PubMed · 62243
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L M Koran. 1976-11-06. gamma-Aminobutyric-acid deficiency in schizophrenia.. https://doi.org/10.1016/s0140-6736(76)90865-5
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The existence of a strionigral GABA-ergic pathway having an inhibitory effect on the nigrostriatal dopaminergic system has been proposed. The work reported in this paper was undertaken to investigate whether modification of the GABA-eric system by the GABA neuronal uptake inhibitor DL-2,4-diaminobutyric acid (DABA) would affect cholinergic (pilocarpine) and/or neuroleptic alpha-flupenthixol (alpha-FPT) induced catalepsy. DABA pretreatment was shown to enhance significantly both alpha-FPT and pilocarpine induced catalepsy. DABA alone had no cataleptic activity. The results are interpreted as supporting the existence of an inhibitory strionigral GABA-ergic pathway.
Cystathionine gamma-synthetase (EC 4.2.99.9), a key enzyme in bacterial methionoine biosynthesis, has been found to use L-vinylglycine (2-amino-3-butenoate) and L-beta-haloaminobutyrates (X = F, Cl) as substrates in addition to the physiological gamma-substituted substrate O-succinyl-L-homoserine (OSHS). Vinylglycine is a substrate both for alpha-ketobutyrate formation (the normal product from gamma elimination with OSHS) and for cystathionine formation (the normal gamma-replacement product with OSHS) in the presence of cysteine. This behavior substantiates that the stabilized vinylglycine--pyridoxal phosphate (PLP) alpha carbanion is the key partitioning species in this enzyme's catalysis. The Vmax values for ketobutyrate production and cystathonine formation from vinylglycine are equivalent at approximately 45 U/mg, whereas the corresponding Vmax values from OSHS are 20 and 200 U/mg, respectively, suggesting different rate-determining steps with these two substrates. The beta-haloaminobutyrates undergo catalyzed HX elimination to yield bound aminocrotonate--PLP directly as a an initial intermediate and as a precursor of ketobutyrate. Little or no cystathionine formation is detectable when these substrates are incubated with enzyme and the normal cosubstrate cysteine, strongly indicating that the aminocrotonate--PLP intermediate is not in rapid, reversible equilibrium with the stabilized vinylglycine--PLP carbanion; in normal catalysis, the prototropic shift from alpha carbanion to aminocrotonate appears functionally unidirectional. The HX-elimination step from beta-chloroaminobutyrate is nonconcerted as demonstrated by a 3H2O in equilibrium chloroaminobutyrate exchange reaction. Further suggestion for discrete beta-halo-alpha-carbanionic intermediates derives from the observation that the haloaminobutyrates appear to a partition between ketobutyrate formation and enzyme inactivation. Since neither vinylglycine nor OSHS causes any detectable inactivation during turnover, it is likely that the inactivation species is not a common intermediate, i.e., the electrophilic aminocrotonate--PLP species (a potential Michael acceptor), but rather a species peculiar to the beta-haloaminobutyrate pathway. The beta-halo-alpha-carbanion--PLP intermediate has beta-halo-alpha-iminodihydropyridine character in the p-quinoid resonance contributor and is a good candidate for an alkylating agent by an SN2--displacement mechanism. Spectroscopic analyses of incubations with the various amino acid substrates show a number of long-wavelength absorbing species forming during turnover, tentative assignments are suggested.
Intravenous baclofen (1 mg/kg) abolished or severely attenuated the high threshold late component (but not the low threshold early component of long duration (greater than 150 msec) discharges evoked in cat dorsal horn neurons by intense transcutaneous electrical stimulation. Baclofen similarly reduced the spontaneous activities and discharges evoked by intra-arterial bradykinin in these same cells. These powerful inhibitions of dorsal horn interneurons may be the basis of baclofen's reported analgesic actions and could contribute to depression in reflex excitability of motoneurons.