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P Nef

Publications and source records attributed to P Nef.

29 records · Page 2Linked to original sources
PubMed1991

Odorant signal termination by olfactory UDP glucuronosyl transferase.

The onset of olfactory transduction has been extensively studied, but considerably less is known about the molecular basis of olfactory signal termination. It has been suggested that the highly active cytochrome P450 monooxygenases of olfactory neuroepithelium are termination enzymes, a notion supported by the identification and molecular cloning of olfactory-specific cytochrome P450s (refs. 13-16). But as reactions catalysed by cytochrome P450 (refs 17, 18) often do not significantly alter volatility, lipophilicity or odour properties, cytochrome P450 may not be solely responsible for olfactory signal termination. In liver and other tissues, drug hydroxylation by cytochrome P450 is frequently followed by phase II biotransformation, for example by UDP glucuronosyl transferase (UGT), resulting in a major change of solubility and chemical properties. We report here the molecular cloning and expression of an olfactory-specific UGT. The olfactory enzyme, but not the one in liver microsomes, shows preference for odorants over standard UGT substrates. Furthermore, glucuronic acid conjugation abolishes the ability of odorants to stimulate olfactory adenylyl cyclase. This, together with the known broad spectrum of drug-detoxification enzymes, supports a role for olfactory UGT in terminating diverse odorant signals.

Amino Acid Sequence↗
PubMed1990

Olfactory-specific cytochrome P-450 (P-450olf1; IIG1). Gene structure and developmental regulation.

The olfactory neuroepithelium is the principal site of interaction for airborne molecules, mainly odorants, in the organism. The presence of an active cytochrome P-450-dependent oxidative metabolism in this tissue has not yet been studied as well as the hepatic cytochrome P-450-dependent oxidations. In this report, we describe cytochrome P-450olf1 (IIG1), a P-450 gene expressed at high levels uniquely in the olfactory epithelium. By Southern analysis and genomic DNA cloning, we demonstrate that a single copy of the P-450olf1 gene is present in the rat genome and contains 9 exons. We conclude that rat P-450IIG1 is a single gene subfamily. P-450olf1 gene expression was activated after birth in both male and female Sprague-Dawley rats and remained active in adult olfactory epithelium. A first maximum level of expression was reached around postnatal day 21. The coincidence between the temporal gene activation of P-450olf1 and the postnatal increase in the sensitivity of olfactory response to odorants is consistent with a potential role of this enzyme in olfactory function.

Aging↗
PubMed1989

Olfactory-specific cytochrome P-450. cDNA cloning of a novel neuroepithelial enzyme possibly involved in chemoreception.

We isolated cDNA clones for cytochrome P-450 genes expressed in the olfactory neuroepithelium by screening a corresponding rat cDNA library. Sequence analysis and RNA blot hybridization revealed a new cytochrome P-450, designated cytochrome P-450olf1, which is the first reported cytochrome P-450 mRNA uniquely expressed in the chemosensory organ. Cytochrome P-450olf1 shows intermediate level of sequence similarity (38-53% identity) to several liver cytochrome P-450 enzymes, suggesting that it belongs to the cytochrome P-450II family, but defines a new subfamily (cytochrome P-450IIG) within it. Cytochrome P-450II enzymes are known to process diverse organic compounds, including odorants. This, together with the specificity of cytochrome P-450olf1 to the sensory neuroepithelium, may indicate a role for this protein in olfactory reception.

Amino Acid Sequence↗
PubMed1988

Genes expressed in the brain define three distinct neuronal nicotinic acetylcholine receptors.

Four genes encode the related protein subunits that assemble to form the nicotinic acetylcholine receptor (nAChR) at the motor endplate of vertebrates. We have isolated from the chicken genome four additional members of the same gene family whose protein products, termed alpha 2, alpha 3, alpha 4 and n alpha (non-alpha) probably define three distinct neuronal nAChR subtypes. The neuronal nAChR genes have identical structures consisting of six protein-coding exons and specify proteins that are best aligned with the chicken endplate alpha subunit, whose gene we have also characterized. mRNA transcripts encoding alpha 4 and n alpha are abundant in embryonic and in adult avian brain, whereas alpha 2 and alpha 3 transcripts are much scarcer. The same set of neuronal genes probably exists in all vertebrates since their counterparts have also been identified in the rat genome.

Age Factors↗
PubMed1988

Electrophysiology of a chick neuronal nicotinic acetylcholine receptor expressed in Xenopus oocytes after cDNA injection.

Brain nicotinic acetylcholine receptors (nAChRs) are made up of protein subunits that differ from those constituting muscle nAChRs. To characterize the physiological properties of one class of avian brain nicotinic receptor, we injected the nuclei of Xenopus oocytes with full-length cDNAs for the ligand binding (alpha 4) and structural (n alpha) subunits. Injected oocytes had large ACh-induced currents in the microampere range that were insensitive to alpha-bungarotoxin, as expected for neuronal nAChRs. We found that these brain nAChRs incorporate at least two alpha 4 subunits and that their functional properties differ from muscle nAChRs in at least two respects: the elementary conductance is considerably smaller (20 pS), and channels in outside out patches stop functioning within a few minutes.

Animals↗
PubMed1984

Study in pig coronary smooth muscle cell subcellular fractions of the activity of various enzymes involved in lipid metabolism and of the beta-receptor adenylate cyclase couple.

Pig coronary smooth muscle cells contain a highly active fatty acid beta-oxidation system as well as significant activities of other enzymes involved in lipid metabolism, i.e. palmitoyl-CoA synthetase, glycerophosphate acyl transferase, acetyl-CoA carboxylase and fatty acid synthetase. Purified plasma membranes of pig coronary smooth muscle cells contain stereospecific (-)-[3H]dihydroalprenolol binding sites of high affinity (Kd = 5.4 nM) and characteristic of the beta 1 subtype. They also contain an adenylate cyclase activity which is stimulated by 5'-guanylyl-imidodiphosphate (Gpp(NH)p) and, to a lesser degree, by (-)-isoproterenol.

Adenylyl Cyclases↗
PubMed1984

Structure linkage, and sequence of the two genes encoding the delta and gamma subunits of the nicotinic acetylcholine receptor.

We have cloned and sequenced a fragment of the chicken genome approximately 9 kilobases in length that comprises the genes encoding the delta and gamma subunits of the nicotinic acetylcholine receptor. The two genes are homologous and have identical structures: both consist of 12 exons, some of which precisely correspond to predicted structural domains of the receptor subunits. The delta and gamma subunit genes are encoded by the same DNA strand and are very closely linked, there being only 740 base pairs between the last codon of delta and the initiator codon of gamma. Blot analysis demonstrates that the genes we describe are unique in the genome. Comparison of the predicted protein sequence for the corresponding subunits of chicken and of the elasmobranch Torpedo reveals a high degree of conservation in some but not all of the protein domains.

Amino Acid Sequence↗
PubMedDate not supplied

Identification of neuronal calcium sensor (NCS-1) possibly involved in the regulation of receptor phosphorylation.

Persistent stimulation of G protein-coupled receptors by agonists leads rapidly to reduced responses, a phenomenon described as desensitization. It involves primarily the phosphorylation of receptor sites by specific kinases of the G protein-coupled receptor kinase (GRK) family. The beta-adrenergic receptor kinase 1 (GRK2) desensitizes agonist-activated beta2-adrenergic receptors, whereas rhodopsin kinase (GRK1) phosphorylates and inactivates photon-activated rhodopsin. Little is known about the role of calcium in desensitization. Here we report the characterization of a novel neuronal calcium sensor (NCS) named NCS-1 possibly involved in the regulation of receptor phosphorylation. NCS-1 is a new member of the EF-hand superfamily, which includes calmodulin, troponin C, parvalbumin, and recoverins. By Northern analysis and in situ hybridization, we discovered that NCS-1 is specifically expressed in the central and peripheral nervous systems. Chick NCS-1 has 72% of amino acid identity with Drosophila frequenin, a protein found in the nervous system and at the motor nerve terminals of neuromuscular junctions. By analogy with the reported function for two other members of the NCS family, we discuss whether G protein-coupled receptors or GRKs are the targets of neuronal calcium sensors.

Amino Acid Sequence↗