The accumulation and metabolism of amino acids by Biomphalaria glabrata, a freshwater pulmonate snail

Freshwater pulmonate snails (Biomphalaria glabrata), pre-treated under bacteriostatic conditions, were incubated in 10 ml of standard medium containing various U-¹⁴C-labelled amino acids at concentrations of 10 μM. Measurements of mass-specific accumulation rates (MSARs) based on HPLC and the accumulation of U-¹⁴C-labelled amino acids into snail tissues have shown unequivocally for the first time that freshwater snails achieved a net accumulation of all the amino acids tested, including aminoisobutyrate (AIB), aspartate, alanine and a mixture of 13 amino acids. There were no significant differences between the MSAR values determined by HPLC from those based on the use of radiolabelled amino acids, whereas MSAR values for control snails were negligible and significantly less. Incubation of snails in media containing radiolabelled aspartate and a mixture of amino acids showed that the accumulated amino acids were readily distributed through the snail’s tissues and then metabolized. The ecological and biochemical questions arising from the fact that freshwater snails are capable of net accumulation of exogenous amino acids at naturally occurring concentrations and subsequent metabolic conversion, contrary to widely held views, are addressed.     

Comparative studies of zinc metabolism in cultured chinese hamster cells with differing metallothionein-induction capacities

Previous work in our laboratory led to the isolation of a cadmium (Cd)-resistant variant (Cd^r2C10) of the line CHO Chinese Hamster cell having a 10-fold greater resistance to the cytotoxic action of Cd²⁺ compared with the CHO cell. This resistance was attributed to an increased capacity of the Cd²⁺-resistant Cd^r2C10 subline to induce synthesis of the Cd²⁺- and Zn²⁺-binding protein(s), metallothionein(s) (MT). Evidence that Cd²⁺ behaves as an analog of the essential trace metal, Zn²⁺, especially as an inducer of MT synthesis, suggested that the Cd^r and CHO cell types could be employed to investigate cellular Zn²⁺ metabolism. In the present study, measurements were made to compare CHO and Cd^r cell types for (a) growth as a function of the level of ZnCl₂ added to the culture medium, (b) uptake and subcellular distribution of Zn²⁺, and (c) capacity to induce MT synthesis. The results of these measurements indicated that (a) both CHO and Cd^r cell types grew normally (T _d≊16–18 h) during exposures to Zn²⁺ at levels up to 100 μM added to the growth medium, but displayed abrupt growth inhibition at higher Zn²⁺ levels, (b) Cd^r cells incorporate fourfold more Zn²⁺ during a 24-h exposure to the maximal subtoxic level of Zn²⁺ and (c) the CHO cell lacks the capacity to induce MT synethesis while the Cd^r cell is proficient in this response during exposure to the maximal subtoxic Zn²⁺ level. These findings suggest that (a) the CHO and Cd^r cell systems will be useful in further studies of cellular Zn²⁺ metabolism, especially in comparisons of Zn²⁺ metabolism in the presence and absence of induction of the Zn²⁺-sequestering MT and (b) a relationship exists between cellular capacity to induce MT synthesis and capacity for cellular Zn²⁺ uptake.     

“增收宝－3”中氨基酸成分

用日立８３５－５０型氨基酸分析仪对“增收宝－３”中游离的氨基酸进行了分析。结果表明其中含有１５种氨基酸,以脯氨酸含量最高。实验结果揭示,氨基酸可能是“增收宝－３”中抗逆增产的有效成分。     

“增收宝－3”中氨基酸成分

用日立８３５－５０型氨基酸分析仪对“增收宝－３”中游离的氨基酸进行了分析。结果表明其中含有１５种氨基酸,以脯氨酸含量最高。实验结果揭示,氨基酸可能是“增收宝－３”中抗逆增产的有效成分。     

氨基酸转运体在肿瘤代谢中的研究进展

代谢重编程是肿瘤的重要特征,是指肿瘤细胞为满足其快速增殖的生物合成与能量需求,对其糖代谢、脂代谢以及氨基酸代谢等代谢路径进行的重编程,以维持增长速度以及补偿能量代谢所造成的氧化还原压力。虽然不同的癌症代谢变化不同,但有些特征是所有癌症共有的,氨基酸代谢重编程是其中一个重要的特征。氨基酸进出细胞需要氨基酸转运体的协助,因而在肿瘤细胞中多种特定的氨基酸转运体均过表达。靶向氨基酸转运体通过影响肿瘤细胞的氨基酸代谢从而达到抗肿瘤的目的,是目前抗肿瘤药物的研究热点之一。主要介绍了几种在肿瘤代谢中发挥重要作用的氨基酸转运体以及靶向氨基酸转运体抗肿瘤治疗的研究进展及相关作用机制,旨在了解氨基酸转运体在抗肿瘤研究中的作用,以期促进靶向氨基酸转运体抗肿瘤药物的发展。     

谷氨酰胺对微囊化重组CHO细胞生长代谢及内皮抑素表达的影响

微囊化技术是一种有发展潜力的生物技术,在细胞移植和药物控释等方面具有广泛的应用。然而由于目前微囊化细胞规模化培养技术还不成熟,阻碍了其在临床治疗中的推广与应用。为了了解微囊化重组CHO细胞的生长代谢特性为今后规模化培养优化提供技术参考,考察了主要氮源物质谷氨酰胺对微囊化重组CHO细胞生长代谢及内皮抑素表达的影响。结果显示:当谷氨酰胺起始浓度从2.69mmolL增加到9.05mmolL时最大活细胞密度并没有增高,细胞增殖没有显著差异。当谷氨酰胺起始浓度较低(2.69mmolL)时,葡萄糖的比消耗速率较大;当谷氨酰胺起始浓度增高时(7.91mmolL～9.05mmolL)葡萄糖和谷氨酰胺的比消耗速率增大,但细胞对葡萄糖和谷氨酰胺的利用率降低。谷氨酰胺对产物表达有显著影响,起始浓度为4.97mmolL时的内皮抑素累积浓度最高,达546.36ngmL,过低和过高谷氨酰胺起始浓度下内皮抑素的累积浓度均较低。     

Growth-promoting Activity of an Aqueous Extract of Soybean Seeds for Some Microorganisms

The metabolic fates of the carbon skeletons of leucine, lysine, and threonine were studied in growing rats on the diets containing graded levels of protein calorie percentages (10, 20, 30, and 40PC%) by use of either gluten or zein at 4100 kcal of metabolizable energy per kg of diets. In growth experiment for 21 days, body weight gain, food intake, and body fat increased at higher PC% in the gluten diets, but rats given zein did not maintain their initial weight even at 40PC%. The concentration of plasma free lysine remained low with the zein diets, but plasma threonine increased at 10 and 20PC% in the gluten and zein diets, respectively. Plasma leucine increased as the protein level increased either dietary protein. More than 70% of ¹⁴C was incorporated into body protein 12 h after an intraperitoneal injection of labeled lysine in all groups, but little ¹⁴CO₂ was expired in rats on the gluten and zein diets. About 79% of ¹⁴C-threonine was incorporated into body protein in rats given the gluten and zein diets at 10PC%, but the values were gradually decreased with increasing the dietary protein levels. Some 40–50% of ¹⁴C-leucine was incorporated into the body protein in rats given the gluten diets, and the values for the zein diets were extensively decreased in the higher PC% groups where the expired ¹⁴CO₂ was inversely increased to a great extent. These results showed that, when a specific amino acid was limiting or deficient in the diet, the major portion of the labeled amino acid was utilized for body protein synthesis and little was oxidized to carbon dioxide, whereas the oxidative degradation of essential amino acid other than limiting one was increased and the efficiency of the amino acid utilization was relatively decreased.     

The effect of osmolarity on metabolism and morphology in adhesion and suspension chinese hamster ovary cells producing tissue plasminogen activator

The effects of constant osmolarity, between 300 and500 mOsm/kg, on the metabolism of Chinese HamsterOvary (CHO) cells producing tissue plasminogenactivator (tPA) were compared between adhesion andsuspension cultures. In both suspension and adhesionculture, the specific rates of glucose consumption(_G), lactate production (q_L), and tPAproduction (q_tPA) increased as osmolarityincreased, while these rates decreased when osmolaritywas higher than the respective critical levels. However, specific growth rate () decreased withincrease in osmolarity and this slope grew steeper inthe osmolarity range higher than the critical level. The decrease in in the adhesion culture was morerapid than that in the suspension culture. Thecritical osmolarity for adhesion culture (400 mOsm/kg)was lower than that for suspension culture (450 mOsm/kg). These results indicated that the adhesionculture was more sensitive to increase of osmolaritythan the suspension culture, while the specific ratesobtained from the adhesion cultures were in general1.5- to 3-fold higher than those obtained from thesuspension cultures. Cell volume increased asosmolarity increased in both the suspension andadhesion cultures, as reported previously forsuspension culture of hybridoma cells, but there wasno morphological change in the suspension culture. Incontrast, cell height decreased and cell adhesion areamarkedly increased as osmolarity increased in theadhesion culture. This morphological change inadhesion cultures may be one reason for the highersensitivity of adherent cells to the increase ofosmolarity than suspended cells.     

Ornithine transaminase from Cucurbita maxima cotyledons

During germination a marked increase in both soluble and particulate ornthine transaminase occurs in pumpkin cotyledons. Both enzymes had a pH optimum of 8.3 and a requirement for ornthine and α-ketoglutarate. Other keto acids or amino donors showed little activity. The enzymes required an active sulphydryl group for maximum activity. Exogenous pyridoxal phosphate was not required, but hydroxylamine inhibited the reaction and added pyridoxal phosphate overcame this inhibition. Proline inhibited the reaction and may play a role in the fate of ornithine in pumpkin cotyledons.     

槲皮素对甲硫氨酸负载大鼠氨基酸代谢的影响

为探讨槲皮素对甲硫氨酸(Met)负载大鼠氨基酸代谢的影响,将Wistar大鼠24只随机分为3组,即对照组、1％甲硫氨酸组以及1％甲硫氨酸和0.5％槲皮素组,喂养6周后,采用高压液相色谱法测定血清中半胱氨酸含量,全自动氨基酸分析仪测定血清中其他氨基酸含量.结果显示,1％甲硫氨酸干预后除对牛磺酸产生显著影响外,对其他氨基酸没有明显影响.0.5％槲皮素干预后,血清必需氨基酸苏氨酸、缬氨酸含量较1％ Met组显著升高(p＜0.05),牛磺酸、缬氨酸、亮氨酸和异亮氨酸较对照组亦显著升高(p＜0.05),而血清丝氨酸和脯氨酸含量较对照组显著降低(p＜0.05).结果表明,槲皮素可能加强甲硫氨酸转硫化代谢途径.     

Effect of Bcl‐xL overexpression on lactate metabolism in chinese hamster ovary cells producing antibody

Previously, overexpression of anti‐apoptotic proteins, such as E1B‐19K and Aven, was reported to alter lactate metabolism of CHO cells in culture. To investigate the effect of Bcl‐x_L, a well‐known anti‐apoptotic protein, on lactate metabolism of recombinant CHO (rCHO) cells, two antibody‐producing rCHO cell lines with regulated Bcl‐x_L overexpression (CS13*‐0.02‐off‐Bcl‐x_L and CS13*‐1.00‐off‐Bcl‐x_L) were established using the Tet‐off system. When cells were cultivated without Bcl‐x_L overexpression, the specific lactate production rate (q_Lac) of CS13*‐0.02‐off‐Bcl‐x_L and CS13*‐1.00‐off‐Bcl‐x_L were 7.32 ± 0.37 and 6.78 ± 0.56 pmol/cell/day, respectively. Bcl‐x_L overexpression, in the absence of doxycycline, did not affect the q_Lac of either cell line, though it enhanced the viability during cultures. Furthermore, activities of the enzymes related to glucose and lactate metabolism, such as hexokinase, glucose‐6‐phosphate dehydrogenase, lactate dehydrogenases, and alanine aminotransferase, were not affected by Bcl‐x_L overexpression either. Taken together, Bcl‐x_L overexpression showed no significant effect on the lactate metabolism of rCHO cells. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1594–1598, 2013     

氨基酸转运载体LAT1研究进展

哺乳动物氨基酸的跨膜运输由多种氨基酸转运载体蛋白介导,其中L型氨基酸转运载体1（LAT1）属于L系统,主要转运大分子支链氨基酸和芳香族中性氨基酸。研究表明,LAT1广泛存在于哺乳动物肝脏、骨髓、大脑、胎盘、心脏和睾丸组织中,LAT1在恶性肿瘤中大量表达,对其不断的增殖起着重要的作用。目前国内对氨基酸转运载体LAT1的研究仍是空白,鉴于LAT1的研究在医学、营养等生命科学领域的研究意义,本文就氨基酸转运载体蛋白LAT1的表达、调节及其相关研究进展作一综述。     

Evidence for a regulatory element controlling amino aced transport system L in Chinese hamster ovary cells

We have used the technique of somatic cell hybridization to study the regulation of the neutral amino acid transport system L in Chinese hamster ovary (CHO) cells. The cell line CHO–;tsO25C1 has a temperature-sinsitive mutationin leucyl-tRNA synthetase. At the nonpermissive temperature of 39^oC, CHO–tsO25C1 cells are unable to charge leucyl-tRNA and behave as though starved for leucine by increasing their system L transport activity two- to fourfold. From the temperature-sensitive cell line, we have isolated a regulatory mutant cell, CHO–C11B6, that has constitutively elevated system L transport activity. The CHO–C11B6 cell line retains the temperature-sensitive leucyl-tRNA synthetase mutation, but growth of this cell line is temperature resistant because its increased system L transport activity leads of increased intracellular leucine levels, which compensate for the defective. Hybrid cells formed by fusion of the temperature-sensitive CHO–;tsO25C1 cells the temperature-resistant CHO–C11B6 cells show temperature-sensitive growth and temperature-dependent regulation of leucine transport activity. These data suggest that the system L activity of CHO cells is regulated by a dominant-acting element that is defective or absent in the regulatory mutant CHO–C11B6 cell line.