General

GENERAL

Structural identification of polyhydroxyalkanoic acid (PHA) containing 4-hydroxyalkanoic acids by gas chromatography-mass spectrometry (GC-MS) and its application to bacteria screening

by Lee Eun Yeol, Choi Cha Yong

Biotechnology Techniques Vol 11 (No. 3) 1997; 167-171

Abstract : The methanolysis products of polyhydroxyalkanoic acids (PHAs) containing 4-hydroxybutyric acid (4HB), 4-hydroxyvaleric acid (4HV), and 4-hydroxyhexanoic acid (4HHx), when analyzed by GC-MS, showed two major chromatographic peaks with characteristic retention times of each methyl ester of 4-hydroxyalkanoic acid and the corresponding gamma -lactone ( gamma -butyrolactone, gamma -valerolactone, gamma -caprolactone, respectively). The method and results of GC-MS could be incorporated into an efficient screening procedure for isolation of bacterial strains which could accumulate a PHA containing 4-hydroxyalkanoic acid as the principal monomer from structurally related carbon substrates.

Analogues of gamma-hydroxybutyric acid. Synthesis and binding.

by Bourguignon JJ, Schoenfelder A, Schmitt M, Wermuth CG, Hechler V, Charlier B, Maitre M

J Med Chem Vol 31(5); May 1988 ; 893-7

Abstract: Substituted 4-hydroxybutyric (GHB) or trans-4-hydroxycrotonic acids (T-HCA) and structurally related compounds were synthesized and submitted to [3H]GHB binding. Structure-activity relationships studies highlighted for [3H]GHB binding (a) the necessity of a nonlactonic, relatively extended conformation of the gamma-hydroxybutyric chain, (b) the existence of some bulk tolerance in the vicinity of the hydroxyl group, and (c) the high sensitivity toward isosteric replacements of the carboxyl or the hydroxyl groups. T-HCA has been recently identified as a naturally occurring substance in the central nervous system (CNS) and shows a better affinity than GHB. Our findings are in favor of the presence in the CNS of specific GHB binding sites, which are different from the GABA and the picrotoxin binding sites, and for which T-HCA may be an endogenous ligand.

The gamma-hydroxybutyrate signalling system in brain: organization and functional implications.

by Maitre M

Prog Neurobiol Vol 51(3); Feb 1997 ; 337-61

Abstract: gamma-Hydroxybutyrate is a metabolite of GABA which is synthesized and accumulated by neurons in brain. This substance is present in micromolar quantities in all brain regions investigated as well as in several peripheral organs. Neuronal depolarization releases gamma-hydroxybutyrate into the extracellular space in a Ca(2+)-dependent manner. Gamma-hydroxybutyrate high-affinity receptors are present only in neurons, with a restricted specific distribution in the hippocampus, cortex and dopaminergic structures of rat brain (the striatum in general, olfactory bulbs and tubercles, frontal cortex, dopaminergic nuclei A9, A10 and A12). Stimulation of these receptors with low amounts of gamma-hydroxybutyrate induces in general hyperpolarizations in dopaminergic structures with a reduction of dopamine release. However, in the hippocampus and the frontal cortex, it seems that gamma-hydroxybutyrate induces depolarization with an accumulation of cGMP and an increase in inositol phosphate turnover. Some of the electrophysiological effects of GHB are blocked by NCS-382, a gamma-hydroxybutyrate receptor antagonist while some others are strongly attenuated by GABAB receptors antagonists. Gamma-hydroxybutyrate penetrates freely into the brain when administered intravenously or intraperitoneally. This is a unique situation for a molecule with signalling properties in the brain. Thus, the gamma-hydroxybutyrate concentration in brain easily can be increased more than 100 times. Under these conditions, gamma-hydroxybutyrate receptors are saturated and probably desensitized and down-regulated. It is unlikely that GABAB receptors could be stimulated directly by GHB. Most probably, GABA is released in part under the control of GHB receptors in specific pathways expressing GABAB receptors. Alternatively, GABAB receptors might be specifically stimulated by the GABA formed via the metabolism of gamma-hydroxybutyrate in brain. In animals and man, these GHBergic and GABAergic potentiations induce dopaminergic hyperactivity (which follows the first phase of dopaminergic terminal hyperpolarization), a strong sedation with anaesthesia and some EEG changes with epileptic spikes. It is presumed that, under pathological conditions (hepatic failure, alcoholic intoxication, succinic semialdehyde dehydrogenase defects), the rate of GHB synthesis or degradation in the peripheral organ is modified and induces increased GHB levels which could interfere with the normal brain mechanisms. This pathological status could benefit from treatments with gamma-hydroxybutyric and/or GABAB receptors antagonists. Nevertheless, the regulating properties of the endogenous gamma-hydroxybutyrate system on the dopaminergic pathways are a cause for the recent interest in synthetic ligands acting specifically at gamma-hydroxybutyrate receptors and devoid of any role as metabolic precursor of GABA in brain.

Purification and properties of an enzyme in human blood and rat liver microsomes catalyzing the formation and hydrolysis of gamma-lactones. II. Metal ion effects, kinetics, and equilibra.

by Fishbein WN, Bessman SP

J Biol Chem Vol 241 (21) 1966; 4842-7