactosyltransferase and 5'-nucleotidase activities. The distribution of sialidase (acylneuraminyl hydrolase, EC 3.2.1.18) activity directed towards either endogenous substrate or exogenous ganglioside substrate suggests that it is enriched in the plasma membrane/microsomal fractions. Sialidase activity towards exogenous sialoglycoproteins, isolated from erythrocyte membrane, was enriched in the least dense of the plasma membrane/microsomal-containing fractions. The endogenous sialidase substrates were primarily the sialoglycolipids, hematoside and disialogangliosides. At the pH optimum, 3.8, and 37 degrees C, release of endogenous sialic acid was linear with time for 3 h. At the end of this time, 85% or more of the available endogenous substrate was hydrolyzed.

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.

Protein and glycoprotein composition of subsynaptosomal fractions. Implications for Exocytosis and recycling of synaptic vesicles

Highly enriched fractions of synaptic junctional complexes, synaptic vesicles, and coated vesicles were isolated from rat forebrains and compared, along with synaptosomal plasma membrane and its nonjunctional components, by discontinuous sodium dodecylsulfate-polyacrylamide gel electrophoresis. When stained for proteins with Coomassie blue, the gels all contained the same protein bands, only in different relative amounts. Mixing experiments revealed no additional bands. However, gel patterns of each fraction were not only quantitatively but also qualitatively different when stained for carbohydrate. These observations suggested that some of the protein bands may vary in their degree of glycosylation among the various synaptic fractions. Within the limits of resolution of the methods used here, these results are consistent with the morphological process of synaptic vesicle exocytosis and recycling but suggest the possibility of a reversible modification of certain membrane glycoproteins as they pass through the various membrane compartments.

Effect of neurotoxic divalent cations on the activity of the intrinsic nerve ending membrane-associated sialidase of bovine brain

Exposure to Hg2+ below 10 micrometer destroys synaptosomal membrane-associated sialidase of bovine brain in situ. Inhibition by Cu2+ occurs only at relatively higher concentrations, and is demonstrable after the synaptosomal membrane preparation has been presaturated with Cu2+ . Pb2+ does not inhibit enzymatic activity. Hg2+ does not exert a significant effect on the free energy of association of monomeric brain gangliosides into aggregates, or on the stability of the aggregate forms, as estimated by ultracentrifugal analysis of the ion-independent moment of ganglioside micelles as a function of concentration. Hg2+ inhibits synaptic membrane sialidase acting both in situ on the native sialocompounds in the membrane, or on exogenous ganglioside. Kinetic analyses of the exogenous activity in membranes exposed to Hg2+ reveal lowered Vmax values but no substantial change in Km for synaptosomal membrane gangliosides. These findings suggest that the powerful inhibitory effect exerted by Hg2+ on nerve ending membrane sialidase is enzyme directed, not substrate directed. It may be postulated that part of the neurotoxic effect of low levels of Hg2+ stems from an interference with synaptic metabolism by the destruction of membrane-associated sialidase. This enzyme can serve the purpose of modulation of synaptic negative charge density by releasing bound, strongly anionic, sialic acid from highly concentrated sialocompounds in the membrane.

Studies on bovine brain membrane-bound neuraminidase (sialidase)

1) Lipophilic ganglioside GD1a (IV3NeuAc, II3NeuAc-GgOse4-Cer) is taken up by the cell membranes and hydrolyzed faster by membrane-bound neuraminidase than are water soluble substrates of the enzyme. 2) The enzymic breakdown of ganglioside GD1a is enhanced by general anesthetics whereas the degradation of the hydrophilic substrate sialyllactitol is reduced by these same agents. 3) General anesthetics lower the microviscosity of membranes as indicated by studies of fluorescence depolarisation with the indicator 1,6-diphenylhexatrien. Decreased microviscosity can result in a higher lateral diffusion of ganglioside GD1a, increasing its interaction with membrane-bound neuraminidase. 4) In vitro studies indicate that the activity of membrane-bound neuraminidase on gangliosides of brain membranes is regulated by the viscosity of these membranes and their monosialoganglioside content.

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.

Biochemical evidence on the role of gangliosides in nerve-endings

From the biochemical and developmental data in the literature, there appears to be some specific relationship of gangliosides to synapses. Whether the concentration of polysialo-gangliosides is located in the immediately pre-synaptic part of the neuronal plasma membrane is not known. There are many unanswered questions about the gangliosides, which we have attempted to pose in this article. There are as many hypotheses about roles for gangliosides, and virtually no data to back them up. In fact there are not even real indications of possible functions. We believe that it will be very difficult to define the functions of gangliosides until more of the basic questions are answered-even if their synaptic localization is a constant temptation to speculate.

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.