谷氨酰胺、精氨酸和亮氨酸在肠道中的信号传导(一)

动植物蛋白中谷氨酰胺和亮氨酸含量丰富且较稳定,而食物和动物体液中精氨酸含量差异较大。除在蛋白质合成中起作用外,这三种氨基酸可独自激活信号传导通路以促进蛋白质的合成,并可能抑制肠上皮细胞自噬介导的蛋白质降解。此外,谷氨酰胺和精氨酸可分别激活有丝分裂原活化蛋白激酶通路和哺乳动物雷帕霉素靶蛋白(mTOR)/p70(s6)激酶通路,从而加强粘膜细胞的迁移和修复。利用一氧化氮依赖型cGMP的信号级联,精氨酸可调节肠道多种生理活动,这有利于细胞的生存和维持动态平衡。动物体内外试验显示,谷氨酰胺和精氨酸可促进细胞增殖,并可针对养分损失、氧化损伤、应激和免疫应激来发挥不同的细胞保护作用。此外,一氧化氮存在时亮氨酸可加强肠道细胞的迁移。因此,通过细胞信号传导机制,精氨酸、谷氨酰胺和亮氨酸在肠道的生长发育和功能完善过程中发挥了关键作用。     

小肠氨基酸的代谢:动物营养的新视角

营养学的传统观点认为,小肠仅仅是消化和吸收日粮中营养物质的部位。然而,新的试验证据表明,消化道在合成和降解氨基酸的过程中起着关键的作用。日粮中几乎所有的谷氨酸和天冬氨酸在第一次通过小肠时被降解。小肠还降解肠腔内的谷氨酰胺、精氨酸、甘氨酸、鸟氨酸、脯氨酸、丝氨酸、酪氨酸以及支链氨基酸(BCAA)、组氨酸、赖氨酸、蛋氨酸、苯丙氨酸、苏氨酸、色氨酸;因此,日粮中有30%~50%的这些氨基酸不能进入门静脉循环。肠上皮细胞、上皮淋巴细胞、内腔细菌分解非必需氨基酸和支链氨基酸,而小肠内腔微生物降解所有的必需氨基酸。在营养吸收后的状态下,小肠吸收动脉中的谷氨酰胺,释放氨、丙氨酸、瓜氨酸和脯氨酸等主要含氮产物。因为日粮氨基酸是小肠黏膜细胞的主要代谢燃料,以及是小肠合成蛋白质、谷胱甘肽、多胺、NO、嘌呤和嘧啶核苷的必需前体,小肠氨基酸代谢对于维持肠黏膜细胞数量、吸收能力以及防御功能、细菌屏障和免疫反应是必需的。然而,小肠内大量的氨基酸的分解代谢减少了肠外组织对日粮中氨基酸的利用,并且改变了进入体循环的氨基酸的模型。因此,根据最新的蛋白质营养研究,过去人们一直使用的基于体组织中必需氨基酸组成的"理想蛋白质"概念必须加入所有的非必需氨基酸进行修正。这对于提高动物对日粮蛋白质的利用效率和推荐适宜的蛋白质需要量具有重要的实践意义。     

氯化锌或硫酸锌处理蛋白质补充饲料对奶牛生产的影响

高产奶牛的蛋白质需要量往往超过细菌提供的可消化蛋白质量。如果细菌降解释放出来的蛋白质在下消化道吸收,这些母牛会对之做出反应。同样,如果细菌降解能释放更多的蛋白质,并且为下段肠道消化,那么     

谷氨酰胺及其对仔猪免疫功能影响研究进展

<正>1 谷氨酰胺在体组织中的含量及变化1.1谷氨酰胺在体组织中的含量谷氨酰胺(Glutamine Gln)是哺乳类动物血液和体组织中最丰富的一种游离氨基酸,分子量为146, 含2个氨基和5个碳原子,其结构决定了它既能为其他氨基酸、蛋白质和核酸的合成提供氮源,也可以像葡萄糖一样提供碳链氧化后释放能量。Gln的正常人     

瘤胃保护性氨基酸在奶牛日粮中的应用

日粮中大部分蛋白质在瘤胃中被降解,而增加日粮蛋白质的饲喂量,随之会增加瘤胃内蛋白质的降解量。为了减少瘤胃内蛋白质的降解损失,曾采用各种措施提高日粮中瘤胃非降解蛋白质(UDP)的量,但过多的UDP又会影响微生物蛋白质的合成,导致进入小肠的微生物蛋白质的数量减少。蛋氨酸和赖氨酸被认为是合成乳和乳蛋白的主要限制性氨基酸,而添加游离的氨基酸在瘤胃中很快被降解,必需以某种形式加以保护,使其在瘤胃内稳定,在真胃释放,在小肠吸收。本文综述了瘤胃保护性氨基酸(RPAA)的保护形式、包被物、RPAA的作用以及影响RPAA利用效果的因素。     

脲酶抑制剂对肉牛消化代谢和育肥效果试验

反刍动物对蛋白质饲料的利用效率较低,主要因为蛋白质(或尿素)在瘤胃内的降解率很高,使瘤胃内氨的浓度超出微生物的利用能力,造成浪费。脲酶抑制剂具有抑制瘤胃微生物脲酶活性的特异性能,不但能降低瘤胃内氨的浓度,而且可使氨的释放速度保持平稳,有利于微生物利用氨合成蛋白质,从而提高反刍动物对蛋白质或尿素的利用效率。本试验的目的是研究不同浓度脲酶抑制剂对肉牛饲料消化率和育肥效果的影响。     

牧草青贮中蛋白质降解的抑制

本文阐述了牧草青贮过程中有关蛋白质的降解以及现阶段抑制蛋白降解的各种技术和方法.     

谷氨酰胺对草鱼肠道L-亮氨酸、L-脯氨酸吸收及肠道蛋白质合成的影响

利用肠道离体灌注模型和同位素示踪技术,研究谷氨酰胺对草鱼肠道L-亮氨酸和L-脯氨酸吸收量、肠道组织游离亮氨酸和脯氨酸量、以及对肠道蛋白质合成量的影响。结果表明:谷氨酰胺能够显著增加草鱼肠道对两种氨基酸的吸收量,显著增加肠道组织游离亮氨酸和脯氨酸量,并显著增加肠道蛋白质的合成量;将1.0mmol/L组与5.0mmol/L组谷氨酰胺的试验结果相互比较,无论是肠道吸收总量还是肠道组织游离氨基酸、新蛋白质合成量均没有显著差异;草鱼肠道在吸收亮氨酸和脯氨酸的同时,能够利用吸收的亮氨酸和脯氨酸和肠道蛋白质周转的氨基酸合成新的蛋白质,蛋白质合成量随着亮氨酸和脯氨酸浓度增加呈线性增加关系。本文结果表明,谷氨酰胺能够显著增加草鱼肠道对亮氨酸和脯氨酸的吸收量、能够显著增加肠道蛋白质的合成代谢。     

谷氨酰胺转氨酶影响牛乳凝乳特性有利于干酪生产

近日,德国学者研究了谷氨酰胺转氨酶的交联作用对牛乳凝乳的影响。结果显示,酶的交联作用对凝乳的2个阶段都有影响。在凝乳第一阶段,糖巨肽的释放受到抑制,导致凝乳时间延长。第二阶段中,     

不同降解度蛋白质的配合饲料在牛瘤胃中的效果

评定反刍家畜的饲料蛋白质时,蛋白质在瘤胃中的降解度,具有重要的意义。蛋白质降解不足,能抑制瘤胃发酵,导致饲料的消耗量降低,而蛋白质降解过多,则造成氮的不必要损失。我们的研究课题是,用不同降解度蛋白     

Growth hormone stimulates protein synthesis in bovine skeletal muscle cells without altering insulin-like growth factor-I mRNA expression

Growth hormone is a major stimulator of skeletal muscle growth in animals, including cattle. In this study, we determined whether GH stimulates skeletal muscle growth in cattle by direct stimulation of proliferation or fusion of myoblasts, by direct stimulation of protein synthesis, or by direct inhibition of protein degradation in myotubes. We also determined whether these direct effects of GH are mediated by IGF-I produced by myoblasts or myotubes. Satellite cells were isolated from cattle skeletal muscle and were allowed to proliferate as myoblasts or induced to fuse into myotubes in culture. Growth hormone at 10 and 100 ng/mL increased protein synthesis in myotubes (P < 0.05), but had no effect on protein degradation in myotubes or proliferation of myoblasts (P > 0.05). Insulin-like growth factor-I at 50 and 500 ng/mL stimulated protein synthesis (P < 0.01), and this effect of IGF-I was much greater than that of GH (P < 0.05). Besides stimulating protein synthesis, IGF-I at 50 and 500 ng/mL also inhibited protein degradation in myotubes (P < 0.01), and IGF-I at 500 ng/mL stimulated proliferation of myoblasts (P < 0.05). Neither GH nor IGF-I had effects on fusion of myoblasts into myotubes (P > 0.1). These data indicate that GH and IGF-I have largely different direct effects on bovine muscle cells. Growth hormone at 10 and 100 ng/mL had no effect on IGF-I mRNA expression in either myoblasts or myotubes (P > 0.1). This lack of effect was not because the cultured myoblasts or myotubes were not responsive to GH; GH receptor mRNA was detectable in them and the expression of the cytokine-inducible SH2-containing protein (CISH) gene, a well-established GH target gene, was increased by GH in bovine myoblasts (P < 0.05). Overall, the data suggest that GH stimulates skeletal muscle growth in cattle in part through stimulation of protein synthesis in the muscle and that this stimulation is not mediated through increased IGF-I mRNA expression in the muscle.     

Effect of the beta-adrenergic agonist L644,969 on muscle growth, endogenous proteinase activities, and postmortem proteolysis in wether lambs.

To examine the effect of a beta-adrenergic agonist (BAA) on muscle growth, proteinase activities, and postmortem proteolysis, 16 wether lambs were randomly assigned to receive 0 or 4 ppm of L644,969 in a completely mixed high-concentrate diet for 6 wk. Weight of the biceps femoris was 18.6% heavier in treated lambs. At 0 h after slaughter, treated lambs had higher cathepsin B (35.6%), cathepsins B + L (19.1%), calpastatin (62.8%), and m-calpain (24.6%) than control lambs, but both groups had similar mu-calpain activities. In both longissimus and biceps femoris muscles, treated lambs had higher protein and RNA and lower DNA concentrations. However, total DNA was not affected, indicating that the increase in muscle mass was probably due to muscle hypertrophy rather than to hyperplasia. The pattern of postmortem proteolysis was significantly altered by BAA feeding. In treated lambs, postmortem storage had no effect on the myofibril fragmentation index and degradation of desmin and troponin-T. These results indicate that the ability of the muscle to undergo postmortem proteolysis has been dramatically reduced with BAA feeding. Similar proteolytic systems are thought to be involved in antemortem and postmortem degradation of myofibrillar proteins, so BAA-mediated protein accretion is probably due, at least in part, to reduced protein degradation. To examine whether protein synthesis was altered with BAA feeding, the level of skeletal muscle alpha-actin mRNA was quantified. Longissimus muscle alpha-actin mRNA abundance was 30% greater in BAA-fed lambs. Collectively, these results indicate that dietary administration of BAA increases muscle mass through hypertrophy and that the increase in muscle protein accretion is due to reduced degradation and possibly to increased synthesis of muscle proteins.     

Protein kinetics in callipyge lambs

The objectives for this experiment were to determine the effect of the callipyge phenotype on protein kinetics. We studied callipyge and normal lambs (n = 37) at 5, 8, and 11 wk of age (n = 4 to 7/ group) to determine how protein kinetics are altered by this trait. Total protein, DNA, and RNA and calpastatin activity were measured in five skeletal muscles and in the heart, kidneys, and liver, and protein accretion rates were calculated. At 8 wk, the fractional synthesis rates of proteins in these tissues were measured in vivo using a primed, continuous 8-h infusion of [2H5]phenylalanine. Fractional rates of protein degradation were estimated by differences. At 5 wk of age, muscle weights, protein mass, protein:DNA, RNA:DNA, and calpastatin activity were higher (P < .05) for callipyge, and protein mass differences continued to increase through 11 wk. At 8 wk, fractional rates of protein synthesis and degradation were lower (P < .05) in callipyge than in normal lambs. The organs of callipyge lambs exhibited reduced growth at 11 wk. Thus, enhanced muscle growth seems to be maintained in callipyge lambs by reduced protein degradation rather than increased protein synthesis. However, we cannot exclude the possibility that the initial onset of the callipyge condition may be caused by an increase in the fractional rate of protein synthesis.     

Role of Ca2+ in corticosterone-induced muscle growth retardation

The increased plasma glucocorticoid concentration in stressful conditions stimulates muscle protein degradation, and results in growth retardation in animals. However, the mechanism is still to be clarified. The present study was undertaken to examine the participation of Ca²⁺ in the glucocorticoid action, using nifedipine (NIF), a Ca²⁺ channel antagonist. The effects of NIF on growth, differentiation, and protein degradation were examined in glucocorticoid-treated primary cultured chick muscle cells. Muscle cell growth and cell differentiation were assessed by protein content and creatine kinase (CK) activity, respectively, and the rate of myofiblillar protein degradation was estimated by the release of N ^τ-methylhistidine (MeHis). Creatine kinase activity was increased by corticosterone (CTC) and this effect was minimized by NIF. Protein content was decreased by CTC and normalized by NIF. N ^τ-methylhistidine release was significantly increased by CTC and tended to be minimized by NIF. The present results indicate that CTC increases skeletal muscle proteolysis followed by muscle growth retardation partially because of enhanced Ca²⁺ influx through the NIF-sensitive Ca²⁺ channel. Enhanced muscle differentiation by CTC is mediated also by the NIF-sensitive Ca²⁺ channel.     

白介素15对骨骼肌和脂肪组织的调节作用

白介素15(IL-15)是近年发现的一种细胞因子,存在于多种细胞和组织中,具有促进淋巴细胞和NK细胞增殖和增强它们生物活性的功能.近年的研究发现,IL-15还可阻碍骨骼肌蛋白的降解,另外可通过直接作用于脂肪细胞来降低动物体内脂肪沉积.本文从IL-15的结构、受体及对骨骼肌和脂肪组织的调节作用作一综述.     

Influence of dietary protein intake on whole-body protein turnover in chicks

1. Experiments were conducted to investigate whether or not varying dietary protein intake affects whole-body protein turnover rates in young chicks. 2. Seven-d-old single comb White Leghorn male chicks were fed on diets with protein concentrations of 0, 100, 200 or 400 g/kg diet under conditions of ad libitum or equalised feeding. At the end of the experiments, the rate of protein synthesis and protein degradation in the whole body were measured in vivo. 3. The results showed that both fractional and absolute rates of protein synthesis increased with increasing dietary protein up to 200 g/kg; above this concentration they remained almost constant when feeding was ad libitum. 4. Similar responses were found with equalized feeding except that a significant reduction in protein synthesis was found when dietary protein was increased from 200 to 400 g/kg diet. 5. Less sensitive and almost parallel changes in protein degradation rates were found. 6. It was concluded that adaptation to varied dietary protein intake occurred primarily through changes in protein synthesis, accompanied by parallel alterations in protein degradation in the whole body.     

反刍动物过瘤胃蛋白的保护措施

过瘤胃蛋白就是将一些蛋白质经过处理，避免在瘤胃内被发酵、降解，而直接进入小肠后再被消化吸收，从而达到提高饲料蛋白质利用率的目的。保护饲料蛋白免遭微生物过量降解，提高蛋白质的总体利用率的方法有许多，主要有物理方法、化学方法、生物学调控、瘤胃外流速度的调控、利用食管沟反射提高过瘤胃蛋白等。本文就目前蛋白质的各种过瘤胃保护途径和效果进行了综述。     

瘤胃微生态种群对宿主动物氮源物质的调节作用研究

瘤胃微生物如细菌、原虫以及纤毛虫等的研究一直是反刍动物研究的重要方面。它们不仅可以对饲料纤维、淀粉进行降解,日粮蛋白质也是它们的发酵底物之一,此外,内源性的含氮物质和日粮中添加的氮源物质都可被它们代谢利用。在瘤胃微生物产生的各种降解酶的作用下,饲料养分被逐级降解进行转化,但它们的作用机理及相互作用尚不完全清楚,一直是反刍动物营养研究的重点。为此,文章对瘤胃微生物对宿主动物氮源物质的作用及其需求作一介绍,以便为深入研究作一参考。     

钙蛋白酶系统在肌肉生长和肉品嫩化方面的研究

钙蛋白酶系统主要由钙蛋白酶(calpain)及钙蛋白酶抑制蛋白(calpastatin)组成,calpain是存在于细胞质中的依赖于Ca2+的中性蛋白酶,calpastatin是钙蛋白酶的内源抑制蛋白。近年的研究表明,calpain是细胞质中主要的蛋白水解酶,在肌原纤维蛋白降解中起着重要的作用。肌肉增长和宰后嫩度的变化与蛋白质水解程度密切相关。因此,钙蛋白酶系统的活性会影响畜禽肌肉增长和肉的嫩度。文中综述了钙蛋白酶系统各种酶的结构及其如何在肌肉生长和肉的嫩化中起作用。     

Protein turnover and sensory traits of longissimus muscle from implanted and nonimplanted heifers

Primary bovine muscle cell culture studies were conducted to determine whether implanting heifers had a direct effect on in vitro protein synthesis and degradation and to determine the effect of implanting heifers on longissimus muscle palatability. Feedlot heifers (n = 96) were administered one of six implant regimens to characterize their effect on in vitro amino acid uptake and protein degradation. Treatments consisted of: 1) a nonimplanted control (NI/NI); 2) no implant on d 1 and Revalor-H administered on d 84 of the experiment (NI/Rev); 3) Revalor-H on d 1, but no implant given at d 84 (Rev/NI); 4) Revalor-H administered on d 1 and d 84 (Rev/Rev); 5) Revalor-IH administered on d 1 and Revalor-H at d 84 (RIH/Rev); and 6) Synovex-H given at d 1 and Revalor-H administered at d 84 (Syn/Rev). Blood and longissimus lumborum muscle were collected 20 min postmortem, and serum and muscle extracts were incubated with primary bovine muscle cells. Implant treatments had minimal effects on shear force and sensory traits; however, steaks from Rev/Rev heifers were 0.31 kg more tender (P < 0.05) than steaks from NI/NI heifers. Serum protein synthesis and degradation were not affected (P > 0.10) by any implant treatment. When primary bovine muscle cells were treated with muscle extract, amino acid uptake was greater for heifers implanted with Rev/ Rev than for the average of all other treatments (P < 0.01). The Rev/Rev implant regimen also increased (P < 0.05) amino acid uptake compared with heifers treated with RIH/Rev, Syn/Rev, NI/NI, NI/Rev, or Rev/NI. Cellular protein degradation of the muscle cell culture treated with muscle extract tended (P < 0.10) to be higher in NI/NI-treated cells compared with the average of all implant treatments. In addition, cells treated with muscle extract from heifers implanted with Rev/Rev had lower (P < 0.05) protein degradation than the NI/NI control heifers. These results indicate that anabolic implant strategies can directly affect both muscle protein synthesis and degradation via effects that seem to be more autocrine than paracrine in nature.