INHIBITION OF THE UPTAKE OF GABA AND RELATED AMINO ACIDS IN RAT BRAIN SLICES BY THE OPTICAL ISOMERS OF NIPECOTIC ACID

R(-)-Nipecotic acid was a more potent inhibitor than the S(+)-isomer of the uptake of GABA, (+)-nipecotic acid, and β-alanine in rat brain slices. (-)-Nipecotic acid was an order of magnitude more potent as an inhibitor of GABA uptake than as an inhibitor of β-alanine uptake, whereas the (+)-isomer was less selective. (–)-Nipecotic acid was a weak inhibitor of L-proline uptake and of rat brain acetylcholinesterase activity. Kinetic studies showed that both isomers of nipecotic acid were competitive inhibitors of GABA uptake when added at the same time as GABA, but non-competitive inhibitors when preincubated with the tissue for 15 min before addition of GABA. The apparent slope inhibition constants, which were not influenced by preincubation, indicated that (–)-nipecotic acid has an affinity for the carrier some 5 times higher than that for (+)-nipecotic acid. (–)-Nipecotic acid stimulated the release of preloaded radioactive GABA from rat brain slices. These observations indicate that (–)-nipecotic acid is a substrate-competitive inhibitor of GABA which combines with the GABA carrier and is taken up. (?)-Nipecotic acid and (+)-2,4-diaminobutyric acid, on the basis of their absolute structures and inhibition kinetics, are proposed to interact in a similar way with the GABA transport system.     

AROMATIC AMINOTRANSFERASE ACTIVITY OF RAT BRAIN CYTOPLASMIC AND MITOCHONDRIAL ASPARTATE AMINOTRANSFERASES

Abstract— Mitochondrial and cytoplasmic forms of aspartate aminotransferase were purified from rat brain homogenates and tested for their ability to catalyze transamination of various aromatic amino acids. The mitochondrial enzyme exhibited activity toward tyrosine and phenylalanine with 2-oxoglutar-ate as acceptor, although the specific activities were less than 1% of the corresponding aspartate activity when all substrates were 10 mM. Even less activity was seen with DOPA, 5-hydroxytryptophan and tryptophan. The cytoplasmic aspartate aminotransferase was active toward tryptophan, 5-hydroxytryptophan and DOPA, but these transaminations were favored by pyruvate or oxaloacetate rather than 2-oxoglutarate as keto acid. Based on co-migration of aromatic activities with the respective aspartate aminotransferases during isoelectric focusing and based on equal sensitivities of aromatic transamination and aspartate transamination to inhibition by vinylglycine, it was concluded that all activities resided in the aspartate aminotransferase enzymes. Some doubt exists, however, as to the physiological significance of these alternate activities in view of the requirement that aromatic amino acids must compete with aspartate for transamination by these enzymes.     

蚕氨基酸代谢的研究——家蚕与蓖麻蚕的氨基酸和形成甘氨酸、丙氨酸的酶系比较及酮丙二酸的脱羧作用

家蚕(Bombyx mori L.)与蓖麻蚕(Samia,ricini B)的丝蛋白氨基酸含量差异甚为显著;家蚕丝含量最多的为甘氨酸(42.8％),其次为丙氨酸(32.4％);而蓖麻蚕丝则以两氨酸含量为最高(50.5％),其次为甘氨酸(27.8％)(Kirimuru等,1962)。为了阐明丝蛋白主要氨基酸的形成机制,我们曾报道了这两种蚕丝腺中,自L-天门冬氨酸与α-酮戊二酸形成丙氨酸的机制(许延森等,1964a);体液乙醛酸及丙酮酸与丝蛋白相应氨基酸的含量之     

ANALYSIS OF THE MAJOR AMINO ACIDS OF RAT BRAIN AFTER IN VIVO INHIBITION OF GABA TRANSAMINASE BY ETHANOLAMINE O-SULPHATE

The effect of in vivo inhibition of GABA transaminase by ethanolamine O-sulphate on the content of the free amino acids in rat brain has been studied. Intracisternal injection of 2.0 mg/kg resulted in a progressive increase in GABA levels with time, to reach after 8 h a 100 per cent increase over saline-injected control animals. The effect of injection of 0.5, 1.0 and 2.0 mg/kg was studied 24 h after injection and the results showed that the increased GABA levels were dependent on the dose of inhibitor employed. Apart from the substantial increase in the GABA concentration of the brain there were no significant changes in the content of the other amino acids except for a small but significant decrease in aspartic acid in one experiment. When the extent of inhibition of the transaminase was correlated with the rise in GABA concentration it was shown that no elevation occurred until more than half of the enzymic activity had been inhibited.     

SECRETION OF VITAMINS AND AMINO ACIDS INTO THE ENVIRONMENT BY OCHROMONAS DANICA1,2

Ochromonas danica grown on a chemically defined medium under controlled conditions in the light synthesized the following vitamins: ascorbate, B₆, N⁵-methyltetrahydrofolate, tetrahydrofolate polyglutamates, oxidized folate monoglutamates, nicotinate, pantothenate, riboflavin, vitamin A, β-carotene, and vitamin E but no vitamin. B₁₂. The cells also secreted molecules into their growth medium including the vitamins ascorbate, B₆, the above folates, nicotinate, pantothenate, riboflavin, vitamin E, and the amino acids alanine, aspartic acid, leucine, and valine. The role of such secretions in nature is discussed.     

REVERSAL OF d-CYCLOSERINE INHIBITION OF BACTERIAL GROWTH BY ALANINE.

Zygmunt, Walter A. (Mead Johnson & Co., Evansville, Ind.). Reversal of d-cycloserine inhibition of bacterial growth by alanine. J. Bacteriol. 84:154-156. 1962.-Reversal of the antibacterial activity of d-4-amino-3-isoxazolidone by alanine in bacterial cultures actively growing on chemically defined media was compared in cultures requiring exogenous alanine and those capable of its synthesis. dl-Alanine was the most effective reversal agent in Pediococcus cerevisiae, an alanine-requiring organism, and d-alanine was effective in Escherichia coli and Staphylococcus aureus, organisms synthesizing alanine. With all three cultures, l-alanine was the least effective reversal agent.     

INHIBITION PATTERN BY ANALOGS INDICATES THE PRESENCE OF TEN OR MORE TRANSPORT SYSTEMS FOR AMINO ACIDS IN BRAIN CELLS

Abstract— We surveyed the transport systems present in the brain for amino acids. Cellular transport was measured in brain slices, and capillary transport was estimated by measuring in vivo the short-term (15 s) extraction by brain from the blood. Specific analog inhibition of uptake was used to distinguish the classes. Amino acid levels (close to physiological) were such that primarily the 'low-affinity' transport was measured.
In brain tissue we could distinguish 10 overlapping amino acid transport classes. Five of these, described in a number of tissues, were characterized by their substrates: alanine (A system), leucine (L system), alanine-serine-cysteine (ASC system), glutamic acid (Glu system), and arginine (Ly⁺ system), respectively. The others distinguished were each fairly specific for one of the following five amino acids: glycine, proline, γ-aminobutyric acid (GABA), taurine, and lysine. Of these 10 systems only 4 could be clearly found in capillary transport: L, ASC, Ly ⁺, and Glu.
The properties and the distribution of the transport systems are different. Examples are that at least one of the systems is present primarily only in neurons (GABA), and one primarily in glia (taurine). The specificity of some of the systems, e.g. A, is altered during development. In contrast to the properties of most other systems, there is little Na⁺, energy, or temperature dependence of the L system. This is reflected in the properties of capillary neutral amino acid transport when the L system is the predominant one.     

THE AMINO ACIDS OF SOME MISTLETOES AND THEIR HOSTS

The following mistletoes and their hosts were studied: Phoradendron serotinum (Raf.) M. C. Johnst. (P. flavescens [Pursh] Nutt. var. macrophyllum Engelm.) on Juglans hindsii Jeps. (California black walnut), Arceuthobium campylopodum Engelmn. f. abietinum (Engelm.) Gill on Abies concolor (Gord. and Glend.) Lindl. (white fir) and A. magnifica A. Murr (red fir), Arceuthobium campylopodum Engelm. f. campylopodum (Engelm.) Gill on Pinus sabiniana Dougl. (Digger pine), and Amyema pendula (Spleng) Tiegh. on Eucalyptus macrorhyncha F. Muell. ex Benth. (stringybark). With the exception of the Amyema leaves, the mistletoes are richer in free and bound amino acids than their hosts; moreover, their amino acid composition closely resembles that of their hosts. Nevertheless, there is no satisfactory evidence that mistletoe specificity depends on the amino acid composition of the hosts. Some mistletoes contain γ-aminobutyric acid and asparagine, not found in all hosts. All the above mistletoes but no hosts contain free hydroxyproline. These results are discussed in relation to (1) the region in the mistletoes where hydroxyproline is formed and (2) the possibility of using certain amino acid analogs as selective poisons for mistletoes.     

TRANSPORT OF AMINO ACIDS BY THE SOIL ALGA STICHOCOCCUS BACILLARIS1

The green alga Stichococcus bacillaris Naeg. is able to take up at least eleven amino acids. All of these except glutamic and aspartic acids are transported by carrier systems that obey saturation kinetics. The acidic amino acids enter the cell by passive diffusion. Michaelis-Menten parameters (K_s and V_max) were calculated for several amino acids. All obey simple Michaelis-Menten behavior except for 2-methylalanine and leucine which may have double carrier systems of different affinities. Interactions between pairs of amino acids suggest that there is at least one carrier system specific for basic amino acids and probably several systems specific for neutral amino acids. Further analysis of neutral amino acid interactions reveal that the uptake of several amino acids is incompletely inhibited by competitor uptake at infinite concentration. The simplest interpretation of the data is the operation of three carrier systems for neutral amino acids, one of which has higher affinity and broader specificity than the other two. The amino acid carrier systems appear to operate by an active mechanism. The metabolic poison DCCD inhibits uptake up to 99%. The capacities of the neutral amino acid carrier systems are increased when cells are grown in medium containing suboptimal concentrations of nitrogen.     

STUDIES ON THE INHIBITION OF BRAIN PHOSPHO-FRUCTOKINASE BY OLEATE AND THE DETERMINATION OF FATTY ACIDS IN NORMAL AND HYPOXIC BRAIN

Abstract— Oleate inhibited phosphofructokinase activity in the brain in a way which was similar to known surface-active protein denaturants. Experimental hypoxia produced an increase in the level of fatty acids in the microsomal, but not in the cytosol fraction of the brain. It is suggested that under hypoxic conditions the influence of fatty acids on the activity of phosphofructokinase (if any) is of non-specific character.     

INHIBITION OF THE BIOSYNTHESIS OF ISOPRENOID COMPOUNDS BY PHENOLIC ACIDS IN THE RAT BRAIN

—The incorporation of [2-¹⁴C]mevalonate into nonsaponifiable lipids by rat brain homogenates is inhibited by phenolic acids derived from tyrosine. The phenyl acids derived from phenylalanine are inhibitory only at very high concentrations compared with phenolic acids. The brain is more sensitive to inhibition by the phenolic acids than the liver. These studies indicate a possible role for phenolic acids in the impairment of cerebral sterol metabolism in phenylketonuria.     

灵芝孢子粉氨基酸、脂肪酸及元素组成的研究

从灵芝Ganoderma lucidum 孢子粉中检出18种常见氨基酸,总量为7．29～7．71mg／100mg 其中甲硫氨酸含量高达3.30～3.48mg／100mg,人体必需氨基酸含量占总量的694～70.4％。灵芝孢子粉含有棕榈酸(19.8％)、油酸(55.2％)、亚油酸(16.5％)以及少量的肉豆蔻酸、硬脂酸、廿碳烯酸及廿二碳四烯酸等。对56种元素进行定量或半定量分析,结果表明灵芝孢子粉碳氮比C/N=17.57：1,含有磷1.28％、硫0.87％、硅0.92％、钾1.64mg／g钠28μg／g、钙0.713mg/g、镁0.346mg／g、铁0.64mg／g、锌420μg／g、 铜127μg／g、锰11μg/g锶609μg／g等二十多种人体必需或有益的常量元素及微量元素。