羧酸盐对鸭肝脂肪酸合成酶的抑制作用

本文研究了一系列羧酸盐对鸭肝脂肪酸合成酶的抑制规律,抑制动力学以及对几个含羧基的巯基试剂修饰该酶的保护动力学,并计算了相应的在酶上结合的平衡常数。提出羧酸盐结合于该酶缩合中心区域一个可结合羧基负离子的部位,该部位也是丙二酰基的结合部位,它可使携带了丙二酰基的活臂向缩合中心定向运动,并为缩合活性所必需。     

THE SUBCELLULAR LOCALIZATION OF CYTIDINE 5''-MONOPHOSPHO-N-ACETYLNEURAMINIC ACID SYNTHETASE IN CALF BRAIN

Abstract— The subcellular distribution of cytidine 5'-monophospho- N -acetylneuraminic acid synthetase, which is a key enzyme involved in the biosynthesis of sialo-glycoproteins and gangliosides, was studied in the frontal grey cortex and the corpus callosum of the calf brain. It appeared that the enzyme was highly concentrated in nuclear fractions, which were shown to be relatively pure as evaluated from morphological, enzymic and chemical data. The possibility that the nuclear localization of the enzyme was due to an artifact, as the result of adsorption onto the nuclear membrane or absorption into the nucleus during the homogenization of the tissue, was ruled out completely and so it appeared that cytidine 5'-monophospho- N -acetylneuraminic acid synthetase, at least for the greater part, is a true nuclear enzyme. The subnuclear localization of the enzyme was shown to be in the nuclear sap. Both neuronal and glial cell nuclei contained the enzyme, which makes it very likely that biosynthesis of sialo-glycoproteins and/or gangliosides occurs in neurons as well as in glial cells. The significance of the nuclear localization of the enzyme for the biosynthesis of sialic acid containing macromolecules and the possible regulatory role played by the nucleus in this process are discussed.     

THE REGIONAL DISTRIBUTION OF CYTIDINE 5''-MONOPHOSPHO-N-ACETYL-NEURAMINIC ACID SYNTHETASE IN CALF BRAIN

—The enzyme cytidine 5′-monophospho-N-acetylneuraminic acid synthetase was studied in different parts of the calf brain. Characterization of partial purified enzyme preparations from cortical grey matter and corpus callosum by means of pH optima and K_m values, showed the enzyme of grey and white brain areas to be identical. Unexpectedly the regional differences of the enzyme activities per g wet tissue and per mg protein were very slight. From the presence of the enzyme in pure white brain areas, which are known to be poor in neuronal perikarya, and the fact that the enzyme is localized in the cell nucleus, we concluded that cytidine 5′-monophospho-N-acetylneuraminic acid is produced in glia cell nuclei and that it is very likely that biosynthesis of sialo-glycoproteins and/or ganglio-sides occurs within glia cells. The enzyme activity per μmol DNA-P is somewhat higher in grey than in white regions, indicating a slightly higher activity per neuronal than per glial nucleus. The regional differences of lipid and protein-bound sialic acid and RNA show a striking similarity and contrast to those of the enzyme. These differences are interpreted in terms of a differential content in neurons and glia cells.     

FATTY ACID SYNTHETASE OF BRAIN: DEVELOPMENT, INFLUENCE OF NUTRITIONAL AND HORMONAL FACTORS AND COMPARISON WITH LIVER ENZYME

Abstract— The activity of fatty acid synthetase was studied in the brain and liver of the developing rat. Synthetase activity in brain was considerably higher in foetal and suckling rats than in older animals However, except for a small transient rise in the perinatal period, activity in liver was low until weaning when a dramatic rise occurred. Activity in brain varied according to the quantity of dietary fat only in long-term experiments, whereas in liver nutritional influences clearly predominated in determining the rapid developmental changes of synthetase activity. Administration of hydrocortisone diminished hepatic activity but did not change brain synthetase. In the hypothyroid state activity in brain and liver was consistently decreased. However, in the hyperthyroid state hepatic activity increased but activity in brain did not change. The relatively high activity of fatty acid synthetase during brain development has been discussed in relation to the critical role of this enzyme system in brain metabolism. The effect of the hypothyroid state on the activity of brain synthetase suggests the possibility of hormonal control of this enzyme activity. The responses of hepatic synthetase to the hormonal influences delineate a specific step by which these compounds may exert their effect on fatty acid biosynthesis.     

谷氨酰胺合成酶活性与水稻杂种优势预测

从杂种优势预测生理指标需具备的３个基本条件入手,对杂交水稻及其亲本生长发育过程中的谷氨酰胺合成酶活性进行研究,结果表明：水稻ＧＳ活性在整个生育期中的变化呈现一定的规律性,并且杂种酶活性是由其双亲遗传性所决定的;同时,ＧＳ活性与多个生理性状及产量性状具有一定的相关性;在孕穗期和抽穗期与产量性状的关系尤为密切,因此,在生死生长期ＧＳ活性在一定程度上可以反映产量性状的优势水平,可望作为水稻杂种优势预测的     

谷氨酰胺合成酶活性与水稻杂种优势预测

从杂种优势预测生理指标需具备的３个基本条件入手,对杂交水稻及其亲本生长发育过程中的谷氨酰胺合成酶（ＧＳ,ＥＣ６、３、１、２）活性进行研究,结果表明：水稻ＧＳ活性在整个生育期中的变化呈现一定的规律性,并且杂种酶活性是由其双亲遗传性所决定的;同时,ＧＳ活性与多个生理性状及产量性状具有一定的相关性;在孕穗期和抽穗期与产量性状的关系尤为密切,因此,在生殖生长期ＧＳ活性在一定程度上可以反映产量性状的优势水平,可望作为水稻杂种优势预测的一个辅助指标。     

FLUCTUATIONS IN FREE AMINO ACID POOLS OF GYMNODINIUM SIMPLEX (DINOPHYCEAE) IN RESPONSE TO AMMONIA PERTURBATION: EVIDENCE FOR GLUTAMINE SYNTHETASE PATHWAY1,2

An ammonia limited chemostat culture of Gymnodinium simplex (Lohm.) Kofoid & Swezy was perturbed with ammonia and fluctuations in the free intracellular amino acid pools were followed 80 min. The steady-state value of glutamate was 2.07 ± 10^-15 mol cell^-1 and of glutamine was 0.31 ± 10^-15 mol cell^-1. Five minutes after the perturbation, a substantial rise in glutamine was observed with a corresponding decrease in glutamate. This is considered a result of glutamine synthetase acting as the primary ammonia assimilating enzyme. The level of ammonia and the major free amino acids reached a maximum 10 min after the perturbation and then slowly decreased.     

CTP SYNTHETASE ACTIVITY IN NEONATAL AND ADULT RAT BRAIN

—The activity of CTP synthetase (UTP:ammonia ligase (ADP-forming), EC 6.3.4.2) in adult and new-born rat brain was determined by an enzyme assay using [¹⁴C]UTP as a substrate. The activity was age-dependent and showed a distinctive distribution pattern between the cerebral hemispheres and cerebellum. The possible correlations between the activity of CTP synthetase and the rate of RNA or lipid biosynthesis, as well as the regulatory importance of the enzyme in the formation of cytidine nucleotides are discussed.     

林肯链霉菌谷氨酰胺合成酶的酶学性质

在分离纯化的基础上,报道了pH、温度和金属离子对林肯链霉菌(Streptomyceslincolnensis)Z-512谷氨酸胺合成酶(GS)活力的影响及GS底物专一性的研究结果.在动力学性质的研究中,发现林肯链霉菌GS在生物合成反应系统中,对底物NH_4CI的饱和曲线不遵守米氏方程.Hill作图呈两相曲线.在NH_4CI浓度低的情况下,Hill系数大于1,具有正协同效应;当NH_4CI浓度增加到一定程度时,Hill系数小于1,具有负协同效应.这说明NH_4CI不仅作为林肯链霉菌GS的底物,而且作为一种效应物调节GS的活性.林肯链霉菌GS对底物Glu及ATP的饱和曲线遵守米氏方程.在不同的激活离子存在下,GS对Glu、ATP的Km值也不同.     

不同氮源对小麦幼苗谷氨酰胺合成酶的影响

利用ＤＥＡＥ－纤维素柱层析、酶活性测定、Ｎｏｒｔｈｅｒｎ 分子杂交等技术,研究了小麦（Ｔｒｉｔｉｃｕｍ ａｅｓｔｉｖｕｍ Ｌ．）幼苗的根、叶和离体叶在不同氮源培养条件下谷氨酰胺合成酶（ＧＳ）活性和同工酶变化, 以及不同氮源对ＧＳ基因转录－ＧＳ－ｍ ＲＮＡ 的影响． 同时与硝酸还原酶（ＮＲ）活性进行比较, 结果表明∶当以ＮＨ＋４ 作唯一氮源时,小麦幼苗根谷氨酰胺合成酶（ＧＳｒ）和叶细胞质谷氨酰胺合成酶（ＧＳ１）活性要比以ＮＯ－３ 作唯一氮源的高．当以ＮＯ－３ 为唯一氮源时, ＮＯ－３ 则促进完整叶片和离体叶片叶绿体谷氨酰胺合成酶（ＧＳ２）活性． 从转录水平上看,ＮＨ＋４ 促进根ＧＳ－ｍ ＲＮＡ 的合成,而ＮＯ－３ 促进叶ＧＳ－ｍ ＲＮＡ 的合成     

PURIFICATION AND CHARACTERIZATION OF CARNOSINE SYNTHETASE FROM MOUSE OLFACTORY BULBS

Carnosine synthetase was purified about 500-fold from mouse olfactory bulb to a specific activity of approx 25 nmol/min/mg. This is an increase of 800-fold over that previously reported for this enzyme from rat brain and 11 times higher than the most highly purified enzyme from chicken pectoral muscle. ATP was essential for activity and could not be replaced by ADP. NAD had no effect on the synthesis of carnosine. Of the β-alanine analogues tested, the purified mouse enzyme incorporated only γ-aminobutyric acid and β-amino-n-butyric acid into peptide linkage with histidine. Synthesis of carnosine by the mouse olfactory bulb enzyme was competitively inhibited by the histidine analogues, 1-methyl histidine and 3-methyl histidine, with K_i values which were at least 40 times the K_m value for histidine (16 μM). Ornithine and lysine were more efficient β-alanine acceptors than 1-methyl histidine for the mouse enzyme. Enzyme from olfactory epithelium and leg skeletal muscle of mice also showed higher K_i values for 1–methyl histidine than the K_m value for histidine. In contrast, carnosine-anserine synthetase from chicken pectoral muscle gave K_m values for histidine, 1-methyl histidine and 3-methyl histidine, which were all in the range of 4–12 μM. The differences in substrate specificity between the enzyme from mouse and chicken implies alternate routes of anserine synthesis in these species and predicts the occurrence of certain novel peptides in mouse brain.     

林肯链霉菌谷氨酰胺合成酶活力调节的研究

对不同氮源生长条件下林肯链霉菌无细胞粗提液中谷氨酰胺合成酶 (GS)的研究结果表明 ,高浓度NH+4阻遏了GS的生物合成。从不同氮源生长条件下林肯链霉菌中分离纯化了GS ,其性质没有差别。以受腺苷化调节的产气克雷伯氏菌GS作对照 ,林肯链霉菌GS没有明显的氨休克作用 ,经蛇毒磷酸二酯酶处理后 ,其活力没有变化。这些结果都说明林肯链霉菌GS不存在腺苷化共价修饰这一调节方式。反馈抑制作用是林肯链霉菌GS的一种重要的调节方式 ,这种抑制作用是以累积的方式进行的 ,这表明各种抑制剂对GS作用位点不同 ,各种抑制剂对GS的抑制作用是相互独立的。由此推测 ,林肯链霉菌GS是一种变构酶。