摘要:

Abstract:In this article, the enzymes of brain and associated tissues that can degrade thyrotropin‐releasing hormone (TRH) and luteinising hormone‐releasing hormone (LH‐RH) are reviewed. As both TRH and LH‐RH are considered to act as neurotransmitters or neuromodulators in the CNS, attention is paid to the subcellular location of the enzymes described and how their topographies and substrate specificities fit them to playing roles as inactivating agents for TRH and LH‐RH or as regulators of intracellular concentrations of TRH and LH‐RH. Consideration is also given to enzymes involved in biotransformation of TRH to secondary metabolites that exhibit biological activity and to enzymes involved in the metabolism of secondary

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13276.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13277.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Many similarities of both the inheritance pattern and the neuropathology can be observed between olivopontocerebellar atrophies, or so‐called multiple system atrophies (MSAs), and murine cerebellar mutations like Purkinje cell degeneration, nervous, staggerer, weaver, and reeler. Our study aimed to test whether the glutamate dehydrogenase (GDH) deficiency observed in some MSA patients could be found also in any of the murine mutants. GDH activity was assayed in several organs of these mutants, and no general deficiency was detected. By contrast, the level was found to be elevated in the cerebellum. The GDH gene was localized on mouse chromosome 14 and does not map close to any known neurological mutation in the mouse. We conclude, for the moment, that none of these cerebellar mutant mice can be considered as an animal model for GDH‐deficient

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13278.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:In AtT‐20 cells somatostatin inhibits the secretion of adrenocorticotropic hormone (ACTH) through the activation of GTP binding proteins (G proteins) linked to second messengers such as calcium and cyclic AMP (cAMP). Recently, it has been proposed that there may be G proteins that regulate directly the exocytotic machinery. We have investigated whether somatostatin could inhibit secretion at a step distal to second messengers through a GTP binding protein. For these studies two experimental paradigms were used: (1) intact cells stimulated by calcium ionophores and (2) digitonin‐permeabilized cells exposed to buffers of increasing Ca2+concentrations. Somatostatin inhibited by 70% the ACTH release caused by the calcium ionophore ionomycin without modifying the ionophore‐induced elevation in cytosolic [Ca2+]. This effect was cAMP independent because (1) it was observed in the presence of high concentrations of membrane‐permeant cAMP analogues, and (2) it was not accompanied by a change in cAMP levels. The effect was also independent of the levels of activators of protein kinase C because it could be produced in the presence of high concentrations of phorbol esters. The action of somatostatin was prevented by pertussis toxin. In digitonin‐permeabilized AtT‐20 cells somatostatin inhibited release induced by calcium buffers in a GTP‐dependent manner. These two observations indicate the involvement of a G protein. It is proposed that a G protein coupled to somatostatin receptors inhibits the intracellular machinery of secretion at a step distal to second messengers, perhaps at the ex

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13279.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The guanine nucleotide analogue, 5′‐p‐fluorosul‐phonylbenzoyl guanosine (FSBG), can react covalently with GTP‐binding proteins (G proteins). In rat brain membranes, FSBG causes a time‐dependent loss of β,γ‐imido[8‐3H]guanosine 5′‐triphosphate binding sites. Using 1 mMFSBG, the guanyl nucleotide modulation of opioid agonist binding is abolished, whereas the guanyl nucleotide sensitivity of neurotensin binding is retained. The action of FSBG can be prevented by the presence of opioid agonists, but not the antagonist naloxone. Iodoacetamide treatment of membranes in the presence of agonist, but not antagonist, can attenuate the action of FSBG in blocking guanyl nucleotide modulation of opioid agonist binding. These results suggest that FSBG covalently modifies essential thiol groups, whose exposure to the reagent is modified by agonist occupancy of the receptor, on a species of G protein linked to opioid receptors, but not on a species of G protein linked to neurotensin receptors. Thus, FSBG may have selectivity for the forms of Gior Go, proteins associated

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13280.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The 50‐kilodalton (kDa) assembly polypeptide of bovine brain clathrin coated vesicles (CCVs) is phosphorylated in a cyclic nucleotide‐ and Ca2+‐independent manner and is dephosphorylated by a Mg2+‐ATP‐dependent CCV phosphatase. This report provides evidence for modulation of the phosphorylation reaction of the 50‐kDa assembly polypeptide by phosphorylated clathrin light chain β (pLCβ). In vitro, phosphorylated LCβ inhibits phosphorylation of the 50‐kDa polypeptide in CCVs. Furthermore, incubation of previously phosphorylated 50‐kDa polypeptide in CCVs with phosphorylated LCβ results in a rapid dephosphorylation of the 50‐kDa assembly polypeptide. Both phenomena are time and concentration dependent. Monoclonal antibodies to LCβ prevent the modulatory effect of phosphorylated LCβ on the 50‐kDa assembly polypeptide phosphorylation in CCVs. The results obtained indicate for the first time, to our knowledge, that phosphorylated LCβ has a modulatory role in CCVs. The data also suggest that phosphorylated LCβ promotes activation of a

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13281.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Most anti‐nicotinic acetylcholine receptor (AChR) antibodies in myasthenia gravis are directed against an immunodominant epitope or epitopes [main immunogenic region (MIR)] on the AChR α‐subunit. Thirty‐two synthetic peptides, corresponding to the completeTorpedoα‐subunit sequence and to a segment of human muscle α‐subunit, were used to map the epitopes for 11 monoclonal antibodies (mAbs) directed against the Torpedo and/or the human MIR and for a panel of anti‐AChR mAbs directed against epitopes on the α‐subunit other than the MIR. A main constituent loop of the MIR was localized within residues α67‐76. Residues 70 and 75, which are different in theTorpedoand human α‐subunits, seem to be crucial in determining the binding profile for several mAbs whose binding to the peptides correlated very well with their binding pattern to nativeTorpedoand human AChRs. This strongly supports the identification of the peptide loop α67‐76 as the actual location of the MIR on the intact AChR molecule. Residues 75 and 76 were necessary for binding of some mAbs and irrelevant for others, in agreement with earlier suggestions that the MIR comprises overlapping epitopes. Structural predictions for the sequence segment α67‐76 indicate that this segment has a relatively high segmental mobility and a very strong turning potential centered around residues 68‐71. The most stable structure predicted for this segment, in both theTorpedoand human α‐subunits, is a hairpin loop, whose apex is a type I β‐turn and whose arms are β‐strands. This loop is highly hydrophilic, and its apex is negatively charged. All these structural properties have been proposed as characteristic of antibody binding sites. We also localized the epitopes for mAbs against non‐MIR regions. Among these, the epitope for a monoclonal antibody (mAb 13) that noncompetitively inhibits channel funct

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13282.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:Three annexins‐p68, endonexin, and p32‐have been isolated from porcine brain using their calcium‐dependent affinity for membranes. Large amounts (20‐50 mg/kg of tissue) of p68 and p32 can be isolated from cerebrum and cerebellum. The p68 is present as up to 0.3% of total porcine brain protein. The p68 and p32 from porcine brain bind to phosphatidic acid (half‐maximal binding at 6 and 34 μM free calcium, respectively) and to phosphatidylserine (8 and 34 μM, respectively). They do not bind to phosphatidylcholine at calcium concentrations up to 1 mM. Two other major proteins (Mr180,000 and Mr76,000) were isolated with the annexins in a calcium‐dependent manner but do not bind to phospholipids. The 180‐kilodalton protein is the heavy chain of clathrin. From immunohistochemical studies, p68 is strongly associated with the plasma membranes of Purkinje cell bodies and dendrites in porcine cerebellum. It is also an intracellular component of Purkinje cells localized to perinuclear structures. Staining of axons in the white matter and granule cell layer was also seen. In contrast, p32 is completely absent from Purkinje cells and their dendrites; it is predominantly located in the molecular layer and in white matter of the cerebellar folds. The distribution of p32 may be consistent with a predominantly gli

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13283.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The effects of the organophosphate acetylcholinesterase (AChE) inhibitor soman (31.2 μg/kg s.c.) on guinea‐pig brain AChE, transmitter, and metabolite levels were investigated. Concentrations of acetylcholine (ACh) and choline (Ch), noradrenaline (NA), dopamine (DA), 5‐hydroxytryp‐tamine (5‐HT), and their metabolites, and six putative amino acid transmitters were determined concurrently in six brain regions. The brain AChE activity was maximally inhibited by 90%. The ACh content was elevated in most brain areas by 15 min, remaining at this level throughout the study. This increase reached statistical significance in the cortex, hippocampus, and striatum. The Ch level was significantly elevated in most areas by 60‐120 min. In all regions, levels of NA were reduced, and levels of DA were maintained, but those of its metabolites increased. 5‐HT levels were unchanged, but those of its metabolites showed a small increase. Changes in levels of amino acids were restricted to those areas where ACh levels were significantly raised: Aspartate levels fell, whereas γ‐Aminobutyric acid levels rose. These findings are consistent with an initial increase in ACh content, resulting in secondary changes in DA and 5‐HT turnover and release of NA and excitatory and inhibitory amino acid transmitters. This study can be used as a basis to investigate the effect of toxic agents and their treatments on the different tr

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13284.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract:The coupling mechanism of the γ‐Aminobutyric acid (GABA)Breceptor, one of the subtypes of GABA receptors, with calcium ion channel and GTP‐binding protein was examined using a crude synaptic membrane (P2) fraction from the bovine cerebral cortex and a fraction solubilized with sodium deoxycholate. In the P2fraction, [3H]GABA binding to the GABABreceptor was increased significantly by the addition of calcium ion, and this enhancement was accentuated further by calcium ion channel blockers such as nicardipine and diltiazem. In contrast,N‐(6‐aminohexyl)‐5‐chloro‐1‐naphthalenesulfonamide (W‐7), a calmodulin antagonist, did not affect on the calcium ion‐induced enhancement of GABABreceptor binding. These results suggest that the GABABreceptor may be functionally coupled with the calcium ion channel, which exhibits an inhibitory modulation against the receptor. On the other hand, GABABreceptor binding, which was noncompetitively inhibited by guanine nucleotides such as GTP, guanosine 5′‐(3‐O‐thio)triphosphate (GTPγS), guanosine 5′‐(β,γ‐imido)triphosphate [Gpp(NH)p], and GDP, was competitively inhibited by (‐)‐baclofen. Although the affinity of (‐)‐baclo‐fen for the GABABreceptor was decreased in the presence of GTP, pretreatment of the P2fraction with islet‐activating protein (IAP) eliminated the effect of GTP. In addition, GABA and (‐)‐baclofen induced an increase of GTPase activity in the P2fraction, and this increase was also eliminated by treatment with IAP. These results suggest that the GABABreceptor may also be functionally coupled with IAP‐sensitive GTP‐binding protein. Treatment of the P2fraction with sodium deoxycholate resulted in the highest solubilization of GABABreceptor among various detergents examined. The solubilization, however, completely eliminated the stimulating effects of calcium ion and calcium ion channel blockers as well as the inhibitory effects of GTP and GTP analogues on GABABreceptor binding. Furthermore, the increase of GTPase activity induced by GABA and (‐)‐baclofen was also eliminated following the solubilization. These results suggest that functional coupling of the GABABreceptor with the calcium ion channel and GTP‐binding protein such

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1990.tb13285.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY