Formation of a New Biogenic Aldehyde Adduct by Incubation of Tryptamine with Rat Brain Tissue

Tryptamine was degraded by incubation with rat brain homogenate to an unknown product. The reaction was stimulated by the nonionic detergents Triton X-100 and Lubrol PX and less by the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]1-propanesulfonate (CHAPS). The same results were obtained with pig brain and bovine brain. The monoamine oxidase inhibitor pargyline inhibited the reaction strongly, indicating the participation of the enzyme on the reaction. Addition of 17,000 g supernatant from rat brain homogenate increased the formation effectively whereas phospholipids or chloroform/methanol (7:3) extract from the 17,000 g supernatant showed only little or no effect. Chromatographic and electrophoretic properties as well as the chemical reaction of the product with specific reagents suggest that the compound consists of an indole part and an amino acid part. The product could be identified by fast atom bombardment mass spectrometry and by comparison with the synthetic substance (4R)-2-(3-indolylmethyl)-1,3-thiazolidine-4-carboxylic acid. It is formed by the enzymatic oxidation of tryptamine producing indole-3-acetaldehyde which spontaneously cyclizes with free L-cysteine from the tissue. The results suggest that the reaction of biogenic aldehydes with brain macromolecules may proceed via an analogous reaction.     

Formation of Thiazolidine-4-Carboxylic Acid Represents a Main Metabolic Pathway of 5-Hydroxytryptamine in Rat Brain

Incubation of 5-hydroxytryptamine (5-HT) with rat brain homogenate resulted in the formation of (4R)-2-[3'-(5'-hydroxyindolyl)-methyl]-1,3-thiazolidine-4-carboxyl ic acid (5'-HITCA) as the major metabolite. The substance represents the condensation product of 5-hydroxyindole-3-acetaldehyde with L-cysteine. The chemical structure was confirmed by chromatographic and chemical methods as well as by fast atom bombardment mass spectrometry. Incubation of 5-HT in the presence of L-cysteine yielded the thiazolidine as the main metabolite up to 4 h. Under these conditions, the concentration of 5-hydroxyindole-3-acetic acid (5-HIAA) amounted to about 20% and 57% of 5'-HITCA (0.5 h and 4 h, respectively). In contrast to these findings, indole-3-acetic acid (IAA) was identified as the major metabolite when tryptamine was incubated under similar conditions. (4R)-2-(3'-Indolylmethyl)-1,3-thiazolidine-4-carboxylic acid (ITCA) was found to be the main conversion product of tryptamine only during the first 30 min. To investigate the fate of the thiazolidines, radiolabelled and unlabelled ITCA was incubated with rat brain homogenate. The compound was degraded enzymatically and rapidly. Subcellular fractionation revealed that the enzyme activity was present mainly in the cytosolic fraction whereas the preparation of mitochondria showed less activity. The responsible enzyme is presumably a carbon-sulfur lyase (EC 4.4.1.-). The major metabolite was isolated by HPLC and identified by mass spectrometry as well as by comparison with reference compounds to be IAA.(ABSTRACT TRUNCATED AT 250 WORDS)     

FACTORS INFLUENCING BRAIN AND TISSUE LEVELS OF TRYPTAMINE: SPECIES, DRUGS AND LESIONS

With a modification of the spectrophotofluorometric (SPF) method of HESS & UDENFRIEND (1959) (J. Pharmac. exp. Ther. 127 , 175-177), brain tryptamine levels in the rat (20.9 ng/g) and guinea-pig (20.7 ng/g) were found to be less than those in the dog (32.1 ng/g) and cat (52.2 ng/g). Regional distribution studies in the dog and cat showed that tryptamine was present in all major brain regions with highest concentrations in the spinal cord. Blood levels of tryptamine in the guinea-pig, dog and cat (6-7 ng/ml) were lower than brain levels. Pargyline significantly increased brain tryptamine in both the dog and cat; whereas, isocarboxazid (after 4 h) increased brain tryptamine levels in the dog but decreased brain levels in the cat. Reserpine (0.5-1.0 mg/kg per day for 1-4 days) did not significantly decrease brain, spinal cord or blood tryptamine levels in the dog. Spinal cord transection did not decrease tryptamine levels below the lesion in the chronic spinal dog.     

Region-Selective Decreases in Densities of [3H]Tryptamine Binding Sites in Autopsied Brain Tissue from Cirrhotic Patients with Hepatic Encephalopathy

Abstract: The distribution of [³H]tryptamine binding sites, in autopsied brain tissue from cirrhotic patients with hepatic encephalopathy (HE) and an equal number of age-matched control subjects free from hepatic, neurological, or psychiatric disorder, was investigated. Scatchard analysis demonstrated a heterogeneous distribution for this binding site, with the highest density being observed in hippocampus ≫ frontal cortex = caudate nucleus > temporal cortex = cerebellum. When comparing [³H]-tryptamine binding site densities in control brain tissue with that in brain tissue from patients with HE, significant decreases in densities were observed in the frontal cortex (by 56%, p < 0.001), hippocampus (by 43%, p < 0.001), and caudate nucleus (by 41%, p < 0.01) of the HE group. Binding site affinities were within normal limits. The findings of decreased densities of [³H]tryptamine binding sites taken in conjunction with previous reports of increased CSF and brain tryptamine concentrations in HE suggest a pathogenic role for this neuroactive amine in HE resulting from chronic liver failure.     

Uptake of 13C-Tracer Arachidonate and γ-Linolenate by the Brain and Liver of the Suckling Rat Observed Using 13C-NMR

Arachidonic acid (AA; 20:4n-6) is one of the principal components of the phosphoglycerides in neural cell membranes. During the critical period of postnatal development in mammals, AA is supplied preformed, directly from the milk or derived from precursor fatty acids such as gamma-linolenic acid (GLA; 18:3n-6). In this study, 13C-NMR spectroscopy was applied to investigate the incorporation of [1-(13)C]AA and [3-(13)C]GLA into liver and brain lipids of 7-15-day-old rats. The main objective was to establish the importance of dietary GLA for tissue AA accretion relative to the contribution from preformed dietary AA. [1-(13)C]AA and [3-(13)C]GLA were injected into the stomach of 7-day-old rats as a mixture. 13C-NMR spectroscopy of lipid extracts revealed incorporation of [1-(13)C]AA and [5-(13)C]AA (the latter derived from metabolism of the injected [3-(13)C]GLA) into phosphoglycerides and triacylglycerols. Preformed AA was 10 (liver)-17 (brain) times more efficient in contributing to tissue AA than AA derived from precursor GLA. In separate experiments, NMR spectroscopy was used to assess uptake of [1-(13)C]AA directly in living rats and intact organs. Results showed that intact liver and brain contain an appreciable amount of NMR-detectable lipids. The in vivo/in vitro information obtained from organs provided details on the mobility and turnover of tissue lipids.     

Determination of endogeneous indoleacetic acid and tryptophol in mouse brain by high performance liquid chromatography with fluorometric detection

A simple and sensitive method using high performance liquid chromatography with fluorometric detection has been developed for the identification and quantitation of the endogeneous tryptamine metabolites, indoleacetic acid (IAA) and tryptophol (TOL) in the normal mouse brain. The limits of sensitivity are 5pg for both IAA and TOL. The extract procedure from the brain is only to deproteinize samples. The mean concentrations of IAA and TOL in the mouse brain are 8.99 +/- 0.31 ng/g and 3.56 +/- 0.21 ng/g respectively. The effects of pargyline and tryptamine on the levels of IAA and TOL were also studied.     

Synthesis of some new hybride molecules containing several azole moieties and investigation of their biological activities

1,2,4-Triazole-3-one prepared from tryptamine was converted to the corresponding carbothioamides by several steps. Their treatment with ethyl bromoacetate or 4-chlorophenacyl bromide produced the corresponding 5-oxo-1,3-thiazolidine or 3-(4-chlorophenyl)-1,3-thiazole derivatives. Acetohydrazide derivative that was obtained starting from tryptamine, was converted to the corresponding Schiff basis and sulfonamide by the treatment with suitable aldehydes and benzensulphonyl chloride, respectively. 2-[(4-Amino-5-thioxo-4,5-dihydro-1H-1,2,4-triazole-3-yl)methyl]-4-[2-(1H-indole-3-yl)ethyl]-5-methyl-2,4-dihydro-3H-1,2,4-triazole-3-one was synthesized starting from hydrazide via the formation of the corresponding 1,3,4-oxadiazole compound, while the other bitriazole compounds were obtained by intramolecular cyclisation of carbothioamides in basic media. The treatment of 1,2,4-triazole or 1,3,4-oxadiazole compound with several amines generated the corresponding Mannich bases. Ethyl (2-amino-1,3-thiazole-4-yl)acetate was converted to the corresponding 1,3,4-oxadiazole derivative, arylidenehydrazides, 1,2,4-triazole-3-one and 5-oxo-1,3-oxazolidine derivatives by several steps. The structural assignments of new compounds were based on their elemental analysis and spectral (FT IR, ¹H NMR, ¹³C NMR and LC-MS) data. The antimicrobial, antilipase and antiurease activity studies revealed that some of the synthesized compounds showed antimicrobial, antilipase and/or antiurease activity.     

Isolation and identification of lipoxygenase products from the rat central nervous system

Leukotrienes B4, C4, D4 and E4, together with five monohydroxyeicosatetraenoic acids, were isolated after incubation of chopped rat brain tissue with ionophore A23187. The monohydroxyeicosatetraenoic acids were 5-hydroxy-6,8,11,14-eicosatetraenoic acid, 9-hydroxy-5,7,11,14-eicosatetraenoic acid, 11-hydroxy-5,8,12,14-eicosatetraenoic acid, 12-hydroxy-5,8,10,14-eicosatetraenoic acid and 15-hydroxy-5,8,11,13-eicosatetraenoic acid. Identification of the compounds was performed using reversed-phase high-performance liquid chromatography, ultraviolet spectroscopy and gas chromatography-mass spectrometry. Formation of the compounds was inhibited by micromolar concentrations of nordihydroguaiaretic acid. Indomethacin specifically inhibited the formation of 11-hydroxy-5,8,12,14-eicosatetraenoic acid, suggesting that this compound was produced as a by-product during cyclooxygenase-catalyzed prostaglandin synthesis.     

A novel fluorinated tryptamine with highly potent serotonin 5-HT1A receptor agonist properties

Synthesis and biological evaluation of a novel fluorinated tryptamine analogue are described. This new compound 1-(4-fluoro-5-methoxyindol-3-yl)pyrrolidine (2) was found to be a potent serotonin 5-HT1A agonist.     

[3H]Tryptamine Binding Sites Are Not Identical to Monoamine Oxidase in Rat Brain

Competition binding studies, subcellular distribution, and in vitro autoradiography were employed to compare the binding in rat brain of [3H]tryptamine with two radioligands for monoamine oxidase (MAO), [3H]pargyline, and [3H]1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine ([3H]MPTP). The MAO inhibitors pargyline, clorgyline, and deprenyl all yielded biphasic competition curves versus [3H]tryptamine. At low concentrations, these drugs stimulated binding by protecting the radioligand from MAO oxidation; at considerably higher concentrations, they inhibited binding by direct competition at the [3H]tryptamine binding site. In subcellular distribution studies, [3H]tryptamine was localized preferentially to the synaptosomal fraction, whereas [3H]pargyline showed greater binding to the mitochondrial fraction. Equilibrium binding studies revealed that the potencies of a series of seven compounds at inhibiting [3H]tryptamine binding were completely different from their potencies at inhibiting [3H]MPTP binding. Finally, the autoradiographic distribution of [3H]tryptamine binding in rat brain was different from that of [3H]MPTP and [3H]pargyline. We conclude that the [3H]tryptamine binding site in rat brain is not equivalent to MAO.     

Tyrosine kinase inhibitors from the rainforest tree Polyscias murrayi

A series of 3-(4-hydroxyphenyl) propanoic acid derivatives, which inhibit Itk (interleukin-2 inducible T-cell kinase), a Th2-cell target, were isolated from the Australian rainforest tree Polyscias murrayi. The new compound 3-(4-hydroxyphenyl) propionyl choline and a 2:1 mixture of the new compounds 3,4-di-O-3-(4-hydroxyphenyl) propionyl-1,5-dihydroxycyclohexanecarboxylic acid and 3,5-di-O-3-(4-hydroxyphenyl) propionyl-1,4-dihydroxycyclohexanecarboxylic acid were isolated along with two known compounds 3-(4-hydroxyphenyl) propanoic acid and 3-(3,4-hydroxyphenyl) propanoic acid. Their structures were determined by 1D and 2D NMR spectroscopy. The assay results suggest that both the 3-(4-hydroxyphenyl) propanoate and carboxyl moieties contribute to Itk activity of the compounds.     

Structural characterization of tatiopterin, a novel pterin isolated from Methanogenium tationis

Cofactor extracts of Methanogenium tationis were screened for the presence of pterin-derivatives. Methanopterin, sarcinapterin and 7-methylpterin were absent, while 2-amino-4-hydroxy-pteridine and another blue fluorescent compound with a pterin spectrum were detected. The latter pterin was purified by ion exchange and reversed-phase column chromatography. The structure of this compound was elucidated by combining spectrophotometry, amino acid analysis and 1H-NMR spectroscopy. The pterin, which we named tatiopterin, was identified as an aspartyl derivative of sarcinapterin with a 7-proton instead of a 7-methyl group in the pterin moiety. The IUPAC name is: N-[-1'-(2'-amino-4'-hydroxy-7'-proton-6'-pteridinyl)ethyl]-4- [2',3',4',5'-tetrahydroxypent-1'-yl(5'----1')O-alpha- ribofuranosyl-5'-phosphoric acid]aniline, in which the phosphate group is esterified with alpha-hydroxyglutarylglutamylaspartic acid.     

Presence of 3-Hydroxyanthranilic Acid in Rat Tissues and Evidence for Its Production from Anthranilic Acid in the Brain

As assessed by HPLC with electrochemical detection, 3-hydroxyanthranilic acid (3-HANA) was found to be present in the rat brain and peripheral organs. The highest concentrations were measured in the kidney (86 fmol/mg of tissue) and spleen (56 fmol/mg of tissue), whereas the adrenal gland, liver, heart, and several forebrain areas (hippocampus, striatum, parietal cortex, thalamus, amygdala/pyriform cortex, and frontal cortex) contained less 3-HANA (between 15 and 22 fmol/mg of tissue). Slightly lower concentrations of 3-HANA were found in the brainstem and the cerebellum. The metabolic disposition of 3-HANA was examined in tissue slices which were incubated in Krebs-Ringer buffer at 37 degrees C in vitro. Incubation for up to 2 h did not affect 3-HANA concentration in brain tissue. However, inhibition of 3-HANA degradation by the specific 3-hydroxyanthranilic acid oxygenase blocker 4-chloro-3-hydroxyanthranilic acid (4-Cl-3-HANA; 10 microM) resulted in a rapid (within 2.5 min) doubling of 3-HANA levels in slices from cerebral cortex. No further increases were observed after incubations of up to 120 min. Exposure of cortical slices to 3-HANA's putative bioprecursors, 3-hydroxykynurenine (3-HK) and anthranilic acid (ANA), in the absence of 4-Cl-3-HANA resulted in rapid, transient increases in 3-HANA production. Maximal 3-HANA synthesis from ANA exceeded the maximal effect of 3-HK by approximately 11-fold.2+ In the presence of 4-Cl-3-HANA, 1 mM ANA produced 9.0 +/- 0.3 and 89.0 +/- 9.3 (5 min) or 51.6 +/- 7.9 and 187.5 +/- 11.2 (120 min) fmol of newly synthesized 3-HANA/mg of brain tissue, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Formation of novel D-ring and E-ring isoprostane-like compounds (D4/E4-neuroprostanes) in vivo from docosahexaenoic acid

Free radical-mediated oxidant injury and lipid peroxidation have been implicated in a number of neural disorders. We have reported that bioactive prostaglandin D2/E2-like compounds, termed D2/E2-isoprostanes, are produced in vivo by the free radical-catalyzed peroxidation of arachidonic acid. Docosahexaenoic acid, in contrast to arachidonic acid, is the most abundant unsaturated fatty acid in brain. We therefore questioned whether D/E-isoprostane-like compounds (D4/E4-neuroprostanes) are formed from the oxidation of docosahexaenoic acid. Levels of putative D4/E4-neuroprostanes increased 380-fold after oxidation of docosahexaenoic acid in vitro from 15.2 +/- 6.3 to 5773 +/- 1024 ng/mg of docosahexaenoic acid. Subsequently, chemical approaches and liquid chromatography electrospray ionization tandem mass spectrometry definitively identified these compounds as D4/E4-neuroprostanes. We then explored the formation of D4/E4-neuroprostanes from a biological source, rat brain synaptosomes. Basal levels of D4/E4-neuroprostanes were 3.8 +/- 0.6 ng/mg of protein and increased 54-fold after oxidation (n = 4). We also detected these compounds in fresh brain tissue from rats at levels of 12.1 +/- 2.4 ng/g of brain tissue (n = 3) and in human brain tissue at levels of 9.2 +/- 4.1 ng/g of brain tissue (n = 4). Thus, these studies have identified novel D/E-ring isoprostane-like compounds that are derived from docosahexaenoic acid and that are formed in brain in vivo. The fact that they are readily detectable suggests that ongoing oxidative stress is present in the central nervous system of humans and animals. Further, identification of these compounds provides a rationale for examining their role in neurological disorders associated with oxidant stress.     

Isolation and identification of β-citryl-L-glutamic acid from newborn rat brain

Ab unknwon compound containing glutamic acid residue was found in newborn rat brain. The compound occurred predominantly in brain. Its concentration was approx. 1 μmol/g tissue at birth and decreased to one-tenth 24 days after birth.The compound was isolated from newborn rat brains, and subjected to elementary analysis and to infrared and mass spectrometric analysis. Glutamic acid and citric acid were formed from the compound on acid hydrolysis. The compound was presumed to be a citryglutamic acid.Two isomers, α- and β-citrylglutamic acid, were sunthesized. The unknown compound was identified as β-citryl-L-glutamic acid. The occurrence of this compound has not been reported in nature.     

AN ASSAY PROCEDURE FOR TRYPTAMINE IN BRAIN AND SPINAL CORD USING ITS [3H]DANSYL DERIVATIVE

—The tryptamine content of rat and mouse brain and spinal cord was determined with a radiochemical derivative assay, using [³H]dansyl chloride. The amine was extracted into toluene-isoamyl alcohol, back-extracted into dilute acid, then adsorbed onto a non-ionic polystyrene resin, and dansylated in tetrahydrofuran after elution from the resin. Optimum recoveries were obtained with TCA extracts, although significant losses occurred due to surface adsorption and protein binding. The brain content of tryptamine increased after MAO inhibition and was not significantly further increased when tryptophan loading was combined with inhibition of MAO and/or tryptophan 5-hydroxylase. The tryptamine concentration of spinal cord exceeded that of brain and increased rapidly after death. Among brain regions tryptamine concentrations were greatest in hypothalamus and striatum and lowest in cerebral cortex and cerebellum.     

Transplacental pharmacokinetics and fetal distribution of 2', 3'-didehydro-3'-deoxythymidine (d4T) and its metabolites in late-term rhesus macaques

BACKGROUND: The overall goal of human immunodeficiency virus (HIV) therapy during pregnancy is to maintain maternal health and reduce the probability of vertical transmission during gestation and delivery, while keeping toxicity risks low. Azidothymidine (AZT) is currently recommended for pregnant women infected with HIV; however, many pregnant women are unable to tolerate AZT because of toxicity. In the present study, the placental transfer and fetal accumulation of the anti-HIV compound 2',3'-didehydro-3'-deoxythymidine (d4T) and its active (triphosphorylated) and inactive (thymine and beta-aminoisobutyric acid) metabolites were examined at steady state in late-term rhesus macaques. METHODS: On the day of the hysterotomy, the mother was administered an intravenous loading dose of d4T, followed by a 3-hr steady-state intravenous infusion that also included [(3)H]d4T as a tracer. After 3 hr of infusion, the fetus was delivered by cesarean section under halothane/N(2)O anesthesia. Plasma, amniotic fluid, and tissues were analyzed for d4T and its inactive metabolites by HPLC; tissue samples were analyzed for d4T and active (phosphorylated) metabolites by strong anion-exchange HPLC. RESULTS: Maternal steady-state plasma concentrations of d4T were 1-2 microg/ml, with a fetal-to-maternal plasma ratio of 0.85 +/- 0.09. The fetal tissue distribution of radioactivity was highest in the kidney and lowest in the brain. D4T, thymine, and beta-aminoisobutyric acid were detected in all fetal tissues examined. CONCLUSIONS: Our data indicate that d4T readily crosses the placenta and is present in the fetus as parent compound or its inactive metabolites after maternal infusion. Although fetal plasma concentrations of d4T were similar to clinical d4T concentrations, no phosphorylated metabolites were detected. Teratology 62:93-99, 2000. Published 2000 Wiley-Liss, Inc.     

A novel immunosensor based on an alternate strategy of electrodeposition and self-assembly

An imprinted electrochemical sensor based on polypyrrole-sulfonated graphene (PPy-SG)/hyaluronic acid-multiwalled carbon nanotubes (HA-MWCNTs) for sensitive detection of tryptamine was presented. Molecularly imprinted polymers (MIPs) were synthesized by electropolymerization using tryptamine as the template, and para-aminobenzoic acid (pABA) as the monomer. The surface feature of the modified electrode was characterized by cyclic voltammetry (CV). The proposed sensor was tested by chronoamperometry. Several important parameters controlling the performance of the molecularly imprinted sensor were investigated and optimized. The results showed that the PPy-SG composites films showed improved conductivity and electrochemical performances. HA-MWCNTs bionanocomposites could enhance the current response evidently. The good selectivity of the sensor allowed three discriminations of tryptamine from interferents, which include tyramine, dopamine and tryptophan. Under the optimal conditions, a linear ranging from 9.0×10(-8) mol L(-1) to 7.0×10(-5) mol L(-1) for the detection of tryptamine was observed with the detection limit of 7.4×10(-8) mol L(-1) (S/N=3). This imprinted electrochemical sensor was successfully employed to detect tryptamine in real samples.     

Bioconversion of 3beta-hydroxy-5-cholenoic acid into chenodeoxycholic acid by rat brain enzyme systems

We have previously demonstrated that the rat brain contains three unconjugated bile acids, and chenodeoxycholic acid (CDCA) is the most abundantly present in a tight protein binding form. The ratio of CDCA to the other acids in rat brain tissue was significantly higher than the ratio in the peripheral blood, indicating a contribution from either a specific uptake mechanism or a biosynthetic pathway for CDCA in rat brain. In this study, we have demonstrated the existence of an enzymatic activity that converts 3beta-hydroxy-5-cholenoic acid into CDCA in rat brain tissue. To distinguish marked compounds from endogenous related compounds, 18O-labeled 3beta-hydroxy-5-cholenoic acid, 3beta,7alpha-dihydroxy-5-cholenoic acid, and 7alpha-hydroxy-3-oxo-4-cholenoic acid were synthesized as substrates for in vitro incubation studies. The results clearly suggest that 3beta-hydroxy-5-cholenoic acid was converted to 3beta,7alpha-dihydroxy-5-cholenoic acid by microsomal enzymes. The 7alpha-hydroxy-3-oxo-4-cholenoic acid was produced from 3beta,7alpha-dihydroxy-5-cholenoic acid by the action of microsomal enzymes, and Delta4-3-oxo acid was converted to CDCA by cytosolic enzymes. These findings indicate the presence of an enzymatic activity that converts 3beta-hydroxy-5-cholenoic acid into CDCA in rat brain tissue. Furthermore, this synthetic pathway for CDCA may relate to the function of 24S-hydroxycholesterol, which plays an important role in cholesterol homeostasis in the body.     

ENZYMATIC FORMATION OF TETRAHYDRO-β-CARBOLINE FROM TRYPTAMINE AND 5-METHYLTETRAHYDROFOLIC ACID IN RAT BRAIN FRACTIONS: REGIONAL AND SUBCELLULAR DISTRIBUTION

—In rat brain extract tryptamine is converted to 1,2,3,4-tetrahydro-β-carboline (THβJC) and N-methyltryptamine to 2-methyl-THβC in the presence of 5-methyltetrahydrofolic acid. We believe this occurs through enzymatic conversion of 5-methyltetrahydrofolic acid to formaldehyde and tetrahydrofolic acid, followed by spontaneous condensation of the radioactive formaldehyde with the substrate tryptamine (Donaldson & Keresztesy , 1961). The final products of the reactions have been identified by both thin layer chromatography and mass spectrophotometry. Subcellular fractionation shows more than 90 per cent of the formaldehyde-forming enzyme activity to be in the cytosol. Specific activities in fractions from 16 discrete regions of the brain and CNS range from 210·2 ± pmol of THβC/mg protein/h in corpus striatum to 62·9 ± 3·6 pmol of THβC/mg protein/h in corpus callosum.