Purification of myelin carbonic anhydrase

Purification and biochemical characterization of a novel carbonic anhydrase II from erythrocytes of camel (Camelusdromedarius)

A novel carbonic anhydrase II (CA II) from erythrocytes of camel (Camelus dromedarius) was purified to homogeneity using affinity chromatography and biochemically characterized. Specific activity of 140.88 U/mg was obtained with 745.17-fold purification and 25.37% yield. The enzyme was a monomer with a lower molecular weight (25 kDa) and lower Zn content (0.50 mol of Zn per mol of protein). The enzyme showed higher optimum temperature (70 °C) and pH (pH 9.0), moreover, it was stable at higher temperatures and strongly alkaline pH as judged by thermodynamic parameters (Ea, kd, Ed, t1/2, D-value, Z-value, ΔH, ΔG and ΔS). The enzyme was inhibited by cations (Al3+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Ni2+, Mg2+ and Zn2+) as well as by anions (Br‾, CH3COO‾, ClO4‾, CN‾, F‾, HCO3‾, I‾, N3‾, NO3‾ and SCN‾), some anions (C6H5O73-, CO32-, SeO3‾ and SO42-) does not affect enzyme activity. Effect of various chemicals on enzyme activity was also investigated. Km, Vmax, kcat and kcat/Km values for 4-NPA were found to be 1.74 mM, 0.0093 U/mL, 0,0039 s-1 and 0,0023 s-1 mM-1, respectively. With these interesting biochemical properties, camel CA II represents promising candidate for harsh industrial applications, in particular, for a successful biomimetic CO2 sequestration process.

Posthemorrhagic hydrocephalus and brain injury in the preterm infant: dilemmas in diagnosis and management

Advances in neonatal critical care have reduced the incidence of intraventricular hemorrhage (IVH) in the newborn. Paradoxically, however, the prevalence of the complications of IVH including posthemorrhagic hydrocephalus (PHHC) has increased. By virtue of its association with long-term neurodevelopmental disability, posthemorrhagic hydrocephalus is an ominous diagnosis in the premature infant. Animal models have demonstrated that ventricular distention may cause direct cerebral parenchymal injury. Evidence for secondary parenchymal injury in the premature infant with PHHC is by necessity indirect. The precise impact of secondary parenchymal injury on the overall neurological outcome of premature infants with PHHC remains unclear in large part because of the vulnerability of the immature brain to other forms of injury (e.g., periventricular leukomalacia) that may be difficult to distinguish from injury due to distention. Furthermore, parenchymal injury due to PVL may cause ventricular enlargement that does not benefit from CSF diversion. Because these primary and secondary mechanisms of injury may operate concurrently, the precise or dominant cause of ventricular enlargement is often difficult to establish with certainty in the neonatal period. These diagnostic dilemmas have in turn impeded the development and evaluation of therapies specifically aimed at reversing ventricular distention and preventing secondary parenchymal injury. This article focuses on the current dilemmas in diagnosis and management of this potentially reversible form of injury as well as on potential future strategies for its prevention.

Carbonic anhydrase II in microglia in forebrains of neonatal rats

In the brains of adult rodents carbonic anhydrase II (CA) immunoreactivity has been observed in the choroid plexus and in oligodendrocytes, astrocytes, and myelin. Localization and functions of CA in the neonatal brain, however, have been controversial. One issue is whether the CAII-immunopositive round and ameboid cells in the corpus callosum and cingulum in the rat CNS during the first postnatal week are oligodendrocytes or microglia. Colocalization of CAII with the microglial antigen, ED1, and the microglia-specific isolectin, BSI-B4, suggested that most (approx. 60%) of the CAII-positive round and ameboid cells in rat brain during the first postnatal week were, indeed, macrophages and microglia. During that initial week, some CAII-positive protoplasmic astrocytes (approx. 40%) were observed as well. At the end of the first postnatal week smooth-surfaced CAII-positive cells began to appear in the corpus callosum. Those cells also bound MAbO4, a marker for the oligodendrocyte cell line. We conclude that during the first postnatal week most of the CAII-positive cells are macrophages and microglia, and that some are protoplasmic astrocytes. During the second postnatal week CAII-positive cells in the oligodendrocyte lineage become apparent, and by the end of that week there are few CAII-positive microglia. Confocal microscopy suggests that in brains of three-day-old rats the ameboid microglia are associated with nerve fibers, where they may perform phagocytosis of axons, directional guidance of axons, or disinhibition of axonal growth.

Expression of carbonic anhydrase II mRNA and protein in oligodendrocytes during toxic demyelination in the young adult mouse

The aim of this study was to identify events that might take place in oligodendrocytes early in the process of demyelination, i.e., before the occurrence of massive loss of myelin. It was considered important to focus on demyelination and remyelination in young adults, in whose brains there would be relatively few juvenile glial precursor cells. CAII mRNA and protein were used to monitor changes in oligodendrocytes during cuprizone intoxication in the mice. After four or eight weeks of cuprizone feeding CAII message became less plentiful in oligodendrocyte processes. Two days after removal of cuprizone CAII message had appeared in those cell processes. Four or eight weeks after beginning cuprizone feeding CAII protein had decreased approximately 25% in forebrain homogenates. The loss of CAII protein was reversible after four weeks on cuprizone, but not after eight weeks. After four weeks of cuprizone feeding the numbers of CAII mRNA-positive oligodendrocytes had decreased by approximately 50%, and after eight weeks, by approximately 80%. By 12 weeks, however, the number of oligodendrocytes expressing CAII mRNA had spontaneously returned to normal levels. Before eight weeks of cuprizone feeding, loss of myelinated tracts in the corpus striatum was reversible. Demyelination appeared to become irreversible after nine weeks of intoxication, although expression of CAII mRNA remained reversible. The results suggest that in the brain of the young adult, oligodendrocytes expressing message for CAII can be generated spontaneously shortly before demyelination becomes irreversible, and can survive and continue to express CAII mRNA but not CAII protein.

Biochemical subtypes of oligodendrocyte in the anterior medullary velum of the rat as revealed by the monoclonal antibody Rip

Oligodendrocytes were studied in the anterior medullary velum (AMV) of the rat using the monoclonal antibody Rip, an oligodendrocyte marker of unknown function. Confocal microscopic imaging of double immunofluorescent labelling with antibodies to Rip and carbonic anhydrase II (CAII) revealed two biochemically and morphologically distinct populations of oligodendrocyte which were either Rip+CAII+ or Rip+CAII-. Double immunofluorescent labelling with Rip and myelin basic protein (MBP) or glial fibrillary acidic protein (GFAP) provided direct evidence that Rip-labelled cells were phenotypically oligodendrocytes and confirmed that Rip did not recognise astrocytes. Oligodendrocytes which were Rip+CAII+ supported numerous myelin sheaths for small diameter axons, whilst Rip+CAII- oligodendrocytes supported fewer myelin sheaths for large diameter axons. Morphologically, Rip+CAII+ oligodendrocytes corresponded to types I or II of classical nomenclature, whilst Rip+CAII- oligodendrocytes corresponded to types III and IV. The results demonstrated a biochemical difference between oligodendrocytes which myelinated small and large diameter fibres.

Familial periodic cerebellar ataxia: a problem of cerebellar intracellular pH homeostasis

Six affected members of two families with familial periodic cerebellar ataxia were relieved of their symptoms with oral acetazolamide. Phosphorus 31 (31P) nuclear magnetic resonance spectroscopy showed abnormal intracellular pH levels in the cerebellum of all subjects when they were not treated. These levels returned to normal with treatment. Cerebral pH values were also measured in one family and were normal before and after treatment. An additional 3 patients with similar attacks, but without a family history, had normal untreated pH values in the cerebellum and cerebrum.

Sarcolemmal carbonic anhydrase in red and white rabbit skeletal muscle

Sarcolemmal vesicles of white and red skeletal muscles of the rabbit were prepared by consecutive density gradient centrifugations in sucrose and dextran according to Seiler and Fleischer (1982, J. Biol. Chem. 257, 13,862-13,871). White and red muscle membrane fractions enriched in sarcolemma were characterized by high ouabain-sensitive Na+, K(+)-ATPase, by high Mg2(+)-ATPase activity, and by a high cholesterol content. Ca2(+)-ATPase activity, a marker enzyme for sarcoplasmic reticulum, was not detectable in the highly purified white and red muscle sarcolemmal fractions. White and red muscle sarcolemmal fractions exhibited no significant differences with regard to Na+, K(+)-ATPase, Mg2(+)-ATPase, and cholesterol. Specific activity of carbonic anhydrase in white muscle sarcolemmal fractions was 38 U.ml/mg and was 17.6 U.ml/mg in red muscle sarcolemma. Inhibition properties of sarcolemmal carbonic anhydrase were analyzed for acetazolamide, chlorzolamide, and cyanate. White muscle sarcolemmal carbonic anhydrase is characterized by inhibition constants, KI, toward acetazolamide of 4.6 X 10(-8) M, toward chlorzolamide of 0.75 X 10(-8) M, and toward cyanate of 1.3 X 10(-4) M. Red muscle sarcolemmal carbonic anhydrase is characterized by KI values toward acetazolamide of 8.1 X 10(-8) M, toward chlorzolamide of 6.3 X 10(-8) M, and toward cyanate of 0.81 X 10(-4) M. In contrast to the high specific carbonic anhydrase activities in sarcolemma, carbonic anhydrase activity in sarcoplasmic reticulum from white muscle varied between values of only 0.7 and 3.3 U.ml/mg. Carbonic anhydrase of red muscle sarcoplasmic reticulum ranged from 2.4 to 3.7 U.ml/mg.

Mechanisms of tolerance to the anticonvulsant effects of acetazolamide in mice: relation to the activity and amount of carbonic anhydrase in brain

The mechanism by which tolerance develops to the anticonvulsant effects of acetazolamide (AZM) was investigated in Swiss-Webster mice. The effects of single and six daily doses of 40 mg or 200 mg/kg AZM on electroshock seizure threshold (EST), maximal electroshock (MES) seizure pattern, and on the activity and total amount of carbonic anhydrase II (CAII) in various subcellular fractions (cytosol, microsomes, and myelin) of cerebral cortex, cerebellum, and brainstem were assessed. The activity of CAII was measured by microassay, and the total amount was measured by immunoassay methods developed in this laboratory. From the activity (units per microgram of protein) and total amount (nanograms per microgram protein) data, the specific activity (units per nanogram CAII) of the enzyme was calculated. With multiple doses, tolerance developed to both elevation of the EST and modification of the MES pattern noted with single doses of AZM. Accompanying the development of tolerance to the anticonvulsant effects of AZM was an increase in both the activity and specific activity of CAII in the various subcellular fractions and areas of the brain. The effects were dose dependent. Tolerance to the EST-elevating effects of AZM correlated with increases in the activity, total amount, and specific activity of CAII in the myelin fraction of the cerebral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbonic anhydrase activity develops postnatally in the rat optic nerve

We examined the appearance of carbonic anhydrase (CA) activity in rat optic nerves (RONs) 5-77 postnatal days of age and correlated the appearance of enzyme activity with structural and physiological alterations. CA activity was nearly absent before 10 days of age and appeared in this CNS white matter tract with a developmental time-course similar to that of oligodendrogliogenesis and myelinogenesis. When oligodendrocytes and myelin were depleted in the RON by treatment with a mitotic inhibitor, CA activity was markedly reduced. These observations support the hypothesis that CA is contained primarily in oligodendrocytes and myelin. Neural activity in the RON caused changes in extracellular pH (pHo) and the character of these pHo responses was very age dependent; older nerves exhibited much larger acid shifts than neonatal nerves. The development of CA activity may be a factor contributing to this physiological alteration.

Carbonic anhydrases

Some of the current studies of carbonic anhydrases are directed to the genetic mechanisms underlying their synthesis. Determination of the structure of their genes will probably most readily resolve the question of whether the membrane bound forms of the enzyme represent products of additional loci other than those of the three well-known soluble forms. Extensions of our knowledge of the sequences of these isozymes as well as those from lower animals and from plants will make possible a more precise evaluation of the extent of the multigene aspects of these proteins and their evolutionary backgrounds. Studies of the interrelationships of the regulation of the transcriptional and translational processes of the well-known isozymes and in particular the effects of hormones will be of interest. Insights into modifications of the isozymes' synthetic processes occurring in various diseases should also be forth-coming from these studies. In addition to the above the applications of what are perhaps today somewhat classical methods of protein chemistry will be needed to explore the reasons for the changes in activity accompanying the sequence variations of the different isozymes, the decreases or increases in activity accompanying derivatizations of specific residues and the reasons for the differences in the activity of different inhibitors on the various isozymes. The broad specificity of these enzymes for different substrates and the ability of CA-III to hydrolyze various phenyl esters and in some cases to become derivatized also present problems in protein structural chemistry. In terms of the latter reactions, the meaning of the relationships of these activities to those of the protein ubiquitin, which is homologous to CA-III, needs clarification. It would appear that various of the protein structural studies will be aided by crystallographic investigations of not only CA-III but of various of its derivatives which undergo either increases or decreases in activity. The above areas of studies present a wide variety of problems for workers in various disciplines and backgrounds who are interested in the carbonic anhydrases.

Histochemical study of the distribution of carbonic anhydrase in the cat brain

The distribution of carbonic anhydrase (CA) in cerebrum, cerebellum and medulla oblongata of the cat brain has been examined by a histochemical method. Neuron cell bodies and dendrites are stained in some locations. Many axons are distinctly stained and different intensities of staining can be seen even in adjacent axons. One of the most intensely stained structures is the capillary endothelium and stained capillaries are found in all parts examined. Glial cells are intensely stained in agreement with biochemical and earlier histochemical works. Myelin sheaths are never stained, possibly due to enzyme loss during embedding. The localization of the enzyme shows regional differences. In this respect, the medulla oblongata has been examined in more detail. A small area close to the ventral surface, medial to the roots of the hypoglossal nerve, is characterized by a high CA staining of the neuropil. The cell membrane of some large neurones and the capillary endothelium in this area were also stained. With regard to position and CA content, this area corresponds well to the characteristics of the medullary chemosensitive area as defined by previous experimental studies.

Resistance to disruption of multilamellar fragments of central nervous system myelin

Single-bilayer vesicles of myelin are desirable for studying myelin development and metabolism. Accordingly, our interest was drawn to a procedure for vesiculating myelin (Steck et al., Biochim, Biophys. Acta 509, 397-408, 1978). We used X-ray diffraction analysis to examine these putative vesicle preparations because much larger amounts of material can be surveyed by this method than by electron microscopy. The sharpness (width) of the rings in the X-ray diffraction pattern varies inversely with the number of bilayers per multilayer structure. We therefore expected to see the diffuse diffraction pattern characteristic of single bilayers. Diffraction patterns were recorded from isolated rat brain myelin before and after the vesiculation procedure. Both patterns showed sharp rings, indicating numerous multilayered structures. Average values ranging from 7 to 10 bilayers per multilayer were calculated in both cases. This procedure did produce a small fraction of single-bilayer structures, which were isolated by differential centrifugation; however, these accounted for only about 1% of the total myelin present. The diffraction pattern of this material showed the diffuse band typical of single-bilayer structures, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated it had the same protein composition as in normal myelin. Similar results were also obtained using either fresh or frozen bovine brain myelin. Variations of the published vesiculation procedure (incubation in 0.1 M NaCl or in buffers containing glycerol; disruption by sonication or use of a Tissumizer) also were not effective in breaking down the multilamellar fragments into thinner structures. The conclude that the multilamellar fragments of isolated CNS myelin resist disruption into single-bilayer structures.

Properties and function of brain carbonic anhydrase

This chapter has described the characterization and biogenesis of soluble and membrane-bound CA in the central nervous system. The two forms of the enzyme appear to be quite similar in their molecular characteristics, however the data strongly indicate that they are synthesized on separate polysomal populations; the membrane-bound form resulting from synthesis on the RER. Our preliminary data suggest that the partitioning of mRNA for CA on the different polysomes results from the interaction of partial nascent chains with a specific receptor on the RER. We feel a function of membrane-associated synthesis is for the targeting of CA to sites in the cell where there are enzymes that can rapidly utilize the protons and bicarbonate produced by CA catalytic activity for ion exchange reactions. We have also presented arguments that CA may function as a bicarbonate source in the control of metabolism specifically in the acceleration of fatty acid synthesis in the oligodendrocyte.

Characterization and biosynthesis of soluble and membrane-bound carbonic anhydrase in brain

Carbonic anhydrase from both the cytoplasmic and membrane fractions of the forebrains of rats was characterized with respect to enzymatic activity, immunoreactivity, and in vitro biosynthesis. A procedure for the rapid purification of both membrane-bound and soluble brain carbonic anhydrase is presented that permits retention of full enzymatic activity. Both forms of the enzyme were found to show specific activities of approximately 5500 Units/mg protein when CO2 hydrating activity was determined. In addition, they exhibited similar esterase activity when assayed with p-nitrophenyl acetate. The membrane-bound form, although requiring detergent for extraction from membranes, was freely soluble in aqueous buffers after purification. The molecular weights of both soluble and membrane-bound carbonic anhydrase are 30,000 daltons, and mixing experiments failed to show any significant differences with respect to size. The two forms also exhibit isoelectric points of 7.2. However, the two proteins were found to differ in two respects. Complement fixation indicated that antibodies to soluble carbonic anhydrase had a higher affinity for the soluble form than for the membrane-bound form. The failure to observe any precursor-product relationship between these two proteins with pulse chase studies and the establishment that carbonic anhydrase-like proteins are synthesized on both free polysomes and the rough endoplasmic reticulum indicated that these proteins are synthesized by two separate mechanisms. In vitro synthesis on both free and bound polysomes was determined by two independent methods using different antibodies and different analytical procedures. The basis for these findings and their physiologic importance are discussed.

Purification and properties of carbonic anhydrase from salmon erythrocytes

Carbonic anhydrase (CA) from erythrocytes of the pink salmon, Onchorhyncus gorbushka, was purified using chloroform-ethanol extraction and Sephadex G-75 gel filtration. A single, high specific-activity CA isozyme having a molecular weight of 29,000 was found. The enzyme sedimented as a single boundary at a sedimentation velocity of 2.9S. Amino acid analysis revealed a composition similar to other submammalian CAs with the exception that the cysteine content was low (1 mol cysteine/mol enzyme). Like other submammalian CAs, the presence of a sulfhydryl reducing agent was required to maintain full activity and to prevent structural changes in the enzyme.

Characterization of a high activity carbonic anhydrase isozyme purified from erythrocytes of Salmo gairdneri

1. A single, high specific activity carbonic anhydrase (CA) isozyme was present in erythrocytes of the teleostean species Salmo gairdneri (rainbow trout). 2. Purification of trout CA to homogeneity was accomplished using chloroform ethanol extraction, Sephadex G-75 gel filtration, and DEAE Bio-Gel anion exchange chromatography. 3. Trout CA was a zinc metalloenzyme of mol. wt 28,300 and pI9.3. 4. Amino acid analysis indicated the presence of 6 half-cystine residues per enzyme molecule, and the presence of a sulfhydryl reducing agent was required to maintain full activity in vitro. 5. Sulfhydryl modification with both N-ethylmaleimide and acrylonitrile indicated the presence of 3 reactive sulfhydryl groups per CA molecule. Modification of those groups had no direct effect on enzyme activity, but modified CA was no longer subject to inactivation by oxidizing conditions.

Lipoidal membranes stabilize isolated salmon and chicken carbonic anhydrase under conditions of increased temperature and pH

1. Solutions of purified carbonic anhydrase from chicken and salmon erythrocytes were incubated in buffer for 1 hr at 5 degrees or 22 degrees C, at pH 7.3, 7.6, 7.9 or 8.2. 2. At 22 degrees C the enzymes lost up to 25% of their ability to catalyze the CO2 hydration reaction when compared to control solutions maintained in the cold. 3. Loss of enzyme activity (approximately 50%) also occurred as pH was increased from 7.3 to 8.2. 4. The presence of lecithin vesicles or microsomes completely protected the enzymes from denaturation caused by pH changes and afforded partial protection from changes due to increased temperature.

Development of membrane-bound carbonic anhydrase and glial fibrillary acidic protein in normal and quaking mice

The developmental patterns of membrane-bound carbonic anhydrase (MBCA) and glial fibrillary acid protein (GFA) were analyzed in high speed pellets from subcortical regions of quaking and control mice at ages ranging from 10 to 42 days. In control, MBCA was found to increase from approximately 1.5 unit/mg protein at 10 days to about 11 units/mg protein at 42 days. The percent increase was greatest between days 11 and 18 where the activity increased 2.5-fold while the largest absolute weekly increment was in the fourth postnatal week. By contrast, the activity in quaking mice was 1.0 units/mg protein at day 10 and increased to only 5 units/mg protein by 42 days. The activity, although reduced at 10 days, appeared to increase in parallel with the controls between day 11 and 18; however, the large increment in activity observed in the controls during the fourth week was greatly reduced in the mutant. The above findings were also observed when immune reactive material was determined by immuno-blotting using antisera raised against MBCA isolated from brain. GFA was also estimated using an immuno-blotting procedure. In contrast to previous studies on soluble GFA, we found GFA to increase about 5-fold in the third postnatal week and level off thereafter. The Q/C ratio was 1.5 at 10 days, but, although GFA increased over 5-fold between 11 and 42 days, the absolute difference between quaking and control increased very little. These data on GFA and MBCA suggest that a defect in the expression of oligodendroglial plasma membrane proteins may be expressed early in development which may correlate with a small but significant gliosis and/or an increase in GFA synthesis.

Intraventricular hemorrhage in the premature infant

Periventricular-intraventricular hemorrhage is the most important adverse neurologic event of the newborn period. It is very common and can be very severe. Such hemorrhage begins in the germinal matrix but may spread into and throughout the ventricular system. It may be accompanied by hemorrhage within the brin parenchyma. The pathogenesis of periventricular-intraventricular hemorrhage is still imperfectly understood, but relates to the anatomy and physiology of the developing cerebral vasculature and to the biophysical and biochemical environment in which that development proceeds. Periventricular-intraventricular hemorrhage may be marked by a catastrophic clinical deterioration, but is more commonly accompanied by a saltatory progression that may be difficult to detect clinically. Both concomitant neonatal disease and therapeutic intervention for such disease have been implicated in the initiation and exacerbation of periventricular-intraventricular hemorrhage. Real-time ultrasound scanning with portable instruments is now the best procedure for identifying this lesion and for assessing its sequelae. Prognosis relates principally to the severity of the lesion. Early management must be particularly directed to the maintenance of cerebral perfusion. Later management is predominantly the therapy of posthemorrhagic hydrocephalus. There is no currently available therapeutic modality that will prevent progressive posthemorrhagic hydrocephalus.

Triethyl tin-induced myelin oedema: an intermediate swelling state detected by X-ray diffraction

X-ray diffraction was used to probe the effects of triethyl tin (TET) on the periodicity and amount of membrane disorientation in the lamellar myelin from respiring optic and sciatic nerves in vitro as well as from nerves of rats treated in vivo through their drinking water. The diffraction patterns show that in vitro TET at concentrations of 4-100 microM affects C.N.S. but not P.N.S. myelin structure. A planar, concentric membrane array with a 200 A period is detected in the C.N.S.; this ordered, swollen myelin contrasts with the vacuolar and vesicular structure seen in thin-sections in TET-induced oedema. No effects of short-term in vivo treatment with TET are observed in either the C.N.S. or P.N.S. The finding that carbonic anhydrase (CA) inhibitors have no effect on the TET-induced structural changes indicates that the swelling we observe is not related to a CA-dependent process. In comparison, the TET effect is prevented by replacing the mobile ions with isotonic sucrose. We conclude that TET-induced swelling in C.N.S. myelin arises from an increase in ion transport followed by obligatory fluid movement. Further, the ordered, swollen structure we detect may be an intermediate state that exists transiently in vivo in TET intoxication and that precedes the gross swelling and vacuolization usually observed.

Interactions of dicyclohexylcarbodiimide with myelin proteolipid

Dicyclohexylcarbodiimide (DCCD) is known to bind preferentially to a proteolipid subunit of proton-translocating systems and thereby to inhibit proton transport. In the present study we show that, in an aqueous medium, DCCD binds to the bovine white matter proteolipid apoprotein, the major protein of central nervous system myelin. The binding is dependent on time, temperature, and concentration and is not inhibited by the hydrophilic carbodiimide 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. By contrast, when the incubation is carried out in chloroform/methanol no labeling by DCCD is demonstrable. In isolated rat myelin, DCCD binds specifically to the proteolipid and not to the myelin basic proteins. Liposomes reconstituted with the myelin proteolipid apoprotein transport protons, as assayed by quenching of the fluorescence of 9-aminoacridine. Preincubation of proteolipid-containing liposomes with DCCD results in an inhibition of transport. These studies have important implications for a possible ionophoric function of the myelin proteolipid and for the occurrence of transport processes within myelin.

Seizures, hypoxic-ischemic brain injury, and intraventricular hemorrhage in the newborn

The review deals with neonatal seizures, perinatal hypoxic-ischemic brain injury, and neonatal intraventricular hemorrhage. neonatal seizures are the most prominent signals of the largest number of neonatal neurological disorders. The convulsive phenomena may be subtle. The predominant etiological process is hypoxic-ischemic encephalopathy. Prognosis is related primarily to the neurological disease responsible for the seizures. Treatment may be specific for the underlying disorder (e.g., glucose or calcium) or less specific (i.e., therapy with anticonvulsant drugs). Prompt control of the seizures is important to avoid brain injury secondary to the effects of the seizures on ventilation, perfusion, and brain metabolism. Hypoxic-ischemic encephalopathy in the newborn most often is a consequence of intrauterine asphyxia. Diagnosis depends primarily on recognition of the clinical syndrome but also on a variety of neurodiagnostic techniques, including radionuclide and CT brain scans. Prognosis is estimated best by a combination of clinical analysis and specialized neurodiagnostic studies. management is based principally on vigorous support, particularly of ventilation and perfusion, maintenance of adequate glucose influx, and control of seizures. Intraventricular hemorrhage is the most common type of neonatal intracranial hemorrhage. The neuropathology is characterized by bleeding from capillaries of the subependymal germinal matrix. Secondary rupture of the ependymal lining then causes intraventricular hemorrhage. Pathogenesis relates to the anatomy of the germinal matrix, the distribution and regulation of cerebral blood flow, and the structure and vulnerability of periventricular capillaries. Precise diagnosis requires a brain imaging procedure; portable, real-time ultrasound is the preferred approach for critically ill infants. Prognosis relates to the severity of the hemorrhage as well as any preceding hypoxic-ischemic insults and the subsequent occurrence of hydrocephalus. Choice of therapy for posthemorrhagic ventricular dilatation depends upon severity and rapidity of progression and ranges from close observation only to ventriculoperitoneal shunting.

Is Na + ATPase a myelin-associated enzyme?

The Na + K ATPase activity associated with purified myelin has been investigated. On the basis of marker enzyme studies, the Na + K ATPase activity of myelin was higher than could be accounted for by microsomal contamination. Fractions prepared from white matter-enriched areas of rat brain showed a threefold enrichment in Na + K ATPase activity in myelin as compared with the white matter homogenate. The ATPase activity in myelin was stimulated fourfold by treatment with sodium deoxycholate, but the activity in the whole brain homogenate and the microsomal fraction was only doubled. This discontinuity temperature for Na + K ATPase activity was significantly higher for the myelin fraction (29 degrees C) than for the microsomal fraction (21 degrees C), but the energies of activation, both above and below the discontinuity temperature, were the same for both fractions, Myelin Na + K ATPase had a lower affinity for strophanthidin than the microsomal enzyme, but both fractions were inhibited to the same extent by 10-3 M-strophanthidin. The evidence thus indicated that much of the ATPase activity of myelin is not the result of microsomal contamination. Although the possibility of axolemmal contamination cannot be ruled out conclusively, indirect evidence suggest that this is not a significant factor and that Na + K ATPase may be a myelin-associated enzyme.

Carbonic anhydrase distributions in central and peripheral nervous system of the rat

Total and specific carbonic anhydrase activity was measured for 24 structures of the rat central and peripheral nervous system. In the CNS, white matter or regions containing largely white matter show a neuraxial distribution of enzyme activity; more cephalad structures display more activity. Gray matter regions do not show a rostrocaudal distribution and usually have lower activity than adjacent myelin-containing structures. PNS tissue shows neither the white-gray differences nor the rostrocaudal profile of CNS tissue. Subcellular fractionation of 18 regions of the CNS suggest that the predominance of membrane-bound carbonic anhydrase (60% of the total activity and independent of its magnitude) is a unique characteristic of all regions of the central nervous system.

Developmental changes in carbonic anhydrase and adenylate cyclase in quaking mice

The present investigation focuses on the developmental changes in the activity and levels of carbonic anhydrase, adenylate cyclase and 3',5'-cyclic adenosine monophosphate (cAMP) in the Quaking mouse mutant in different regions of the brain. Carbonic anhydrase activity was found to be lower than normal in the forebrain of the C57/B Quaking mouse. The deficit in forebrain carbonic anhydrase was restricted to subcortical structures and was reflected equally in the membrane and soluble factions, indicating that neither pool was affected selectively. However, no difference in carbonic anhydrase activity was observed in purified myelin from Quaking and control mice. Investigation of the changes in carbonic anhydrase activity as a function of age showed a cessation in enzyme accumulation in Quaking mice at around 20 days postnatally, suggesting an abnormality in cellular development. A tritiated acetazolamide binding assay was used to quantitate the amount of enzyme present. The amount of carbonic anhydrase parallelled enzyme activity, suggesting that the defect in the Quaking animals was at the level of the control of enzyme synthesis. Similar studies on cyclic AMP metabolism showed a higher than normal adenylate cyclase activity in the upper brain stem region of Quaking mice of ages between 19 and 40 days. Adenylate cyclase activity was stimulated by norepinephrine in both control and Quaking animals. The increased adenylate cyclase activity in the Quaking mice was in contrast to a lower cyclic AMP level and could not be accounted for by an alteration in phosphodiesterase activity.