Distribution of PNS myelin proteins and membrane enzymes in fractions isolated by continuous gradient zonal centrifugation

Isolation of myelin

The methods used to prepare myelin involve homogenization of the tissue in isotonic sucrose solution, followed by the isolation of myelin membranes by a series of steps that include density gradient centrifugation and differential centrifugation. Homogenization of nervous tissue in isotonic sucrose causes the myelin sheath to peel from the axon and form relatively large myelin vesicles. The large size of the myelin vesicles, together with the fact that myelin membrane has a lower density than other biological membranes, make differential centrifugation and density gradient centrifugation the main tools for the isolation of this membrane. Three protocols are outlined in this unit: isolation of a highly-purified myelin fraction from the central nervous system (CNS); separation of a highly-purified CNS myelin fraction into subfractions of different densities; and isolation of myelin from the peripheral nervous system (PNS).

Cyclosporin A: effects on the secretory process and noradrenergic activity in the submandibular gland of the rat

OBJECTIVES

The aim of the present work was to study the effect of long-term cyclosporine (CSA) administration on norepinephrine (NE) metabolism and adrenergic-evoked secretion in the rat submandibular gland (SMG).

METHODS

Dose-response curves to adrenergic agonists (methoxamine, isoproterenol, NE) were performed in control and CSA (10 and 30 mg/kg every 2 days for 1 month)-treated rats after SMG duct cannulation. In SMG tissue neuronal NE uptake, release, synthesis and endogenous content were determined. In addition phosphoinositide intracellular signaling was also investigated.

RESULTS

CSA administration caused an increase in salivary secretion evoked by methoxamine (alpha-adrenergic agonist) and NE but failed to modify salivation evoked by beta-adrenergic stimulation (isoproterenol). Long-term CSA administration decreased NE release and synthesis whereas it enhanced the amine uptake and phosphoinositide hydrolysis in the SMG.

CONCLUSIONS

The administration of CSA for 30 days induced salivary gland sensitization likely mediated by diminished adrenergic input. Present results suggest that the decreased sympathetic activity evoked by long-term CSA administration in the rat SMG may lead to sensitization of the gland supported by increased phosphoinositide hydrolysis and enhanced adrenergic-evoked salivation.

Alterations in gene expression associated with primary demyelination and remyelination in the peripheral nervous system

Primary demyelination is an important component of a number of human diseases and toxic neuropathies. Animal models of primary demyelination are useful for isolating processes involved in myelin breakdown and remyelination because the complicating events associated with axonal degeneration and regeneration are not present. The tellurium neuropathy model has proven especially useful in this respect. Tellurium specifically blocks synthesis of cholesterol, a major component of PNS myelin. The resulting cholesterol deficit in myelin-producing Schwann cells rapidly leads to sychronous primary demyelination of the sciatic nerve, which is followed by rapid synchronous remyelination when tellurium exposure is discontinued. Known alterations in gene expression for myelin proteins and for other proteins involved in the sequence of events associated with demyelination and subsequent remyelination in the PNS are reviewed, and new data regarding gene expression changes during tellurium neuropathy are presented and discussed.

The antibody repertoire in experimental allergic neuritis: evidence for PMP-22 as a novel neuritogen

Experimental allergic neuritis (EAN) is an autoimmune disease that serves as an animal model for the Guillain-Barré syndrome (GBS). In both disorders there is still great uncertainty as to the significance and diversity of autoantibodies involved. We focused on the characterization of serum antibody production in response to various peripheral nervous system (PNS) myelin proteins during the course of actively induced EAN in Lewis rats. These data were compared with EAN induced by adoptive transfer of P2-specific CD4+ T cells (AT-EAN) and with inoculation with complete Freund's adjuvant (CFA) alone. Semiquantitative Western blotting was applied to measure serum IgM and IgG titers against specific myelin proteins, including P2, P0, myelin basic protein (MBP), myelin-associated glycoprotein (MAG) and PMP-22. Considerable differences in the dynamics of antibody titers against individual myelin proteins were observed in active EAN and after inoculation with CFA alone. Our data suggest a pathogenic role of IgM antibodies against HNK adhesion carbohydrate epitope expressing PNS proteins P0, MAG and PMP-22. Among these, PMP-22, a novel candidate neuritogen may be of particular relevance. Thus, we provide evidence for the involvement of antibody-mediated immune response in actively induced EAN and a basis for similar studies on related human disorders such as GBS or other demyelinating neuropathies.

Isolation and characterization of axolemma-enriched fractions from rabbit and bovine peripheral nerve

Axolemma-enriched fractions were isolated from bovine spinal accessory nerves, bovine intradural dorsal roots, and rabbit sciatic nerve by differential centrifugation and separation on a linear 10-40% sucrose (w/w) gradient. The fractions were enriched 4 to 10 fold in acetylcholinesterase, a biochemical marker for axolemma. Axolemma-enriched fractions isolated from uniformly well-myelinated fibers (bovine spinal accessory nerve) contained lower CNPase activity and higher acetylcholinesterase activity than comparable fractions isolated from variably myelinated fibers (rabbit sciatic nerve and bovine intradural roots). Separation by polyacrylamide electrophoresis showed that the molecular weight distribution of all peripheral nerve axolemma-enriched fractions was similar and ranged from 20 to over 150 kilodaltons. All axolemma-enriched fractions appeared to contain a small but variable amount of myelin-specific proteins. Based on biochemical properties, peripheral nerves containing uniformly well-myelinated fibers yield an axolemma-enriched fraction which is least contaminated with myelin-related membranes.

Primary demyelination induced by exposure to tellurium alters mRNA levels for nerve growth factor receptor, SCIP, 2',3'-cyclic nucleotide 3'-phosphodiesterase, and myelin proteolipid protein in rat sciatic nerve

Weanling rats fed a diet containing tellurium develop a peripheral neuropathy characterized by a highly synchronous primary demyelination; this demyelination is followed closely by a period of rapid remyelination. The demyelination is related to the inhibition of squalene epoxidase activity, which results in a block in cholesterol synthesis. Expression of mRNA for the major structural proteins of PNS myelin, myelin basic protein and P0, is coordinately down-regulated during the demyelinating phase and then up-regulated during the remyelinating phase (Toews et al., J. Neurosci. Res., 26 (1990) 501-507). We now report tellurium-induced alterations in gene expression for several proteins which are not major structural components of myelin in the peripheral nervous system. Expression of mRNA for nerve growth factor receptor in sciatic nerve was very low in control animals, but was markedly up-regulated after 3-5 days of exposure to tellurium, a time corresponding to the beginning of demyelination. Levels remained elevated during the subsequent period of remyelination. Expression of mRNA for SCIP (a presumptive transcription factor) was also up-regulated in sciatic nerve following tellurium exposure, with a time course similar to that for nerve growth factor receptor. When examined as a fraction of total RNA, steady-state mRNA levels for 2',3'-cyclic nucleotide 3'-phosphodiesterase and the myelin proteolipid protein were decreased during the demyelinating phase; however, this decrease could be largely accounted for by increased levels of total RNA. When analyzed on a 'per nerve' basis, steady-state mRNA levels for these two proteins were actually increased about 2-fold by 9 days after beginning tellurium exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteolysis of peripheral nerve myelin in acute experimental allergic neuritis

Proteolysis of peripheral nerve myelin was studied in rats with experimental allergic neuritis (EAN). In vitro measurements using rat sciatic nerve homogenate and denatured bovine myelin as a substrate showed two myelin specific enzyme activities at pH 3.8 (inhibited by pepstatin) and pH 5.8 (inhibited by PMSF) in the normal rat and newly appearing activities at pH 2.8 (inhibited by pepstatin) and pH 5.0 (not characterized) in the EAN rat. In EAN the proteolytic activity was not restricted to myelin substrate but degraded total sciatic nerve protein as well. Endogenous sciatic nerve protease at pH 5.8 did not significantly change in activity during the course of disease. On the contrary, activity of acid protease at pH 2.8 corresponded well to the disease. Myelin degradation in EAN, therefore, appears to be mainly due to exogenous non-tissue protease.

Quantitative analysis of myelin protein gene expression during development in the rat sciatic nerve

We determined the temporal profile of expression of the genes encoding the P0 glycoprotein, the myelin-associated glycoprotein (MAG), the myelin basic protein (MBP), the proteolipid protein (PLP), and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) in the sciatic nerve of rats. The level of expression of the MAG gene occurred maximally in animals 13 days of age, approximately one week earlier than the peak expression of the MBP and P0 genes. The genes encoding PLP and CNP were not expressed developmentally in a manner that correlated with the myelination of the sciatic nerve. Furthermore, using RNA synthesized in vitro, specific for each of the myelin protein genes, we have determined the absolute amounts of messenger RNA for the various myelin proteins in total RNA from sciatic nerves. P0 and MBP RNA were present at very high levels, whereas the amount of MAG, PLP and CNP RNA were much less.

Prednisolone therapy of experimental allergic neuritis in Lewis rats does not induce relapsing or chronic disease

The effects of therapeutic prednisolone treatment on experimental allergic neuritis (EAN) in Lewis rats were evaluated in a controlled clinical and electrophysiological study. Since steroid therapy has been suspected to cause relapsing or chronic disease, monitoring was extended over 200 days. Short-term steroid treatment (5 days of 15 mg/kg prednisolone, n = 8) with sudden steroid withdrawal was compared with long-term application (30 days, beginning at 7.5 mg/kg) in descending dosage (n = 8). The experiment included saline-injected controls (n = 8) and controls for stress possibly exerted by the handling of the animals. Treatment was begun at the onset of clinical signs. The clinical and electrophysiological data indicated that deterioration, recovery and mild (insignificant) relapse (after day 30 and day 108) occurred in all groups at the same time. Both steroid application schemes significantly (p less than 0.03) attenuated the severity and shortened the duration of EAN. Relapse was not aggravated after steroid treatment. The clinical course and electrophysiological findings were unaltered by the experimental procedures and by mild experimental stress.

Relationship of ATP turnover, polyphosphoinositide metabolism, and protein phosphorylation in sciatic nerve and derived peripheral myelin subfractions from normal and streptozotocin diabetic rats

Sciatic nerve from streptozotocin-induced diabetic rats has previously been shown to incorporate more 32P into phosphatidylinositol-4,5-bisphosphate (PIP2) and the principal myelin proteins than normal nerve. In the present study, labeling of ATP and PIP2 was compared. Using nerve segments, [gamma-32P]ATP specific activity reached a plateau after incubation for 4 h with [32P]orthophosphate, whereas the specific activity of [32P]PIP2 rose much more slowly and was still increasing after 8 h. The rate of disappearance of radioactivity from prelabeled ATP was biphasic, with 75% being lost within 30 min and the remainder declining much more slowly for several hours thereafter. In contrast, no decrease in prelabeled PIP2 radioactivity could be detected for up to 4 h. The kinetics of ATP metabolism were not appreciably different for normal and diabetic nerve. However, after incubation with [32P]orthophosphate for 2 h, the specific activity of PIP2 was 50-120% higher in diabetic nerve. This phenomenon, therefore, cannot be ascribed to altered specific activity of the ATP precursor pool. Greater labeling of PIP2 in 32P-labeled diabetic nerve was present in purified myelin isolated using a simple discontinuous sucrose density gradient, but not in a "nonmyelin" fraction. When nerve homogenate was fractionated on a more complex gradient, three myelin-enriched subfractions were obtained which were heterogeneous as judged by morphological appearance, protein profile, and lipid metabolic activity. The proportion of total lipid radioactivity accounted for by PIP2 was elevated in all the subfractions relative to the homogenate. As compared to myelin subfractions from normal nerve, an increased percentage of 32P in PIP2 was obtained only in the major myelin subfraction from diabetic nerve. The phosphorylation of P0 relative to the other myelin proteins was also enhanced in this subfraction in nerve from diabetic animals.

Demyelination of sciatic nerve in acute experimental allergic neuritis of the rat. A gel electrophoresis investigation

Acute experimental allergic neuritis (EAN) of Lewis rats was monitored by clinical and electrophysiological tests for 60 days. Sciatic nerve myelin proteins were analyzed by quantitative microgel electrophoresis and electroimmunoblotting at different clinical stages of the disease. The clinical severity of EAN and the demyelination as measured by electrophysiological tests and myelin protein concentrations in sciatic nerve did not correspond during the course of the disease. Demyelination reached its peak after partial clinical recovery and was still present on day 60. The major peripheral nervous system (PNS) myelin proteins P0, P1 and P2 decreased at different rates during the course of the disease, indicating possible differences in their proteolytic degradation. Treatment with Freund's complete adjuvant (CFA) alone resulted in alterations of membrane and myelin protein patterns challenging the widely held belief that pure CFA is inert with regard to demyelination.

Membrane interactions in nerve myelin: II. Determination of surface charge from biochemical data

In our accompanying paper (Inouye and Kirschner, 1988) we calculated the surface charge density at the extracellular surfaces in peripheral and central nervous system (PNS; CNS) myelins from observations on the dependency of the width of the extracellular space on pH and ionic strength. Here, we have determined the surface charge density of the membrane surfaces in myelin from its chemical composition and the localization of some of its molecular components. We then analyzed the attractive and repulsive forces between the apposed surfaces and calculated equilibrium periods for comparison with the measured values. The biochemical model accounts for the observed isoelectric range of the myelin period and, with the surface charge reduced (possibly by divalent cation binding or a space charge approximation), the model also accounts for the dependency of period on pH above the isoelectric range. At the extracellular (and cytoplasmic) surfaces the contribution of lipid (with pI approximately 2) to the net surface charge is about the same in both PNS and CNS myelin, whereas the contribution of protein depends on which ones are exposed at the two surfaces. The protein conformation and localization modulate the surface charge of the lipid, resulting in positively-charged cytoplasmic surfaces (pI approximately 9) and negatively-charged extracellular surfaces (pI approximately 2-4). The net negative charge at the extracellular surface is due in CNS myelin to lipid, and in PNS myelin to both lipid and (PO) glycoprotein. The net positive charge at the cytoplasmic surface is due in CNS myelin mostly to basic protein, and in PNS myelin to PO glycoprotein and basic protein. The invariance of the cytoplasmic packing may be due to specific short-range interactions. Our models demonstrate how the particular myelin proteins and their localization and conformation can account for the differences in inter-membrane interactions in CNS and PNS myelins.

Isolation of myelinoid Marchi-positive bodies from normal rabbit spinal cord

Normal rabbit spinal cord was homogenized in sucrose and fractionated by centrifugation in a sucrose density gradient system slightly modified after the Norton-Poduslo method for the isolation of myelin. The following fractions were recovered: the fraction floating on 0.32 M sucrose, the myelin fraction at the 0.32 M/0.85 M interface and the pellet. After fixation in glutaraldehyde the fractions were subjected to Marchi staining, a histochemical method used for the demonstration of degenerating myelin. The floating fraction was enriched in Marchi-positive bodies as compared to the homogenate while the myelin fraction and the pellet contained low amounts. No esterified cholesterol was found in the floating fraction. Since histochemical and electron microscopical studies have shown that Marchi-positive myelinoid bodies in the normal CNS are associated with node-paranode regions our results indicate a possibility to isolate and biochemically characterize a presumably closely myelin-related fraction of known anatomical origin. The absence of esterified cholesterol in the floating fraction shows that biochemical or biophysical properties other than a content of esterified cholesterol may give rise to a positive Marchi reaction.

Subcellular fractionation of rat sciatic nerve and specific localization of ganglioside LM1 in rat nerve myelin

Subcellular fractionation of rat sciatic nerve was developed to determine the specific localization of gangliosides in the nerve membrane fractions. Myelin, microsomal, and a plasma membrane-like fraction were isolated and purified by sucrose density gradient centrifugation. These subfractions were characterized by electron microscopy, marker enzyme assays, and their protein and lipid profile. In rat sciatic nerve myelin, 90 mol% of the total gangliosides were monosialogangliosides. LM1 (sialosyl-lactoneotetraosylceramide) (61 mol%) and GM3 (21%) were the major gangliosides of the rat nerve myelin. Two other neolacto series of gangliosides, viz., sialosyl-lactoneonorhexaosylceramide and sialosyl-lactoneooctaosylceramide, were also localized mostly in the myelin fraction. GM1 was only a minor (less than 2%) ganglioside in myelin. The ganglioside patterns of the microsomal and plasma membrane-like fractions were similar with minor quantitative differences and were entirely different from that of myelin. Monosialogangliosides were approximately 70-75 mol% of the total in these fractions. The major gangliosides of the microsomal and plasma membrane-like fractions were GM3 (approximately 40%) and GM1 (approximately 20%). LM1 in these fractions was minimal (less than approximately 5%). Significant amounts of GM3 with N-glycolylneuraminic acid (approximately 10%) and GM1b (4-14%) were also identified in the microsomal and plasma membrane-like fractions but not in myelin. These and the higher lactoneo series of gangliosides have not been previously reported to be present in the rat nervous system. Almost exclusive localization of LM1 in myelin in rat peripheral nervous system is consistent with our previous observation that deposition of LM1 in the nerve with age was very similar to that of myelin marker lipids cerebrosides and sulfatides.

Activity of 2'3'-cyclic-nucleotide 3'-phosphodiesterase and content of PO protein in the peripheral nervous system of the dystrophic mouse and chicken

To investigate whether various myelin markers could detect pathological changes in myelination, the activity of 2'-3'-cyclic nucleotide 3'-phosphodiesterase (CNP) and the level of PO protein were compared in the peripheral nervous system (PNS) of the dystrophic mouse and chicken and their phenotypically normal siblings. The same comparison was made for subcellular fractions of these nerves. The level of PO protein and the activity of CNP were normal in the spinal roots of sciatic nerves of the 129B6F1/Jdy/dy strain of dystrophic mouse. These parameters were slightly but significantly lower in the spinal roots of the 129REJ/dy/dy strain of dystrophic mouse. These results suggest that the 129B6F1/Jdy/dy mutant and the 129REJ/dy/dy mutant mouse might not have the same type of biochemical abnormality in their PNS. The specific activity of CNP and the proportion of PO protein increased significantly in the various regions of the PNS of 1-day-old chicks when compared to that of the 18-day-old embryos. Subcellular fractionation of peripheral nerves indicated that these components were enriched in the crude myelin fraction. These results support the conclusion that PO protein and CNP are suitable markers of myelinogenesis in the PNS of the chick. These parameters were normal in the line 413 dystrophic chicken. These results do not support the conclusion of a systemic membrane defect in the PNS of the dystrophic mouse and chicken.

PO protein and 2',3'-cyclic-nucleotide 3'-phosphodiesterase activity in the peripheral nerve and subcellular fractions of the Trembler mouse

To investigate the biochemical abnormalities of the Trembler mouse, the level of the PO protein (as % of total protein) and the activity of CNP was compared in the sciatic nerve and subcellular fractions of normal and mutant littermates. There was a significant decrease in both of these myelin markers in total nerve homgenates of the neurological mutant compared with the control animals. Immunoassay of the PO protein and polyacrylamide gel analysis of proteins indicated an accumulation of a protein with an apparent molecular weight of 67K in mutant nerve extracts. The mutant nerve also had relatively decreased levels of a protein of molecular weight about 41K that cross-reacted with antibody to PO protein. The Trembler mouse exhibited a larger percentage recovery of PO protein and CNP activity in subcellular fractions denser than the myelin sheath. Together these results are consistent with the theories that these denser components represent immature forms of myelin and that the Trembler mutant is characterized by hypomyelination.

Identification of an axolemma-enriched fraction from peripheral nerve

A method has been devised for the fractionation of whole peripheral nerve. The procedure utilizes differential centrifugation and separation on a linear sucrose gradient (10-40%, wt/wt). A membrane fraction localized between 26% and 29% sucrose was not only enriched for the plasma membrane markers, 5'-nucleotidase and acetylcholinesterase (AChE), but also possessed the highest binding of [3H]saxitoxin, a specific marker for sodium channels. Neurons in the lumbar dorsal roots and ventral horns of rats were injected with [3H]fucose to label glycoproteins associated with the axolemma from sciatic nerve. Fractionation of the labeled nerves demonstrated a coincidence in the distribution of [3H]fucose-labeled material and AChE activity in the sucrose density gradient. The increase in the specific activity of marker enzymes for plasma membrane, sodium channels, and labeled membrane, previously demonstrated to be of axolemmal origin, identified the 26-29% region of the sucrose gradient as enriched for axolemma derived from peripheral nerve.

Cholesterol esterifying enzyme in normal and degenerating peripheral nerve

The cholesterol esterifying enzyme which incorporates exogenous free [1-14C]oleate into cholesteryl ester is present in rat sciatic endoneurium. Cholesterol esterification is optimal at pH 4.8. Exogenous ATP, CoA, and oleyl-CoA do not greatly affect its activity. Various detergents and bile salts are inhibitory. Enzyme activity does not change appreciably during storage at 4 degrees C for up to 4 days or at -70 degrees C for up to 1 month. Of the subcellular fractions, the microsomal fraction exhibits the highest specific activity. Over 75% of enzyme activity is recovered, with equal amounts in the microsomal and soluble fractions. During nerve fiber degeneration an increase (more than fivefold) in cholesterol esterifying activity, which peaks 6 days after crush, is observed. Elevated levels of enzyme activity persist for 90 days after crush, by which time nerve regeneration is well established. Thus, it is concluded that an increase in cholesterol esterifying activity in degenerating nerve is primarily responsible for cholesterol esterification during Wallerian degeneration. The maximum increase in cholesterol esterifying activity is associated temporally with axonal degeneration and, particularly, with the formation of myelin ovoids.

The glycoprotein composition of peripheral nervous system myelin subfractions

Two fractions were isolated by continuous density gradient centrifugation from total particulate matter of rabbit sciatic nerves: a minor fraction, B, consisting of small-sized membrane fragments and a major fraction, C, of characteristic multilayered myelin figures, with maxima at 0.33 and 0.58 M-sucrose, respectively. In comparison with C, fraction B was enriched in CNPase and alkaline phosphatase activities and the P0, 23K and Z proteins, but was virtually devoid of basic protein. The glycoprotein composition of all fractions was examined with four fluorescein isothiocyanate-labelled lectins (WGA, Con A, RCA-60, U.E.). These revealed the presence of six glycoproteins in all fractions with similar lectin binding capacities and molecular weights ranging from 35,500 to 16,000, of which P0 was the predominant component. Material found on the heavy side of fraction C was characterized by the presence of a multitude of glycoproteins which bound variable proportions of the four different lectins, suggesting substantial variations in their carbohydrate moieties. Their absence from the central portion of fraction C points to a location other than that of compact PNS myelin.

The protein antigens of peripheral nerve myelin

Peripheral nervous system (PNS) tissue contains a variety of proteins, lipids, and carbohydrates that may serve as immunogens in proving immune responses, as antigens participating in immunological reactions, or as both types of agents. Three proteins P0, P1, and P2, account for approximately 70% of PNS myelin proteins. P0 is the major PNS myelin protein and is restricted to the PNS. P1 is similar to, if not identical with, myelin basic protein, the component of central nervous system myelin which induces experimental allergic encephalomyelitis. P2 has neuritogenic properties for inducing experimental allergic neuritis and may be involved in immune-mediated PNS myelin injury in humans. The complete amino acid sequence for P2 has recently been delineated, and its neuritogenic, immunogenic, and antigenic features can now be further characterized.

Evidence for the association of 2',3'-cyclic-nucleotide 3'-phosphodiesterase with myelin-related membranes in peripheral nervous system

In PNS, the specific activity of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) in myelin was not enriched over the starting homogenate. Nevertheless, most of the total activity was recovered in myelin. In myelin-deficient mutants, low CNP activities were measured in sciatic nerves. CNP specific activities were similar in myelinated and non-myelinated nerves but in non-nervous tissues, they were significantly lower than in nervous tissue. There was no indication for the presence of an isoenzyme of CNP in peripheral nerves. These results indicate that CNP is present in PNS myelin and preferentially localized in Schwann cell plasma membranes.

The lipid composition of light and heavy myelin subfractions isolated from rabbit sciatic nerve

Centrifugation of adult rabbit sciatic nerve homogenates on continuous sucrose density gradients yields three distinct maxima at 0.12, 0.33 and 0.57 M sucrose (labeled A, B and C), respectively. Fraction A is absent in homogenates of immature rabbit sciatic nerve and the material isolated from adult animals is found to contain large amounts of triglycerides. It is proposed that fraction A results from the presence of adipose tissue adhering to the adult nerve preparations and should not be regarded as a true myelin subfraction. The concentration of the major membrane lipid classes (phospholipid, cholesterol and galactosyl ceramide) decreases from the light to the heavy side of the gradient. The ethanolamine phosphatide to sphingomyelin ratio increases from 1.06 to 1.42 between fractions B and C, due to an increase in the phosphatidal ethanolamine content at the expense of sphingomyelin.

Studies on the Wolfgram high molecular weight CNS myelin proteins: relationship to 2',3'-cyclic nucleotide 3'-phosphodiesterase

Evidence is presented that the major protein components of the high molecular weight CNS myelin proteins designated as the Wolfgram protein doublet (W1 and W2) contain the enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37, CNP). CNP is a basic hydrophobic protein containing about 830 to 840 amino acid residues. When electrophoresed on SDS polyacrylamide gels, CNP appears as a protein doublet, separated by a molecular weight difference of about 2500-3000 in bovine, human, rat, guinea pig, and rabbit. A similar protein doublet has been identified as the Wolfgram proteins W2 and W1 in myelin and in the chloroform-methanol-insoluble pellet obtained from myelin. Moreover, the relative Coomassie blue staining intensity of the CNP2 plus CNP1 protein doublet among the species examined was remarkably similar to that observed for electrophoresed myelin and chloroform-methanol-insoluble pellet derived from myelin. Antisera raised against purified bovine CNP recognized the W1 and W2 proteins isolated from bovine and human brain. The amino acid composition of pure bovine CNP is presented and compared with the compositions of several rat and bovine Wolfgram proteins obtained by other investigators. Our electrophoretic, compositional, and immunological data support the contention that the enzyme CNP is a major component of the Wolfgram protein doublet.