Purification and characterization of cyclic 3′5′-nucleotide phosphodiesterase D3 from Sinorhizobium fredii MAR-1

The cyclic 35-nucleotide phosphodiesterase D3 was purified from Sinorhizobium fredii MAR-1. The native enzyme had a molecular weight of approximately 44.5kDa and a subunit molecular weight of approximately 21kDa as judged by SDS-gel electrophoresis. The pH optimum of the enzyme for the hydrolysis of cyclic AMP was approximately 6.0 with both acetate and Tris-maleate buffers. The optimum temperature for hydrolysing cyclic AMP was approximately 50C. No metal ion was required for activity and EDTA up to 2.5mM did not markedly affect the enzyme. However, methylxanthines, adenine and adenosine as well as 5-AMP, ATP, ADP and metal ions like Zn²⁺, Fe²⁺, Pb²⁺, Al³⁺ and Fe³⁺, were strongly inhibitory at 2.5mM.The D3 enzyme could hydrolyse both cyclic AMP and cyclic GMP with the apparent K _m for cyclic AMP of approximately 0.23M.     

Cytochalasin B inhibits phosphoinositide hydrolysis in rat hippocampal slices

The effect of cytochalasin B on phosphoinositide (PI) hydrolysis was examined in rat hippocampal slices. Pretreatment of the slices with cytochalasin B caused a significant decrease in PI hydrolysis elicited by carbachol, norepinephrine, or by high K⁺. This effect was cytochalasin B dose- and time-dependent and was not mimicked by cytochalasin D, vinblastine, colchicine, or phloretin. In contrast, in [³H]inositol-prelabeled hippocampal membranes, cytochalasin B did not affect PI hydrolysis elicited by GTPS and GTPS plus carbachol. Similar result was obtained using the membranes prepared from the slices pretreated with cytochalasin B. The inhibitory effect of cytochalasin B on the carbachol-response was observed in SK-N-SH human neuroblastoma cells, but not in cultured rat astrocytes. These results indicate that cytochalasin B inhibits PI hydrolysis in neuron-specific manner and that its action may be an indirect cellular mechanism other than interaction with cytoskeleton elements.     

Characteristics of Cl−-dependentl-[35S]cysteic acid transport into rat brain synaptic membrane vesicles

Uptake ofl-[³⁵S]cysteic acid (L-CA) in rat synaptic membrane vesicles was investigated. Preincubation with either 10 mMl-glutamic acid (L-Glu), 25 mM L-CA, 10 mMdl-homocysteic acid, or 25 mMdl-2-amino-4-phosphonobutyrate on membrane vesicles enhanced L-[³⁵S]CA and L-[³H]Glu uptake. Na⁺ (5 mM) and omission of Cl^– from the assay medium decreased L-[³⁵S]CA uptake into both 10 mM L-Glu-loaded and non-loaded membrane vesicles. The anion transport blockers, 4-acetamide-4-isothiocyano-2,2-disulfonic acid stibene (SITS) and 4,4-diisothiocyano-2,2-disulfonic acid stilbene (DIDS), inhibited L-[³⁵S]CA uptake in a dose-dependent manner. The maximal uptake rate for L-[³⁵S]CA was decreased by 50 M SITS, while the apparent Km value of L-CA was not changed. SITS increased the EC₅₀ value of Cl^– for L-[³⁵S]CA uptake from 5 mM to 10 mM with reduction of the maximal effect. These results suggested that L-[³⁵S]CA uptake into synaptic membrane vesicles was mediated by a SITS-sensitive hetero-exchange transport with non-labeled substrates.Abbreviations SITS 4-Acetamide-4-isothiocyano-2,2-disulfonic acid stilbene - DIDS 4,4-Diisothiocyano-2,2-disulfonic acid stilbene - CA Cysteic acid - APB 2-Amino-4-phosphonobutyrate - CSA Cysteine sulfinic acid - EGTA Ethyleneglycol bis(aminoethylether) tetraacetate - GABA -Aminobutyric acid     

Desensitization of prostaglandin F2α receptor-mediated phosphoinositide hydrolysis in cultured rat astrocytes

Desensitization of prostaglandin (PG) F₂ receptor-mediated phosphoinositide (PI) hydrolysis was investigated in cultured rat astrocytes. Prolonged exposure of astrocytes differentiated by dibutyryl cyclic AMP-treatment to PGF₂ caused the desensitization of subsequent PGF₂-induced PI hydrolysis. The desensitization was time- and PGF₂ dose-dependent; maximal decrease in the PI hydrolysis was observed after exposure to 10 M PGF₂ for 4 h and the degree of the desensitization was 31.7±2.7% of control. Pretreatment with either PGD₂ or PGE₂ also induced the desensitization of subsequent PGF₂-stimulated PI hydrolysis and conversely pretreatment of PGF₂ decreased the PI responses to PGD₂ and PGE₂. The desensitization prevented by phloretin and was reversible upon removal of the agonist. Protein synthesis inhibitors blocked the recovery of the desensitization. Treatment of the cells with phorbol 12-myristate 13-acetate had no effect on the desensitization. These results suggest that prolonged exposure of the astrocytes to PGF₂ caused the desensitization of the receptors.     

HbF-Lesvos: An HbF variant due to a novel Gγ mutation (:Gγ 75 ATA→ACA) detected in a Greek family

A TC substitution at position 402 of the G globin gene results in an isoleucine to threonine substitution at codon 75 of the G globin chain and the formation of HbF-Lesvos [₂G₂ 75 (E19) IleThr].     

Substrate interactions with brain(Ca+Mg)-ATPase

ATP hydrolysis by a partially purified (Ca+Mg)-ATPase preparation from rat brain increased with substrate concentration in a biphasic fashion, with apparentK _m values of 3 M and 0.1 mM. Ca-dependent phosphorylation, however, had only a singleK _m value, 3 M. KCl increased ATPase activity in both concentration ranges, but theK _0.5 for KCl decreased from 7 mM to 0.3 mM as the ATP concentration was reduced from 1 mM to 10 M. TheK _0.5 for MgCl₂ decreased somewhat less, from 3 mM to 0.6 mM with ATP concentrations from 1 mM to 1 M, but was far lower for steady-state phosphorylation, 0.03 mM. (Ca+Mg)-dependent hydrolysis was not demonstrable with other nucleotide triphosphates or p-nitrophenyl phosphate, and these substances, as well as a reaction product, P_i, were also inhibitors. On the other hand, ADP inhibited at both ATP concentration ranges, and also stimulated dephosphorylation. This pattern of responses to substrate and cations is reminiscent of that of well-characterized transport ATPases, suggesting similar roles and mechanisms.     

Modulation of phosphoinositide metabolism in rat brain slices by excitatory amino acids,arachidonic acid,and GABA

In rat brain slices the synthesis of [³H]phosphoinositides and the production of [³H]inositol monophosphate (IP₁) induced by norepinephrine (NE) were inhibited by glutamate. Calcium concentrations were varied to test if these inhibitory effects of glutamate were mediated by a calcium-dependent process. Although reducing calcium or addition of the calcium antagonist verpamil reduced the inhibitory effects of glutamate, these results were equivocal because reduced calcium directly decreased agonist-induced [³H]phosphoinositide synthesis. The inhibitory effects of glutamate were mimicked by quisqualate in a dose-dependent manner, but none of a variety of excitatory amino acid receptor antagonists modified the inhibition caused by quisqualate. It is suggested that glutamate activates a quisqualate-sensitive receptor (for which an antagonist is not available) and causes inhibition of phosphoinositide hydrolysis mediated in part by a direct or indirect inhibitory effect of calcium on phosphoinositide synthesis. Modulatory effects of arachidonic acid were examined because glutamate and calcium can activate phospholipase A₂. Arachidonic acid caused a rapid and dose-dependent inhibition of [³H]phosphoinositide synthesis and of NE-stimulated [³H]IP₁ production. A similar inhibition of the response to carbachol also occurred. The inhibition caused by arachidonic acid was unchanged by addition of inhibitors of cyclooxygenase or lipoxygenase. Activation of phospholipase A₂ with melittin caused inhibitory effects similar to those of arachidonic acid. Inhibitors of phospholipase A₂ were found to impair phosphoinositide metabolism, likely due to their lack of specificity for phospholipase A₂. Further studies were carried out in slices that were prelabelled with [³H]inositol in an attempt to separate modulatory effects on [³H]phosphoinositide synthesis and agonist-stimulated [³H]IP₁ production. Several excitatory amino acid agonists inhibited NE-stimulated [³H]IP₁ production. This inhibitory inter-action could be due to impaired synthesis of [³H]phosphoinositides because, even though the slices were prelabeled, addition of unlabelled inositol reduced NE-stimulated [³H]IP₁ production, indicating that continuous regeneration of [³H]phosphoinositides is required. In contrast to the inhibitory effects of the excitatory amino acids, gamma-aminobutyric acid (GABA) enhanced the response to NE in cortical and hippocampal slices. GABA also enhanced the response to carbachol in hippocampal and striatal slices and to ibotenic acid in hippocampal slices. Baclofen potentiated the response to NE similarly to the effect of GABA and baclofen partially blocked the inhibitory effect of arachidonic acid but did not alter that of quisqualate.Abbreviations AMPA -amino-3-hydroxy-5-methyl-4-isoxazolepropionic - acid AP₄ dl-2-amino-4-phosphonobutyric acid - BPB bromphenacyl bromide - BSA bovine serum albumin - CNQX 6-cyano-7-nitroquinoxaline-2,3-dione - DFMO -difluoromethylornithine - DIDS diisothiocyanotostilbene-2,2-disulfonic acid - EGTA ethyleneglycol-bis-N - N, N N-tetraacetic acid - GABA -aminobutyric acid - GDEE glutamate diethyl ether - -GG -glutamylglycine - IP₁ inositol monophosphate - IP₂ inositol bisphosphate - IP₃ inositol trisphosphate - NDGA nordihydroguaiaretic acid - NE norepinephrine - NMDA N-methyl-d-aspartate     

Purification and properties of a glycerophosphocholine phosphodiesterase from bovine brain myelin

An enzyme releasing phosphocholine from glycerophosphocholine was purified to apparent homogeneity based upon SDS-PAGE. The enzyme was liberated from lyophilized bovine myelin by differential detergent extraction and final purification was accomplished with Q-Sepharose Fast Flow chromatography yielding an apparently homogenous protein. The molecular mass based upon PAGE was approximately 14 kDa. The enzyme was also capable of releasing p-nitrophenol from p-nitrophenyl-phosphocholine. Maximal activity was obtained with 0.2 mM ZnCl₂ or 1 mM CoCl₂. p-Nitrophenylphosphocholine and phosphocholine were competitive inhibitors of glycerophosphocholine hydrolysis with Ki's of 0.028 mM and 0.03 mM respectively. Glycerophosphocholine and phosphocholine were competitive inhibitors of p-nitrophenylphosphocholine hydrolysis with Ki's of 0.5 mM and 1.75 mM respectively.Abbreviations SDS-PAGE sodium dodecylsulfate polyacrylamide gel electrophoresis - GPC glycerophosphocholine - pNPPC p-nitrophenylphosphocholine - OG octyl--glucoside - PMSF phenylmethylsulfonylfluoride - CNPase 23-cyclic nucleotide 3-phosphodiesterase     

Regulation of Myo-Inositol Homeostasis in Differentiated Human NT2-N Neurons

We have investigated the possible role of second messengers on inositol homeostasis in NT2-N cells, human central nervous system neurons obtained by terminal differentiation of teratocarcinoma precursors. Uptake of inositol into NT2-N neurons was inhibited 10% by protein kinase C (PKC) activation but was unaffected by either the presence of cyclic nucleotide analogs or changes in the intracellular concentration of Ca²⁺. Efflux of inositol from NT2-N neurons was enhanced in hypotonic buffer but virtually eliminated by inclusion of the Cl^– channel blocker 4,4-diisothiocyanatostilbene-2,2-disulfonic acid, a result which indicates the involvement of a volume-sensitive organic osmolyte-anion channel. Volume-sensitive inositol efflux was stimulated 30% following activation of PKC or elevation of the cytosolic Ca²⁺ concentration but was unaffected by protein kinase A activation. These results suggest that whereas inositol uptake into NT2-N neurons is relatively refractory to regulation, volume-sensitive inositol efflux may be significantly affected by intracellular signaling events.     

Beitr?ge zum Verhalten des Krabbentauchers(Plautus alle alle)

Summary The behavior of the Little Auk(Plautus alle alle) has been studied in June/ July 1968 in West-Spitzbergen.In the shelf-area we counted 32–75 Little Auks per km² flying or swimming in the sea. Flight behavior is described. On small rocky ledges before the entrances of the breeding caves, singing, display, sleeping and preening take place. Mass singing (Massengesang), display flight and parade (Imponierflug und Imponiergehen) and billing (Schnäbeln) are described. The calls of the Little Auk consist of 5 variable elements.     

Characterization of phosphoinositide hydrolysis products induced by hexachlorocyclohexane isomers in rat brain cortex

Water-soluble inositol metabolites were separated by anion-exchange chromatogrphy in order to determine whether or not -hexachlorocyclohexane (-HCH, lindane) and related compounds affect phosphatidylinositol hydrolysis in rat brain cortex slices. Hydrolysis was increased by -and -HCH, while - and -HCH were inactive. Muscarinic receptor stimulation of rat cortical slices with carbachol increases inositol phosphates formation. The combined effect of carbachol and the hexachlorocyclohexane isomers together were approximately equal to the sum of the effect of each one separately. The results suggest that lindane stimulates phosphoinositide phospholipase C and/or inhibits the phosphases implicated in dephosphorylation of inositol phosphates.     

Moral commitment without objectivity or illusion: Comments on Ruse and Woolcock

Peter Woolcock, in Ruse's Darwinian Meta-Ethics: A Critique, argues that the subjectivist (nonobjectivist) Darwinian metaethics proposed by Michael Ruse (in Taking Darwin Seriously) cannot work, because the illusion of objectivity that Ruse claims is essential to morality breaks down when it is recognized as illusion, and there then remain no good reasons for acknowledging or following moral obligations. Woolcock, however, is mistaken in supposing that moral behaviour requires rational motivation. Ruse's Darwinian metaethical analysis shows why such objective support for morality is neither plausible nor necessary; and when that is recognized, it can also be seen that Ruse's proposed illusion of moral objectivity is superfluous.     

The Catalytic Transition State in ATP Synthase

The catalytic transition state of ATP synthase has been characterized and modeled by combined use of (1) Mg-ADP–fluoroaluminate, Mg-ADP–fluoroscandium, and corresponding Mg-IDP–fluorometals as transition-state analogs; (2) fluorescence signals of -Trp331 and -Trp148 as optical probes to assess formation of the transition state; (3) mutations of critical catalytic residues to determine side-chain ligands required to stabilize the transition state. Rate acceleration by positive catalytic site cooperativity is explained as due to mobility of -Arg376, acting as an arginine finger residue, which interacts with nucleotide specifically at the transition state step of catalysis, not with Mg-ATP- or Mg-ADP-bound ground states. We speculate that formation and collapse of the transition state may engender catalytic site / subunit-interface conformational movement, which is linked to -subunit rotation.     

Role of inositol trisphosphate as a second messenger in signal transduction processes: An essay

This essay attempts to summarize some of the best evidence for the role of inositol trisphosphate as a second messenger in signal transduction processes. The following aspects are addressed in the essay: (a) The synthesis of inositol trisphosphate and other inositol lipids, (b) Receptor-phosphatidylinositol bisphosphate phospholipase C coupling and the N-ras protooncogene, (c) Inositol trisphosphate and intracellular calcium, (d) Cell growth and oncogenes, (e) Receptors linked to the phosphatidylinositol cycle, (f) Phototransduction and (g) Interactions between inositol trisphosphate and other second messengers.Abbreviations Cyclic AMP Adenosine 3,5-cyclic monophosphate - Cyclic GMP Guanosine 3,5-cyclic monophosphate - DG sn, 1,2-Diacylglycerol - EGF Epidermal growth factor - GDP Guanosine diphosphate - GTP Guanosine triphosphate - IP Inositol 1-monophosphate - IP₂ Inositol 1,4-diphosphate - IP₃ Inositol 1,4,5-trisphosphate - PA Phosphatidic acid - PDGF Platelet-derived growth factor - PI Phosphatidylinositol - PIP Phosphatidylinositol 4-monophosphate - PIP₂ Phosphatidylinositol 4,5-bisphosphate - PIP₃ Phosphatidylinositol 3,4,5-trisphosphate - PLC Phospholipase C     

Diversity of amyloid beta protein fragment [1-40]-formed channels

1. The lipid bilayer technique was used to characterize the biophysical and pharmacological properties of several ion channels formed by incorporating amyloid beta protein fragment (AP) 1–40 into lipid membranes. Based on the conductance, kinetics, selectivity, and pharmacological properties, the following AP[1–40]-formed ion channels have been identified: (i) The AP[1–40]-formed bursting fast cation channel was characterized by (a) a single channel conductance of 63 pS (250/50 mM KCl cis/trans) at +140 mV, 17 pS (250/50 mM KCl cis/trans) at –160 mV, and the nonlinear current–voltage relationship drawn to a third-order polynomial, (b) selectivity sequence P _K > P _Na > P _Li = 1.0:0.60:0.47, (c) P_o of 0.22 at 0 mV and 0.55 at +120 mV, and (d) Zn²⁺-induced reduction in current amplitude, a typical property of a slow block mechanism. (ii) The AP[1–40]-formed spiky fast cation channel was characterized by (a) a similar kinetics to the bursting fast channel with exception for the absence of the long intraburst closures, (b) single channel conductance of 63 pS (250/50 KCl) at +140 mV 17 pS (250/50 KCl) at –160 mV, the current–voltage relationship nonlinear drawn to a third-order polynomial fit, and (c) selectivity sequence P _Rb > P _K > P _Cs > P _Na > P _Li = 1.3:1.0:0.46:0.40:0.27. (iii) The AP[1–40]-formed medium conductance channel was charcterized by (a) 275 pS (250/50 mM KCl cis/trans) at +140 mV and 19 pS (250/50 mM KCl cis/trans) at –160 mV and (b) inactivation at V_ms more negative than –120 and more positive than +120 mV. (iv) The AP[1–40]-formed inactivating large conductance channel was characterized by (a) fast and slow modes of opening to seven multilevel conductances ranging between 0–589 pS (in 250/50 mM KCl) at +140 mV and 0–704 pS (in 250/50 mM KCl) at –160 mV, (b) The fast mode which had a conductance of <250 pS was voltage dependent. The inactivation was described by a bell-shaped curve with a peak lag time of 7.2 s at +36 mV. The slow mode which had a conductance of >250 pS was also voltage dependent. The inactivation was described by a bell-shaped curve with a peak lag time of 7.0 s at –76 mV, (c) the value of P _K/P _choline for the fast mode was 3.9 and selectivity sequence P _K > P _Cs > P _Na > P _Li = 1.0:0.94:0.87:0.59. The value of P _K/P _choline for the slow mode was 2.7 and selectivity sequence P _K > P _Na > P _Li > P _Cs = 1.0:0.59:0.49:0.21, and (d) asymmetric blockade with 10 mM Zn²⁺-induced reduction in the large conductance state of the slow mode mediated via slow block mechanism. The fast mode of the large conductance channel was not affected by 10 mM Zn²⁺.2. It has been suggested that, although the bursting fast channel, the spiky fast channel and the inactivating medium conductance channel are distinct, it is possible that they are intermediate configurations of yet another configuration underlying the inactivating large conductance channel. It is proposed that this heterogeneity is one of the most common features of these positively-charged cytotoxic amyloid-formed channels reflecting these channels ability to modify multiple cellular functions.3. Furthermore, the formation of -sheet based oligomers could be an important common step in the formation of cytotoxic amyloid channels.     

Evolution of the single copyαA-crystallin gene: differently sized mRNAs of mammals and birds show homology in their 3′ non-coding regions

A-Crystallin, a major structural polypeptide of the vertebrate eye lens, is evolutionarily highly conserved. We have analyzed the corresponding nucleic acid sequences in both genomic DNA digests as well as in lens cytoplasmic RNA preparations from a wide variety of vertebrates by blot hybridization with cloned rat A₂-crystallin cDNA probes. The probes are not able to hybridize under any conditions to RNA and DNA derived from fishes and amphibia, but do show substantial homology with the sequences of mammals, birds and reptiles. The A-crystallin gene, which has been isolated from a hamster gene library occurs only once in the haploid genome. Coding and 3-untranslated regions of A₂-crystallin mRNA are conserved among all mammals and birds examined. However, the regions comprising the conserved sequences are differently represented in the ultimate mRNA. The A₂-mRNA 3-non-coding regions of reptiles and birds are 300–550 bases longer than those of mammals. Some rodents produce next to the A₂-mRNA another messenger that encodes the A^lns-polypeptide possessing an insertion of 22/23 amino acid residues between positions 63 and 64 of the A₂-polypeptide chain. A₂ and A^lns-mRNA are generated from a single gene as major and minor species, respectively, in a proportion which is similar to the ratio of the polypeptides foundin vivo andin vitro. The size heterogeneity of the A₂-mRNA from most mammals examined is due to the variable size of the poly(A) tail.     

Effects of β-phenylethylamine on polyphosphoinositide turnover in rat cerebral cortex

The effects of the trace amine, -phenylethylamine, on the hydrolysis of inositol phospholipids in rat cerebral cortical slices was studied using a direct assay involving prelabeling with [³H]inositol and then examining the production of [³H]inositol phosphates in the presence of lithium. Phenylethylamine exhibited two different effects. Millimolar concentrations of phenylethylamine stimulated the production of [³H]inositol phosphates to about 200% of control, while much smaller concentrations (micromolar) inhibited noradrenaline(NE)-stimulated [³H]inositol phosphate formation dose-dependently. The ₁-antagonist, prazosin, inhibited the increases in [³H]polyphosphoinositide turnover stimulated by phenylethylamine and by NE, though it inhibited phenylethylamine to a lesser extent than NE. It appears, therefore, that phenylethylamine affects [³H]inositol phosphate formation by acting as a partial ₁-agonist.     

Metabolic formation of dodecanedioic acid from n-dodecane by a mutant of Candida tropicalis

Summary These experiments studied the metabolic formation of a,-dodecanedioic acid using the mutant S 76 developed from the wild strain Candida tropicalis 1230 (capable of producing large amounts of a,-dodecanedioic acid).Our results show for the first time that 12-hydroxydodecanoic acid was excreted into the medium as a free acid.n-Dodecanol and n-dodecanoic acid were also detected in the n-dodecane medium. The mutant S 76 was able to produce a,-dodecanedioic acid using either n-dodecanol or dodecanoic acid as the sole carbon source. Quantitative cahnges in the concentrations of 12-hydroxy-dodecanoic acid and other intermediates were recorded during the formation of a,-dodecanedioic acid. S 76 was rapidly able to convert large amounts of 12-hydroxy-dodecanoic acid to a,-dodecanedioic acid.The formation of a,-dodecanedioic acid from n-dodecane via the sequence n-dodecanoln-dodecanoic acid 12-hydroxy-dodecanoic acid was confirmed.     

Calcium oscillation and phosphatidylinositol 3-kinase positively regulate integrin α<Subscript>IIb</Subscript>β<Subscript>3</Subscript>-mediated outside-in signaling

Summary The frequency of calcium oscillation reveals the platelet activation status, however, the biological significance of the periodic calcium responses and methods of communication with other integrin-mediated signals are not clear. RGD-containing disintegrin rhodostomin coated substrates were employed to enhance platelet spreading and calcium oscillation through direct binding and clustering of the receptor integrin _IIb3. The results showed that the activation of phosphatidylinositol 3-kinase (PI3-K) and internal calcium pathways were crucial for _IIb3 outside-in signaling. PI3-K antagonists wortmannin and LY294002 inhibited disintegrin substrates and induced platelet spreading and calcium oscillation. At the same time, pretreatment of platelets with the microsomal calcium–ATPase inhibitor thapsigargin to deplete internal calcium stores severely impaired the calcium oscillation as well as PI3-K activation and spreading on disintegrin substrates. Because inhibition of one pathway could inhibit the other, our data indicates that PI3-K and calcium oscillation are synergistically operated and form a positive-feedback regulation in integrin _IIb3-mediated outside-in signaling.     

Polyphosphoinositide mono- an diphosphoesterases of three subfractions of rat brain myelin

Phosphomonoesterase and diesterase that cleave phosphatidylinositol-4-phosphate (diphosphoinositide, DPI) and phosphatidylinositol-4,5-bisphosphate (triphosphoinositide, TPI) were detected in three subfractions of purified rat brain myelin, and some properties of the enzymes were studied. Monoesterase activity was stimulated by KCl, maximally at a concentration of 25 mM, and inhibited at KCl concentrations above 50 mM. Addition of boiled pH 5 supernatant of rat brain homogenate doubled the enzymic activity; EDTA was inhibitory. The specific activities were nearly equal in the low density, medium density, and heavy density myelin fractions but about 30% lower than in whole brain homogenate. The monophosphatase could be solubilized by extraction with 0.2% Triton X-100. The phosphodiesterase activity was inhibited by EDTA and EGTA and not stimulated by KCl or pH 5 supernatant. Specific activities were nearly equal in whole brain and myelin but were by about 60 percent elevated in the heavy density over the low density myelin fraction. These results show that the hydrolases operative in the fast turnover of the inositide phosphate groups are distributed over the entire myelin structure.