Synthesis and turnover of cerebroside sulfate of myelin in adult and developing rat brain

Age- and brain region-specific effects of dietary vitamin K on myelin sulfatides

Dysregulation of myelin sulfatides is a risk factor for cognitive decline with age. Vitamin K is present in high concentrations in the brain and has been implicated in the regulation of sulfatide metabolism. Our objective was to investigate the age-related interrelation between dietary vitamin K and sulfatides in myelin fractions isolated from the brain regions of Fischer 344 male rats fed one of two dietary forms of vitamin K: phylloquinone or its hydrogenated form, 2',3'-dihydrophylloquinone (dK), for 28 days. Both dietary forms of vitamin K were converted to menaquinone-4 (MK-4) in the brain. The efficiency of dietary dK conversion to MK-4 compared to dietary phylloquinone was lower in the striatum and cortex, and was similar to that in the hippocampus. There were significant positive correlations between sulfatides and MK-4 in the hippocampus (phylloquinone-supplemented diet, 12 and 24 months; dK-supplemented diet, 12 months) and cortex (phylloquinone-supplemented diet, 12 and 24 months). No significant correlations were observed in the striatum. Furthermore, sulfatides in the hippocampus were significantly positively correlated with MK-4 in serum. This is the first attempt to establish and characterize a novel animal model that exploits the inability of dietary dK to convert to brain MK-4 to study the dietary effects of vitamin K on brain sulfatide in brain regions controlling motor and cognitive functions. Our findings suggest that this animal model may be useful for investigation of the effect of the dietary vitamin K on sulfatide metabolism, myelin structure and behavior functions.

Layer-specific sulfatide localization in rat hippocampus middle molecular layer is revealed by nanoparticle-assisted laser desorption/ionization imaging mass spectrometry

Lipids are major structural component of the brain and play key roles in signaling functions in the central nervous system (CNS), such as the hippocampus. In particular, sulfatide is an abundant glycosphingolipid component of both the central and the peripheral nervous system and is an essential lipid component of myelin membranes. Lack of sulfatide is observed in myelin deformation and neurological deficits. Previous studies with antisulfatide antibody have investigated distribution of sulfatide expression in neurons; however, this method cannot distinguish the differences of sulfatide lipid species raised by difference of carbon-chain length in the ceramide portion in addition to the differences of sulfatide and seminolipid. In this study, we solved the problem by our recently developed nanoparticle-assisted laser desorption/ionization (nano-PALDI)-based imaging mass spectrometry (IMS). We revealed that the level of sulfatide in the middle molecular layer was significantly higher than that in granule cell layers and the inner molecular layer in the dentate gyrus of rat hippocampus.

Metachromatic leukodystrophy: genetics, pathogenesis and therapeutic options

Metachromatic leukodystrophy is a lysosomal storage disease caused by the deficiency of arylsulphatase A (ASA). This leads to storage of the membrane lipid sulphatide, which is abundant in myelin. A pathological hallmark of the disease is demyelination, causing various and ultimately lethal neurological symptoms. Today more than 110 mutations in the ASA gene have been identified, of which only three are frequent. Patients homozygous for alleles, which do not allow for the synthesis of functional ASA always suffer from the severe form of the disease, whereas alleles allowing the expression of residual enzyme activity are associated with the later onset juvenile or adult forms of metachromatic leukodystrophy. In addition, there are other as yet unknown genetic or epigenetic factors modifying the phenotype substantially. ASA-deficient mice have been generated as a model of metachromatic leukodystrophy. These mice store sulphatide and show progressive neurological symptoms, but do not demyelinate. This animal model was recently improved using a transgenic approach, which generated mice in which sulphatide synthesis in myelin-producing cells is enhanced. This new animal model reflects the pathological characteristics of the human disease. ASA-deficient mice have been used in various therapeutic trials involving enzyme replacement, haematopoietic stem-cell-based gene therapy and direct injections of ASA-expressing viral vectors into the brain. These animal studies have paved the way for future clinical studies of enzyme replacement and gene therapy.

CONCLUSION

For many years this devastating disorder was considered untreatable and the outlook for patients was poor. Within a comparatively short period of time since the ASA gene was cloned in 1989, genetic and biochemical studies and data generated from newly developed animal models have led to the first clinical trials. It is hoped that these developments will prove beneficial for patients.

Metabolism of sulfolipids in isolated renal tubules from rat

Proximal-rich tubules were prepared from rat kidneys by using collagenase treatment. The isolated rat renal tubules were compared with the intact kidney on the following characteristics. (1) Composition of the sulfoglycolipid. (2) Sulfoglycolipid metabolism based on incorporation of [35S]sulfate or some properties of sulfoglycolipid metabolism, including the activities of anabolic and catabolic enzymes. The results indicated following characteristics of the isolated renal tubules in comparison to the kidney in vivo. (1) The sulfoglycolipid compositions are qualitatively similar, except that the content of glucosyl sulfatide, Gg3Cer II3-sulfate, and GM4 was slightly higher in the isolated tubules. (2) The apparent half-lives (15-55 min) of sulfoglycolipids in the isolated tubules could indicate the existence of a rapid turnover pool of these lipids. (3) The sulfotransferase and sulfatase activities related to sulfoamphiphiles in the renal tubule were similar to those reported for the whole kidney. Based on the above criteria, we conclude that the isolated rat renal tubule should be a useful metabolic system for clarification of the short-term physiological events, up to 90 min, of proximal tubular sulfoglycolipids. By using the present system, we showed that biosynthesis of the renal total sulfoglycolipid was significantly elevated in rats deprived of water for 24 h.

Menaquinone-4 concentration is correlated with sphingolipid concentrations in rat brain

Studies with animals support a role for vitamin K (VK) in the biosynthesis of sphingolipids, a class of complex lipids present in high concentrations in the brain. In mice and rats, VK deficiency decreases levels of brain sulfatides and causes behavioral alterations. In light of its heterogeneity and to better understand the role of VK in the brain, we characterized the distribution of the two main VK vitamers, phylloquinone (K1) and menaquinone-4 (MK-4), in nine distinct brain regions. Weaning female Sprague-Dawley rats (n=5/dietary group) were fed diets containing either low (L, 80 microg/kg diet), adequate (A, 500 microg/kg diet) or high (H, 2000 microg/kg diet) levels of K1 for 6 mo. The main form of VK in the brain was MK-4, and it was present in significantly higher concentrations in myelinated regions (the pons medulla and midbrain) than in nonmyelinated regions. Both regional K1 and MK-4 increased with K1 intake (P<0.05). Sphingolipid distribution varied across brain regions (P<0.001) but was not affected by K1 intake. In the L and A groups but not the H group, brain MK-4 concentration was positively correlated with the concentrations of sulfatides (L, r=0.518; A, r=0.479) and sphingomyelin (L, r=0.515; A, r=0.426), and negatively correlated with ganglioside concentration (L, r=-0.398); A, r=-0.353). Sphingolipids are involved in major cellular events such as cell proliferation, differentiation and survival. The strong associations reported here between brain MK-4 and sphingomyelin, sulfatides and gangliosides suggest that this vitamer may play an important role in the brain.

Galactolipids are molecular determinants of myelin development and axo-glial organization

Myelination is a developmentally regulated process whereby myelinating glial cells elaborate large quantities of a specialized plasma membrane that ensheaths axons. The myelin sheath contains an unusual lipid composition in that the glycolipid galactosylceramide (GalC) and its sulfated form sulfatide constitute a large proportion of the total lipid mass. These glycolipids have been implicated in a range of developmental processes such as cell differentiation and myelination initiation, but analyses of mice lacking UDP-galactose:ceramide galactosyltransferase (CGT), the enzyme required for myelin galactolipid synthesis, have more recently demonstrated that the galactolipids more subtly regulate myelin formation. The CGT mutants display a delay in myelin maturation and axo-glial interactions develop abnormally. By interbreeding the CGT mutants with mice that lack myelin-associated glycoprotein, it has been shown that these specialized myelin lipids and proteins act in concert to promote axo-glial adhesion during myelinogenesis. The analysis of the CGT mutants is helping to clarify the roles myelin galactolipids play in regulating the development, and ultimately the function of the myelin sheath.

L-cycloserine slows the clinical and pathological course in mice with globoid cell leukodystrophy (twitcher mice)

Globoid cell leukodystrophy (Krabbe's disease) is an autosomal recessive disease that affects the lysosomal enzyme galactosylceramidase. Galactosylceramidase removes galactose from galactosylceramide and psychosine, which are derived from sphingosine. In the present study, L-cycloserine (an inhibitor of 3-ketodyhydrosphingosine synthase) was administered to the twitcher mouse, an authentic model of globoid cell leukodystrophy. Twitcher mice treated with L-cycloserine had a significantly longer life span and a delayed onset of weight loss than vehicle-injected twitcher mice. Pathological features such as macrophage infiltration and astrocyte gliosis also were less in treated twitcher mice. These results indicate that substrate reduction therapy may have therapeutic value for individuals with residual enzymatic activity, e.g., individuals with late onset disease or individuals with partial enzyme replacement via bone marrow transplantation. In these cases, a reduction in galactosylceramide and psychosine synthesis would enable residual enzymatic activity to keep up with the accumulation of these substrates that would otherwise lead to pathology.

Sulfoglycolipids bind to adhesive protein amphoterin (P30) in the nervous system

HNK-1 antibody reactive carbohydrate epitope carried by glycolipids and glycoproteins has been shown to be involved in cell to cell interactions. It has been proposed that the HNK-1 reactive 3-sulfoglucuronyl carbohydrate epitope in glycolipids may interact with a cell surface receptor to promote the biological response in the developing nervous system. The possible occurrence of such a receptor was examined in rat nervous system. A specific binding of sulfoglycolipids to a 30 kD protein from adult rat cerebellum is described. Little binding was found with neutral glycolipids and gangliosides. The 30 kD protein from cerebellum was partially purified on a sulfatide-octyl-Sepharose affinity column. Binding of sulfoglucuronyl glycolipids to a similar 30 kD protein from forebrain previously identified as amphoterin is also shown. Amphoterin is developmentally regulated and is involved in neural cell adhesion and neurite extension.

In vivo metabolism of fluorescent ceramide in central nervous system myelin of adult rats

The metabolism of sphingolipids in the central nervous system (CNS) has been studied in adult rats by intraventricular administration of fluorescent ceramide (CER). Rats were sacrificed at various time points post inoculation and the fluorescence of CER, cerebrosides (CB), sulfatides (SULF) and sphingomyelin (SPM) was determined in the CNS myelin and in the pellet, containing mainly microsomes, obtained by Norton myelin preparation. The incorporation of fluorescence was more in the pellet than in the myelin at all times studied. Initially the fluorescence present in the pellet was prevalently due to untransformed CER but an increase of fluorescent products with time was observed. CB was the main product up to 2 h post inoculation, then it decreased with concomitant increase of fluorescent SULF. In the myelin we did not observe differences in incorporation and transformation of fluorescent CER with time: CB was the main fluorescent product at all times studied. At 0.5 h post inoculation the fluorescence, observed by fluorescence microscope, was located in the cell lining the ventricles while after 24 h it appeared also in the paraventricular areas.

Effect of neonatal undernutrition upon cerebroside sulfate degradation in the developing rat brain

In order to find out if the decreased accumulation of cerebroside sulfates observed in 21-d-old undernourished rats was in part the result of an increased rate of catabolism of these galactolipids, the in vivo degradation of brain cerebroside sulfates was studied in 18-d-old normal and undernourished rats. Two hours after the intracranial injection of the precursor (0 time), the animals were injected intraperitoneally with unlabeled sodium sulfate. Labeled cerebroside sulfates were measured in the brain up to 48 h after the chase. In normal animals, the radioactivity decreased at 24 h and 48 h to 55% and 41%, respectively, of the value obtained at 0 time. In undernourished animals, degradation was negligible, since the radioactivity attained at 0 time remained almost constant up to 48 h. The lack of in vivo degradation of cerebroside sulfates observed in the starved rats cannot be explained by a deficiency of Arylsulfatase A, since the pattern of activity of the enzyme was similar in both groups of animals.

Galactosylceramide sulfotransferase, arylsulfatase A and cerebroside sulfatase activity in different regions of developing rat brain

The in vivo metabolism of sulfatides was studied in spinal cord and cerebral cortex of developing rat pups. Developmental changes in the rate of sulfolipid synthesis were measured after the intraperitoneal injection of 35SO4(2-). We also measured the accumulation of sulfatides, as well as the profiles of cerebroside sulfotransferase, cerebroside sulfatase and arylsulfatase A in both brain regions as a function of postnatal development. The accumulation of sulfatides was higher in spinal cord than in cerebral cortex. In addition, sulfatide metabolism was more active in spinal cord. In both brain regions, the developmental pattern of 35SO4(2-) incorporation into sulfolipids was closely correlated to the activities of cerebroside sulfotransferase and of arylsulfatase A. The activity of these enzymes was initially low, increased during the period of active myelination and declined thereafter. However, the activity of cerebroside sulfatase, measured with its physiological substrate, [35S]sulfatide, increased during development and did not decline. An explanation for the difference between the developmental profiles of the arylsulfatase A and cerebroside sulfatase reactions (which are supposed to be catalysed by the same enzyme) is proposed.

Studies on the submicrosomal fractions of bovine oligodendroglia: lipid composition and glycolipid biosynthesis

Oligodendroglia were isolated from bovine brain, and a "crude" microsomal fraction obtained from cell homogenates was subfractionated into myelin (MP), plasma membranes (PM), Golgi (GF), smooth (SER) and rough (RER) endoplasmic membranes using discontinuous-sucrose gradient centrifugation. The submicrosomal fractions were characterized by ultrastructural examination and analysis of the specific organelle markers. The myelin and plasma membrane rich fractions contained characteristically the highest amounts of the lipid with lower mole percentages of total phospholipids and phosphatidylcholine, and higher concentrations of phosphatidylethanolamine (+ plasmalogens), cholesterol and galactolipids. Considerable amounts of the typical myelin galactolipids (galacto-cerebrosides, sulfatides and monogalactosyl diglycerides) were also found in the Golgi fraction (GF). The GF fraction had the greatest enrichment of glycolipid-forming galactosyltransferases, and the distribution of these enzymes correlated well with that of the Golgi marker enzymes. The results give evidence that intracellular Golgi apparatus of oligodendroglia is rich in the myelin-specific lipids, and suggest its involvement in the synthesis and processing of myelin lipids.

[Perspectives in the use of NMR for the biochemical study of the white matter of the brain]

This paper presents a survey of the function and the biochemical composition of the myelin sheath. Proton nuclear magnetic resonance spectroscopy of extracts of human white matter tissue is a major method for the identification of myelin constituants. We present results of some experiments obtained with normal brain material at 80 MHz and 400 MHz.

Regulation of cerebroside and sulfatide metabolism in glia cells

Mouse oligodendroglioma cells, G-26 clone 20 and 24, contain galactosylceramide (cerebroside) and sulfogalactosylceramide (sulfatide) as determined by an HPLC technique. The synthesis of both these lipids was stimulated by 10(-6) M hydrocortisone (cortisol) and also by the removal of serum from the culture medium. Forty-eight hours after the addition of cortisol the incorporation of H235SO4 into sulfatide, the level of sulfatide and the specific activity of the enzyme 3'-phosphoadenosine 5'-phosphosulfate:galactosylceramide sulfotransferase in the cells increased three- to fourfold. The level of cerebroside and the specific activity of UDP-galactose:hydroxyacyl sphingosine galactosyltransferase also increased threefold in the cells on treatment with cortisol. The effect of the hormone on the synthesis of cerebroside preceded the increase in sulfatide synthesis. Experiments with cycloheximide and actinomycin D showed that the effect of the hormone on glycolipid synthesis in these cells were mediated through de novo messenger RNA and protein synthesis. Removal of serum from the culture medium resulted in an approximately twofold enhancement of H235SO4 incorporation into sulfatide within 24 h. The levels of sulfatide and cerebroside and the specific activity of the galactosyltransferase and sulfotransferase also increased significantly after serum removal. However, in contrast to the effect of the steroid, the sulfotransferase activity and the level of sulfatide increased prior to elevations in galactosyltransferase and cerebroside. The effect of serum removal was also found to be mediated by de novo RNA and protein synthesis. The effects of cortisol and serum removal on the synthesis of cerebroside and sulfatide were strictly additive.

Neonatal malnutrition in the rat affects the delivery of sulfatides from microsomes and their entry into myelin

Brain slices from 18 day old normal and malnourished rats were incubated in the presence of [35S]sulfate to explore its incorporation into sulfatides of a total brain homogenate and the appearance of labeled sulfatides in different subcellular fractions. While the incorporation of label into sulfatides of the total homogenate was similar in both groups of animals, in subcellular fractions separated on a linear sucrose density gradient, labeling of sulfatides in malnourished animals was relatively higher in the region corresponding to the microsomal fraction. Time course incorporation and pulse-chase experiments were carried out to explore the kinetics of labeling of microsomal and myelin sulfatides. In pulse-chase experiments, normal controls showed a decrease in the specific radioactivity of sulfatides in the microsomal fraction after the chase, which was not observed in malnourished animals, while the appearance of labeled sulfatides in the myelin fraction of the latter group of animals was found to be lower than in normals. These results suggest that in neonatal malnutrition there is a defect in the transport of de novo synthesized sulfatides towards myelin or/and a problem in the assembly of these lipids into the myelin membrane.

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)

Synthesis and subcellular transport of sulfogalactosyl glycerolipids in the myelinating mouse brain

In the 17-day-old myelinating mouse brain the site of sulfogalactosyl glycerolipid synthesis and the kinetics of its subcellular distribution were studied by a 2 h pulse-labeling with [35S]sulfate followed by a 4 h chase of [35S]sulfogalactosyl glycerolipid. At several time intervals after the intraperitoneal [35S]sulfate injection, subcellular fractions of brain were obtained by differential and discontinuous sucrose gradient centrifugation. The crude microsomal membrane fraction (17 500 X g supernatant) was further subfractionated into light myelin, plasma membranes, Golgi vesicles, endoplasmic reticulum membranes and heavy vesicles associated with acid hydrolase activities. The results of the [35S]sulfogalactosyl glycerolipid labeling kinetics indicate that these lipids are synthesized in the Golgi-endoplasmic reticulum complex and transferred in vesicles associated with lysosomes to the myelin membranes. During this transfer part of the sulfogalactosyl glycerolipids appears to be degraded, similarly as described for brain sulfatides. This double function of lysosomes may be part of a general regulation mechanism of brain myelin glycolipid content.

Increased deposition of cholesterol in brain after electroconvulsive seizure

Rats injected intracranially with cholesterol precursors and subjected to electroconvulsive seizures showed significantly higher levels of deposition of [4-14C]cholesterol into brain cholesterol than controls. The degree of incorporation was cholesterol greater than mevalonic acid greater than sodium acetate; in each case convulsed animals exceeded unshocked animals. Enhanced turnover of brain cholesterol with incorporation of circulating sterol may be associated with the etiology of convulsive seizures.

Distribution of lipid synthesizing enzymes, 2',3'-cyclic nucleotide 3'-phosphodiesterase, and myelin proteins in rat forebrain subfractions during development

The distribution of UDP-galactose:ceramide galactosyltransferase (CGalT) was studied in subcellular fractions of rat forebrain during development using zonal centrifugation on linear gradients. Specialized subfractions: SN 1, a microsomal fraction, SN 4, a myelin-related fraction, and purified myelin were also used for this study. For comparison, two microsomal lipid synthesizing enzymes, a myelin-specific enzyme, 2',3'-cyclic nucleotide 3'-phosphodiesterase and myelin proteins were measured in the same subfractions. UDP-glucose:ceramide glucosyltransferase and cerebroside sulfotransferase were confined to microsomes. CGalT was localized in microsomes, but also in myelin and myelin-related fractions. The developmental change in distribution of CGalT in adult animals toward myelin containing fractions could indicate that the replacement of galactosylceramide in compact myelin could be carried out in close proximity to compact myelin (mesaxon, paranodal loops) rather than in the distant oligodendrocyte perikaryon.

Turnover rate of molecular species of sphingomyelin in rat brain

Turnover rate of individual molecular species of sphingomyelin of adult rat brain myelin and microsomal membranes was determined after an intracerebral injection of 100 microCi of [C3H3]choline. Myelin and microsomal membrane sphingomyelins were isolated from the rest of the lipids. The individual molecular species of benzoylated sphingomyelin were separated and quantitated by reversed-phase high performance liquid chromatography. All individual major molecular species of microsomal and myelin sphingomyelin had maximum incorporation at 6 and 15 days, respectively, after the injection. The specific radioactivity of all the various molecular species of both myelin and microsomal sphingomyelin declined at a similar rate after reaching a maximum. There was no significant difference in the turnover rate of short chain (16:0, 18:0) and long chain (greater than 22:0) fatty acid containing sphingomyelin. The average apparent turnover rate of myelin and microsomal sphingomyelin molecular species was about 14-16 days for the fast pool and about 45 days for the slow pool. It is concluded that individual molecular species of sphingomyelin of myelin and microsomal membranes turned over at a similar rate. Thus, turnover rate of sphingomyelin in myelin and microsomal membranes is not affected by the fatty acyl composition of the lipid.

Net sulfatide synthesis, galactosylceramide sulfotransferase and arylsulfatase A activity in the developing cerebrum and cerebellum of normal mice and myelin-deficient jimpy mice

Net sulfatide synthesis, galactosylceramide sulfotransferase (EC 2.8.2.11) and arylsulfatase A (EC 3.1.6.1) activities were measured in two brain regions, cerebrum and cerebellum, of normal and jimpy mice during postnatal development. In normally myelinating mice, two phases of increasing rates of net sulfatide synthesis were observed, the first coinciding with oligodendrocyte proliferation and the second with myelination. Net sulfatide synthesis was quantitatively higher in the cerebellum than in the cerebrum. In both brain regions, the developmental patterns of net sulfatide synthesis were related to the activity patterns of both galactosylceramide sulfotransferase and arylsulfatase A. In jimpy mice, a neurological mutant showing hypomyelination in brain, the first phase of net sulfatide synthesis was preserved in both brain regions and galactosylceramide sulfotransferase and arylsulfatase A activities were normal up to 12 days. However, during the phase in which myelination occurred in controls, the net sulfatide synthesis in both brain regions of jimpy mice was zero or even negative. The sulfatide deficit was larger in the cerebellum than in the cerebrum. In both mutant brain parts, galactosylceramide sulfotransferase activity increased up to 12 days showing about 50% of the maximal activities observed in normal brain regions. Thereafter up to 15 days, enzyme activity decreased to about 25% of that of controls and remained low in both brain regions. The developmental patterns and the activities of arylsulfatase A were, however, normal in the cerebrum and cerebellum of jimpy mice. These results suggest that the enzyme activities and the developmental patterns of galactosylceramide sulfotransferase and arylsulfatase A as measured in vitro reflect to a high degree their functional activity in vivo. Furthermore, sulfatide degradation by arylsulfatase A seems to be important in regulating net sulfatide synthesis during normal and impaired myelination.

Synthesis of lipids in mouse brain cell cultures during development

Several metabolic activities in dissociated cultures of newborn mouse brain were compared to the situation in vivo. The developmental activity pattern of cerebroside-sulfotransferase, cyclic nucleotide phosphohydrolase, and beta-hydroxy-beta-methyl glutaryl-coenzyme A-reductase and the synthesis and deposition of sulfatide and cholesterol in culture were estimated. The enzyme activity patterns in vivo and in culture are the same. Since the cultures show very little myelin formation, the parallel increase of enzyme activities necessary for myelination in vivo and in culture suggest the existence of intrinsic factors regulating the biochemical differentiation. In addition, the formation of the products, determined in culture, follows the patterns of the enzyme activities. Dissociated brain cell cultures are therefore a valid model for the study of biochemical parameters related to the synthesis of brain lipids during development.

3'-phosphoadenylylsulfate:galactosylceramide 3'-sulfotransferase. An optimized assay in homogenates of developing brain

An optimized in vitro assay of 3'-phosphoadenylysulfate:galactosylceramide 3'-sulfotransferase (EC 2.8.2.11, galactosylceramide sulfotransferase, formerly known as galactocerebroside sulfotransferase) activity is presented, that can be used in crude homogenate of brain tissue of various developmental stages. The enzyme activity is determined by measuring the [35S]sulfatides formed by the enzymic transfer of [35S]sulfate from 3'-phosphoadenoside 5'-phospho [35S]sulfate to galactosylceramides. The sulfatide formation at 30 degrees C is linear up to 30 min and up to a protein concentration of 1 mg per 0.5 ml assay volume. The presence of 0.4% Triton X-100 and 50 micrometer exogenous bovine cerebrosides are optimal for enzyme activity. The pH optimum of the reaction is at pH 6.5 using 0.1 M imidazole buffer. The enzyme reaction is stimulated by NaCl, KCl, MgCl2, CaCl2, MnCl2, ATP and inhibited by ADP. The developmental enzyme activity pattern of mouse brain is the same, if derived from homogenates and microsomes, respectively, under our assay conditions.

Biochemical changes in the central nervous system with age in the rat

Studies dealing with biochemistry of the central nervous system of rats have been reviewed. Data on the effects of age on enzyme activity and cellular substrates have been summarized in tabular form. In general, it can be concluded that biochemical functions dealing with anabolism decrease whereas those dealing with catabolism increase as aging progresses.

Incorporation of inorganic sulfate in rat-liver Golgi

Partial subcellular distribution and specifically the incorporation of 35SO4 in the Golgi apparatus of rat liver was studied. The isolated Golgi fraction was placed on a further sucrose gradient for subfraction and in all samples the total incorporated label, the trichloroacetic-acid-soluble and insoluble, and chloroform/methanol-soluble and insoluble amounts of label were measured. Approximately 2.3% of the total injected 35S was found in the liver, of which 2% was localized in the isolated Golgi fraction. Further subfractionation of the Golgi has shown that the majority of the 35S is localized at densities 1.12-1.13 g/cm3 in the gradient. In the isolated Golgi fraction 85% of the label was present in the trichloroacetic-acid-soluble and 15% in the insoluble part. Approximately 1% of the label in the Golgi fraction was soluble in chloroform/methanol. On the bases of radioactivity per weight of protein and total radioactivity, the Golgi fractions had the highest activity, except the first supernatant which had higher radioactivity. Briefly, a significant amount of the 35SO4 can be found in the isolated rat liver Golgi 15 min after the injection of the label, and the majority of this label is localized in the material sedimenting at density 1.12-1.13 g/cm3 after subfractionation of the Golgi apparatus.