Effect of tissue specificity of brain soluble fractions on Na+, K+-ATPase activity

Previous evidence from this laboratory indicated that catecholamines and brain endogenous factors modulate Na⁺, K⁺-ATPase activity of the synaptosomal membranes. The filtration of a brain total soluble fraction through Sephadex G-50 permitted the separation of two fractions-peaks I and II-which stimulated and inhibited Na⁺, K⁺-ATPase, respectively (Rodríguez de Lores Arnaiz and Antonelli de Gomez de Lima, Neurochem. Res.11, 1986, 933). In order to study tissue specificity a rat kidney total soluble was fractionated in Sephadex G-50 and kidney peak I and II fractions were separated; as control, a total soluble fraction prepared from rat cerebral cortex was also processed. The UV absorbance profile of the kidney total soluble showed two zones and was similar to the profile of the brain total soluble. Synaptosomal membranes Na⁺, K⁺- and Mg²⁺-ATPases were stimulated 60–100% in the presence of kidney and cerebral cortex peak I; Na⁺, K⁺-ATPase was inhibited 35–65% by kidney peak II and 60–80% by brain peak II. Mg²⁺-ATPase activity was not modified by peak II fractions. ATPases activity of a kidney crude microsomal fraction was not modified by kidney peak I or brain peak II, and was slightly increased by kidney peak II or brain peak I. Kidney purified Na⁺, K⁺-ATPase was increased 16–20% by brain peak I and II fractions. These findings indicate that modulatory factors of ATPase activity are not exclusive to the brain. On the contrary, there might be tissue specificity with respect to the enzyme source.     

Effect of ruthenium complexes on the activities of succinate dehydrogenase and cytochrome oxidase

In this article, we report the effects of acute administration of ruthenium complexes, trans-[RuCl(2)(nic)(4)] (nic=3-pyridinecarboxylic acid) 180.7 micromol/kg (complex I), trans-[RuCl(2)(i-nic)(4)] (i-nic=4-pyridinecarboxylic acid) 13.6 micromol/kg (complex II), trans-[RuCl(2)(dinic)(4)] (dinic=3,5-pyridinedicarboxylic acid) 180.7 micromol/kg (complex III) and trans-[RuCl(2)(i-dinic)(4)]Cl (i-dinic=3,4-pyridinedicarboxylic acid) 180.7 micromol/kg (complex IV) on succinate dehydrogenase (SDH) and cytochrome oxidase (COX) activities in brain (hippocampus, striatum and cerebral cortex), heart, skeletal muscle, liver and kidney of rats. Our results showed that complex I inhibited SDH activity in hippocampus, cerebral cortex, heart and liver; and inhibited COX in heart and kidney. Complex II inhibited SDH in heart and hippocampus; COX was inhibited in hippocampus, heart, liver and kidney. SDH activity was inhibited by complex III in heart, muscle, liver and kidney. However, COX activity was increased in hippocampus, striatum, cerebral cortex and kidney. Complex IV inhibited SDH activity in muscle and liver; COX activity was inhibited in kidney and increased in hippocampus, striatum and cerebral cortex. In a general manner, the complexes tested in this work decrease the activities of SDH and COX in heart, skeletal muscle, liver and kidney. In brain, complexes I and II were shown to be inhibitors and complexes III and IV activators of these enzymes. In vitro studies showed that the ruthenium complexes III and IV did not alter COX activity in kidney, but activated the enzyme in hippocampus, striatum and cerebral cortex, suggesting that these complexes present a direct action on COX in brain.     

Post-proline cleaving enzyme. Synthesis of a new fluorogenic substrate and distribution of the endopeptidase in rat tissues and body fluids of man.

Synthesis and application of the first fluorogenic substrate, N-carbobenzoxyglycylprolyl-4-methylcoumarinyl amide (Z-Gly-Pro-MeCouNH) for the determination of the post-proline cleaving enzyme (EC 3.4.21.-) were reported. Maximal activity of the enzyme purified from lamb kidney for the new substrate was observed at pH 7.0. This substrate showed a higher affinity (Km = 0.02 mM) for the enzyme than the proline containing substrates studied previously and allowed the detection of 10-50 ng post-proline cleaving enzyme activity per ml sample after a 1 min incubation period. Distribution of post-proline cleaving enzyme and other proline specific peptidases in rat tissues was studied using Z-Gly-Pro-MeCouNH and other proline-containing substrates. High post-proline cleaving enzyme activity was observed in testis, liver and skeletal muscle. Inhibition experiments indicated that post-proline cleaving enzyme activity was completely inactivated by 0.1 mM diisopropylphosphofluoridate and Z-Gly-Pro-chloromethylketone, as had been found in the case of the enzyme isolated from lamb kidney. Activity in human body fluids was also tested for levels of post-proline cleaving enzyme activity using Z-Gly-Pro-MeCouNH and semen was found to show the highest cleaving activity.     

Delineation of a Particulate Thyrotropin-Releasing Hormone-Degrading Enzyme in Rat Brain by the Use of Specific Inhibitors of Prolyl Endopeptidase and Pyroglutamyl Peptide Hydrolase

The degradation of thyrotropin-releasing hormone in rat brain homogenates was studied in the presence of N-benzyloxycarbonyl-prolyl-prolinal and pyroglutamyl diazomethyl ketone, specific and potent active-site-directed inhibitors of prolyl endopeptidase and pyroglutamyl peptide hydrolase, respectively. Substantial TRH degradation was observed, suggesting the presence of another thyrotropin-releasing hormone-degrading enzyme(s). Reports of a thyrotropin-releasing hormone-degrading enzyme with narrow specificity that cleaves the pGlu-His bond of this tripeptide led us to develop a coupled assay using pGlu-His-Pro-2NA as the substrate to measure this activity. Cleavage of the pGlu-His bond of this substrate under conditions in which pyroglutamyl peptide hydrolase is not expressed occurred in the particulate fraction of a rat brain homogenate. This particulate pyroglutamyl-peptide cleaving enzyme was not inhibited by pyroglutamyl diazomethyl ketone but was inhibited by metal chelators such as EDTA and o-phenanthroline. The particulate pyroglutamyl-peptide cleaving enzyme was found predominantly in the brain. Activity in brain regions varied widely with highest levels present in cortex and hippocampus and very low levels in pituitary. The data suggest that degradation of thyrotropin-releasing hormone by the particulate fraction of a brain homogenate is catalyzed mainly by an enzyme that cleaves the pGlu-His bond of thyrotropin-releasing hormone but is distinct from pyroglutamyl peptide hydrolase.     

Synthesis and inhibitory activity of acyl-peptidyl-pyrrolidine derivatives toward post-proline cleaving enzyme; a study of subsite specificity.

Several pyrrolidine derivatives have been synthesized and examined for their inhibitory activity on post-proline cleaving enzymes from Flavobacterium meningosepticum and bovine brain. Almost all the compounds tested in this study inhibited the activity of both enzymes at low IC50 values (from nM to microM) but a specificity difference was observed with alkylacyl-peptidyl-pyrrolidine derivatives which strongly inhibited only the bacterial enzyme. The most effective inhibitors have a proline residue on their P2 sites and a substituted or unsubstituted phenoxybutyryl moiety on their P3 sites. Thus phenoxybutyryl-prolyl-pyrrolidine is the most effective partial structure of the inhibitors. The best inhibitors found were: 4-(4-benzylphenoxy)butyryl-prolyl-pyrrolidine for bacterial enzyme (IC50 1.4 nM) and 4-phenylbutyryl-thioprolyl-pyrrolidine for bovine brain enzyme (IC50 67 nM). In the passive avoidance test, using amnesic rats experimentally induced with scopolamine, the pyrrolidine derivatives which had potent inhibitory activity toward post-proline cleaving enzymes also showed strong anti-amnesic activities at doses of 1-5 mg/kg, i.p.     

Synthesis and inhibitory activity of acyl-peptidyl-prolinalderivatives toward post-proline cleaving enzyme as nootropic agents

Several prolinal derivatives were synthesized and examined for their inhibitory activity on post-proline cleaving enzymes from Flavobacterium meningosepticum and bovine brain and their possible properties as nootropic agents. Almost all the compounds tested inhibited the activity of both enzymes at low IC50 values of the order of nM, but a specificity difference was observed with alkylacyl-prolinal derivatives which strongly inhibited only the bacterial enzyme. Prolyl-prolinal derivatives were the most effective inhibitors for both enzymes. In the passive avoidance test using amnesic rats experimentally induced with scopolamine, the prolinal derivatives that have potent inhibitory activity toward post-proline cleaving enzymes showed also strong anti-amnesic activities at dose of 10-1000 micrograms/kg, i.p. Some of the compounds showed a bell-shape dose dependency. These results suggest that the post-proline cleaving enzymes play an important role in the regulation of learning and memory consolidation in the brain and inhibitors of these enzymes are suggested as possible candidates for nootropic agents, particularly for an anti-amnesic drug.     

CYCLIC NUCLEOTIDE PHOSPHODIESTERASE OF HUMAN CEREBROSPINAL FLUID

Abstract— Cyclic 3',5'-AMP (cAMP) and cyclic 3',5'–GMP (cGMP) phosphodiesterase activities were found in human cerebrospinal fluid (CSF) using low substrate concentration (0.4μM). More rapid hydrolysis of cGMP than that of cAMP was observed in human CSF. However, cGMP hydrolytic activity of CSF was very much lower (0.3 pmol/min/ml CSF) than that of human cerebral cortex (33.7 nmol/min/g wet cortex). The pH optimum was found to be 8.0 (cGMP phosphodiesterase) and 7.5 (cAMP phosphodiesterase). The maximum stimulation of both cAMP and cGMP phosphodiesterase was achieved at 4 mM-MgCl₂. Cyclic AMP had relatively little effect on the hydrolysis of cGMP in CSF and the cortex, while cGMP inhibited hydrolysis of cAMP in both tissues. Snake venom was found to stimulate cAMP and cGMP phosphodiesterase activity of CSF, by 60% and 110% respectively. This stimulation by snake venom was also observed in the cortex phosphodiesterase, but was not observed in human plasma or thyroid phosphodiesterase. When CSF was applied to Sepharose 6B column, cGMP phosphodiesterase was separated into three different molecular forms. A plot of activity against substrate concentration using peak I (largest molecular size) revealed a high affinity ( K _m= 2.6μM) and a low affinity ( K _m= 100μM) for cAMP suggesting the existence of at least two molecular forms of the enzyme. On the other hand, using a cGMP as substrate the only one K _m value (1.90 μm) was obtained. These K _m values of CSF enzymes described above were close to those obtained from human cerebral cortex preparations. The enzyme under peak I corresponded to the cortex enzyme when judged from its molecular size and stimulation by snake venom. It seems likely from our results that at least a part of CSF phosphodiesterase originates from the central nervous system.     

Dopamine D1-stimulated adenylyl cyclase activity in cerebral cortex of autopsied human brain.

Although the cerebral cortical dopamine D(1) receptor is considered to play a role in normal and abnormal brain function, little information is available on its characteristics in human brain. We compared dopamine-stimulated adenylyl cyclase (AC) activity in homogenates of cerebral cortex (frontal, temporal, parietal, occipital and cingulate cortex) of autopsied brain of neurologically normal subjects to that in striatum. Cerebral cortical AC activity was modestly and dose-dependently stimulated by dopamine (maximal 20-30%) with low microM EC50s and such stimulation was inhibited by the selective dopamine D1 receptor antagonist SCH23390. The magnitude of the maximal stimulation by dopamine was similar in autopsied and biopsied cerebral cortex. The extent of maximal stimulation was similar to that in dopamine-rich striatum (caudate, putamen and nucleus accumbens), despite much lower density of dopamine D1 receptors in cerebral cortex vs. striatum. The EC50 for dopamine stimulation in cerebral cortex (approximately 1 microM) was lower than that for caudate and putamen (approximately 3 microM). No detectable dopamine stimulation was observed in cerebellar cortex, thalamus or hippocampus. Dopamine stimulation in both cerebral cortex and striatum was independent of calcium activation. We conclude that dopamine stimulated AC can be measured in cerebral cortex of human brain allowing for the possibility that this process can be examined in human brain disorders in which dopaminergic abnormalities are suspected.     

Immunohistochemical detection of betaine-homocysteine S-methyltransferase in human, pig, and rat liver and kidney

Betaine-homocysteine S-methyltransferase (BHMT) has been shown to be expressed at high levels in the livers of all vertebrate species tested. It has also been shown to be abundant in primate and pig kidney but notably very low in rat kidney and essentially absent from the other major organs of monogastric animals. We recently showed by enzyme activity and Western analysis that pig kidney BHMT was only expressed in the cortex and was absent from the medulla. Using immunohistochemical detection, we report here that in human, pig, and rat kidney, BHMT is expressed in the proximal tubules of the cortex. Immunohistochemical staining for BHMT in human, pig, and rat liver indicate high expression in hepatocytes. The staining patterns are consistent with cytosolic expression in both organs.     

Distribution and activity of pyridoxal kinase in human brain during ontogenesis]

The activity of pyridoxal kinase was sharply increased in whole brain tissue of human, embryos and fetuses within 6-11 weeks of development. In brain stem the maximal values of the enzyme activity was observed at early stages of prenatal development of fetuses. The activity of pyridoxal kinase was increased in cerebral cortex and in the limbic system up to complete maturation of fetuses. It correlated with the fetus age within 14-40 weeks of development as calculated per 1 g of tissue wight or 1 mg of protein. The enzyme is distributed evenly in brain of newborns, babies and adult people. Its activity in grey cortex substance is higher, than in white one. There are 2-10-fold individual fluctuations of pyridoxal kinase activity in brain of people without CNS pathology. In newborns, having prolonged hypoxy at prenatal period, the enzyme activity was on the average by 70-80% lower at different brain parts than in newborns which had no primary asphyxia. A low pyridoxal kinase activity (not more than 1-5% as compared with its normal level) was observed in different brain parts of a child affected by focal gliosis and epilepsy.     

Inhibition of Calpains by Calmidazolium and Calpastatin

Abstract

Several prolinal derivatives were synthesized and examined for their inhibitory activity on post-proline cleaving enzymes from Flavobacterium meningosepticum and bovine brain and their possible properties as nootropic agents. Almost all the compounds tested inhibited the activity of both enzymes at low IC₅₀ values of the order of nM, but a specificity difference was observed with alkylacyl-prolinal derivatives which strongly inhibited only the bacterial enzyme. Prolyl-prolinal derivatives were the most effective inhibitors for both enzymes. In the passive avoidance test using amnesic rats experimentally induced with scopolamine, the prolinal derivatives that have potent inhibitory activity toward post-proline cleaving enzymes showed also strong anti-amnesic activities at doses of 10 ~ 1000μg/kg, i.p. Some of the compounds showed a bell-shape dose dependency. These results suggest that the post-proline cleaving enzymes play an important role in the regulation of learning and memory consolidation in the brain and inhibitors of these enzymes are suggested as possible candidates for nootropic agents, particularly for an anti-amnesic drug.     

Insulin and glucagon degradation by the kidney. I. Subcellular distribution under different assay condition.

Insulin and glucagon degradation by rat kidney homogenates and subcellular fractions was examined under a variety of conditions including high and low substrate concentrations, at pH 4 and pH 7, with and without glutathione. At high insulin concentration (4.1 - 10(-5) M) insulin degradation by the homogenate was greatest at pH 4 but at low insulin concentration (1 - 10(-10) M) insulin degradation was greatest at pH 7. At either high or low glucagon concentration glucagon degradation by the homogenate was greatest at pH 7. Glutathione at pH 7 stimulated insulin degradation at high insulin concentrations and inhibited insulin degradation at low concentrations; Glucagon degradation at pH 7 was inhibited at both high and low concentrations of glucagon by glutathionemseparation of kidney into cortex and medulla prior to homogenation produced a pattern of insulin and glucagon degradation identical to the whole homogenate but glucagon degradation by the medulla was greater than by the cortex. Examination of degradation by subcellular fractions revealed that at high concentration at neutral pH most insulin was degraded by the 100 000 X g pellet but at low insulin concentrations over 90% of the activity was in the 100 000 X g supernatant; At pH 7, at both high and low concentrations, most glucagon-degrading activity was in the 100 000 X g pellet, although the cytosol also had activity; At pH 4 most degradation occurred in the lysosomal fractions. Separation into cortex and medulla again showed similar distribution of activity as the whole gland with the medulla having more glucagon-degrading activity than the cortex. With low insulin concentrations the cortex 100 000 X g supernatant had higher relative specific activities than the medulla supernatant. Examination of recoveries of enzyme activity revealed that the subcellular fractions consistently had markedly less insulin-degrading activity than the original homogenate. This loss of activity was only discernible when insulin degradation was performed at pH 7 at low substrate concentrations. Comparable losses of glucagon-degrading activity were not seen.     

Separation and characterization of two carnosine-splitting cytosolic dipeptidases from hog kidney (carnosinase and non-specific dipeptidase)

High performance anion-exchange chromatography was used to separate two carnosine-hydrolysing dipeptidases from hog kidney. Both enzymes (peaks I and II) were cytosolic and were activated and stabilized by Mn2+ and dithiothreitol. Peak I had a narrow specificity when assayed without added metal ions, but a broad specificity in the presence of Mn2+ or Co2+. Peak II was inactive unless both Mn2+ and dithiothreitol were present. Bestatin and leucine inhibited peak II, but not peak I. Peak I had a Km of 0.4 mM carnosine, a pI of 5.5 and a Mr of 57,000. Peak II had a Km of 5 mM carnosine, a pI of 5.0 and a Mr of 70,000. Hog and rat brain and liver carnosinase activity was completely inhibited by bestatin, indicating that these organs contained peak II, with little or no peak I enzyme. Hog kidney peak I contained the classical carnosinase of Hanson and Smith, who first described this enzyme. It also contained activity against homocarnosine ("homocarnosinase") and showed "manganese-independent carnosinase" activity. These three activities could not be separated using 8 different chromatographic procedures; it was concluded that they are attributable to one enzyme. It is recommended that the name carnosinase be retained for this enzyme and the names "homocarnosinase" and "manganese-independent carnosinase" be withdrawn. The properties of hog kidney peak II closely resembled those of human tissue carnosinase (also known as prolinase, a non-specific dipeptidase), mouse "manganese-dependent carnosinase" and a rat brain enzyme termed "beta-Ala-Arg hydrolase". Since these terms appear to represent closely related enzymes with broad specificity, the recommended name for each is "non-specific cytosolic dipeptidase".     

Effects of digoxin and gitoxin on the enzymatic activity and kinetic parameters of Na+/K+-ATPase

Inhibition of Na+/K+-ATPase activity from human erythrocyte membranes and commercial porcine cerebral cortex by in vitro single and simultaneous exposure to digoxin and gitoxin was investigated to elucidate the difference in the mechanism of the enzyme inhibition by structurally different cardiac glycosides. The drugs exerted a biphasic dose-dependent inhibitory effect on the enzyme activity in both tissues, supporting the existence of two sensitive Na+/K+-ATPase isoforms. The IC50 values for the low and high affinity isoforms were calculated from the inhibition curves using mathematical analysis. The Hill coefficient (n) fulfilled the relationship 1 < n < 3, suggesting cooperative binding of inhibitors to the enzyme. Kinetic analysis showed that digoxin and gitoxin inhibited Na+/K+-ATPase by reducing the maximum enzymatic velocity (Vmax) and Km, implying an uncompetitive mode of interaction. Both the isoforms were always more sensitive to gitoxin. The erythrocyte enzyme was more sensitive to the inhibitors in the range of low concentrations but the commercial cerebral cortex enzyme exerted a higher sensitivity in high inhibitors affinity concentration range. By simultaneous exposure of the enzyme to digoxin and gitoxin in combinations a synergistic effect was achieved by low inhibitor concentrations. An antagonistic effect was obtained with erythrocyte membrane enzyme at high inhibitors concentration.     

The processing of Alzheimer A4/beta-amyloid protein precursor: identification of a human brain metallopeptidase which cleaves -Lys-Leu- in a model peptide

A search for human brain peptidases with the specificity to cleave the 695 residue A4/beta amyloid precursor protein within the -Gln-Lys-Leu- (611-613) sequence was carried out using carbobenzoxy-Gln-Lys-Leu-p-nitroanilide as substrate. A metalloendopeptidase was identified in the soluble fraction of post mortem human cerebral cortex which cleaves the substrate at the Lys-Leu bond. The enzyme was partially purified by anion exchange and size exclusion chromatography; it has a Mr of approximately 105-120 kda, is inhibited by EDTA but can be reactivated by Mn++ ions, and has maximum activity between pH 6.8 and 8.     

Changes in acetylcholinesterase and butyrylcholinesterase in Alzheimer's disease resemble embryonic development--a study of molecular forms.

The pattern of molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BChE, EC 3.1.1.8) separated by density gradient centrifugation was investigated in the brain and cerebrospinal fluid in Alzheimer's disease (AD), in human embryonic brain and in rat brain after experimental cholinergic deafferentation of the cerebral cortex. While a selective loss of the AChE G4 form was a rather constant finding in AD, a small but significant increase of G1 for both AChE and BChE was found in the most severely affected cases. Both in normal human brain and in AD a significant relationship could be established between the AChE G4/G1 ratio in different brain regions and the activity of choline acetyltransferase (ChAT). A similar decrease of the AChE G4 form as observed in AD can be induced in rat by experimental cholinergic deafferentation of the cerebral cortex. The increase in G1 of both AChE and BChE in different brain regions in AD is quantitatively related to the local density of neuritic plaques which are histochemically reactive for both enzymes. In human embryonic brain, a high abundance of G1 and a low G4/G1 ratio for both AChE and BChE was found resembling the pattern observed in AD. Furthermore, both in embryonic brain and in AD AChE shows no substrate inhibition which is a constant feature of the enzyme in the adult human brain. It is, therefore, concluded that the degeneration of the cholinergic cortical afferentation in AD as reflected by a decrease of AChE G4 is accompanied by the process of a neuritic sprouting response involved in plaque formation which is probably associated with the expression of a developmental form of the enzyme.     

Differential Changes in Superoxide Dismutase Activity in Brain and Liver of Old Rats and Mice

Superoxide dismutase (SOD) activity was measured in the brain and liver of 24–26- and 3-month-old rats. No significant age-related differences in Cu/Zn-SOD activity were found in any of the tissues studied. A small but significant increase in total SOD activity was observed in the whole brain (10-20%), cerebral cortex (11%), and hypothalamus (18%) of old rats, whereas a much more important increase in Mn-SOD activity was found in the whole brain (48%), cerebral cortex (70%), striatum (60%), and hypothalamus (30%). The increase of Mn-SOD activity in the brain of old rats suggests the enzyme may play an important role in the process of aging. Mn-SOD is found only in the mitochondrion, which could be an important site of oxygen free radical production, and a significant increase in the enzyme activity was also found in the lung of hypoxic rats. A significant decrease in total SOD and Mn-SOD activity was observed in the liver of old rats. Preliminary experiments in 23–24-month-old mice similarly showed an increase and a decrease in total SOD and Mn-SOD activity, respectively, in the whole brain and liver. These results suggest that the regulatory mechanisms of Mn-SOD in the brain and liver vary differentially with age.     

Purification and properties of AMP-deaminase from human kidney.

AMP-deaminase from human kidney (cortex and medulla) was purified and the physicochemical properties were characterized. The enzyme from both portions of the kidney exhibited identical kinetics and regulatory properties. At optimal pH (6.6), the AMP-deaminase studied exhibited a distinctly sigmoidal substrate saturation kinetics, with the half-saturation parameter (S0.5) as high as 10 mM. ATP at 1 mM strongly activated the enzyme, decreasing S0.5 nearly 10-fold. The activating effect of ADP was less strong. Orthophosphate inhibited the enzyme, but the inhibition observed was weak (Ki approximately 16 mM) and had a pure competitive character. At pH 7.2, physiological for the kidney cortex, orthophosphate inhibition became even weaker and became partially competitive. Variations in the adenylate energy charge had potent effects on the activity of AMP-deaminase, depending on the size of the total adenine nucleotide pool examined. The results of gel filtration and SDS-PAGE indicated that human kidney AMP-deaminase is an oligomeric enzyme composed of four, probably identical, subunits weighing about 37 kDa each.     

Influence of thyroid hormone deficiency on the citrate synthase activity in rat brain regions during early postnatal development

The developmental pattern of citrate synthase activity has been studied in the liver and several brain areas of hypothyroid rats during the 4 first weeks of life. While citrate synthase activity in the liver showed a rise during the 2 first weeks of life, different patterns of enzyme activity were found in the brain regions of euthyroid animals. Citrate synthase activity increased in the cerebellum, decreased in the cerebral cortex and did not change significantly in the brain stem during the period studied. In the liver and brain areas, too, a decrease in citrate synthase activity was observed during hypothyroidism. From the 2nd week of birth, the citrate synthase activity in the brain but not in the liver was found to have recovered. The newly elevated citrate synthase activity coincided with a slight increase in thyroid hormone serum levels.     

Identification with a Monoclonal Antibody of a Phylogenetically Conserved Brain-Specific Determinant on a 130,000 Molecular Weight Glycoprotein of Human Brain

Human brain glycoproteins depleted of Thy-1 antigen were used to immunise Balb/c mice for monoclonal antibody production. The F3-87-8 antibody described in this paper interacts with a determinant present in large amounts on all human brain subregions studied (cerebral cortical grey matter, white matter, caudate, thalamus, dentate nucleus, putamen, cerebellar cortex) but absent from all other tissues examined (liver, heart, kidney, spleen, thymus, lymph node, erythrocyte, adrenal gland, and peripheral nerve). The determinant is conserved in mammalian evolution, as the brains of the rat and dog have amounts equal to that found in human brain. Balb/c mouse brain has approximately one-third as much antigen activity as these other mammalian brains, whereas brains of the frog and chicken have no detectable antigenic activity. Developmental studies showed that 16-week human foetal brain and neonatal dog brain had little or no antigen activity, indicating a dramatic increase in the amount of the determinant with brain maturation. Biochemical studies showed that the F3-87-8-bearing molecule was a major sialoglycoprotein of human brain with an apparent molecular weight of 130,000. It was shown by immunofluorescence to be particularly localised in what appeared to be fibre tracts in the thalamus and basal ganglia, and in the dentate nucleus, although all regions including grey matter were stained.