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51.
52.
Abstract: Magnesium and the polyamines putrescine, spermidine, and spermine inhibited the activity of glutamate dehydrogenase in permeabilized rat brain mitochondria in a concentration-dependent manner. The inhibitory effect was observed on both the reductive amination of 2-oxoglutarate and oxidative deamination of glutamate, as well as in the presence and absence of ADP and leucine, the allosteric activators of the enzyme. Kinetic studies at various concentrations of substrates showed that inhibition by magnesium and spermine was very pronounced at 2-oxoglutarate concentrations less than 0.5 m M and NADH levels less than 0.08 m M . The presence of the former compounds also accentuated the inhibitory effect of high concentrations of 2-oxoglutarate (>2.0 m M ) and NADH (>0.32 m M ). Addition of magnesium and spermine to suspensions of synaptosomes decreased the amount of ammonia produced from glutamate. It is suggested that polyamines and magnesium, normal constituents of mammalian brain, are responsible, at least in part, for the low glutamate dehydrogenase activity in vivo. 相似文献
53.
Julie Y. H. Chan Hsing-Fei Tsai Terry B. J. Kuo Samuel H. H. Chan 《Regulatory peptides》1994,50(3):247-257
We evaluated possible modulation by angiotensin III (AIII) of the interactive effect of noxious stimuli and elevation in systemic arterial pressure on the responsiveness of neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Combined extracellular single-neuron recording and microiontophoresis were carried out on male, adult Sprague-Dawley rats anesthetized with pentobarbital sodium. The responsiveness of NRGC neurons to nociception (tail clamp) and/or transient hypertension elicited by phenylephrine (5 μg/kg, i.v.), in the absence or presence of AIII, was used as the experimental index. Microiontophoretic application of the heptapeptide suppressed the responses of spontaneously active NRGC neurons to individually delivered nociception or hypertension. Interestingly, the preferential reduction in responsiveness to tail clamp upon simultaneous elevation in arterial pressure was reversed to one that favored nociception in the presence of AIII. These actions of the heptapeptide appeared to be receptor-specific, since they were discernibly blocked by its selective antagonist, Ile7-angiotensin III. Our results reveal that neuropeptides such as AIII may differentially modulate neuronal responsiveness according to the prevailing physiologic input(s) to the central nervous system of the animal. 相似文献
54.
UDP-glucose dehydrogenase from bovine liver: primary structure and relationship to other dehydrogenases. 总被引:7,自引:0,他引:7 下载免费PDF全文
J. Hempel J. Perozich H. Romovacek A. Hinich I. Kuo D. S. Feingold 《Protein science : a publication of the Protein Society》1994,3(7):1074-1080
The primary structure of bovine liver UDP-glucose dehydrogenase (UDPGDH), a hexameric, NAD(+)-linked enzyme, has been determined at the protein level. The 52-kDa subunits are composed of 468 amino acid residues, with a free N-terminus and a Ser/Asn microhetergeneity at one position. The sequence shares 29.6% positional identity with GDP-mannose dehydrogenase from Pseudomonas, confirming a similarity earlier noted between active site peptides. This degree of similarity is comparable to the 31.1% identity vs. the UDPGDH from type A Streptococcus. Database searching also revealed similarities to a hypothetical sequence from Salmonella typhimurium and to "UDP-N-acetyl-mannosaminuronic acid dehydrogenase" from Escherichia coli. Pairwise identities between bovine UDPGDH and each of these sequences were all in the range of approximately 26-34%. Multiple alignment of all 5 sequences indicates common ancestry for these 4-electron-transferring enzymes. There are 27 strictly conserved residues, including a cysteine residue at position 275, earlier identified by chemical modification as the expected catalytic residue of the second half-reaction (conversion of UDP-aldehydoglucose to UDP-glucuronic acid), and 2 lysine residues, at positions 219 and 338, one of which may be the expected catalytic residue for the first half-reaction (conversion of UDP-glucose to UDP-aldehydoglucose). A GXGXXG pattern characteristic of the coenzyme-binding fold is found at positions 11-16, close to the N-terminus as with "short-chain" alcohol dehydrogenases.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
55.
Relationship between receptor/ligand binding affinity and adhesion strength. 总被引:10,自引:7,他引:3 下载免费PDF全文
Receptor-mediated cell adhesion is a central phenomenon in many physiological and biotechnological processes. Mechanical strength of adhesion is generally presumed to be related to chemical affinity of receptor/ligand bonds, but no experimental study has been previously directed toward this issue. Here we investigate the dependence of receptor/ligand adhesion strength on bond affinity using a radial fluid flow chamber assay to measure the force needed to detach polystyrene beads covalently coated with immunoglobulin G from glass surfaces covalently coated with protein A. A spectrum of animal species sources for immunoglobulin G permits examination of three decades of protein A/immunoglobulin G binding affinity. Our results for this model system demonstrate that adhesion strength varies with the logarithm of the binding affinity, consistent with a prediction from the theoretical model by Dembo et al. (Dembo, M., D.C. Torney, K. Saxman, and D. Hammer. 1988. Proc. R. Soc. Lond. Ser. B 234:55-83). 相似文献
56.
Fu-Chou Cheng Jon-Son Kuo Wen-Ho Chang Dong-Juiing Juang Ying Shih Jeng-Shiow Lai 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1993,617(2)
The simultaneous measurement of homovanillic acid, 3,4-dihydroxyphenylacetic acid, serotonin and 5-hydroxyindoleacetic acid in human plasma by an ultrafiltration and microbore high-performance liquid chromatography—electrochemical detection technique is established. Conventional preparation of blood is very tedious and time-consuming, but isocratic separation of the analytes in plasma ultrafiltrates using a microbore column could be achieved within 10 min. Hence, theoretically, over 140 analyses can be performed in a working day. The detection limit (signal-to-noise ratio = 3) of this method is about 0.1–0.5 pg per injection for all analytes. The required volume of plasma samples can be less than 100 μl. Hence, blood loss is minimal, especially in repeated blood sampling. This rapid, simple and sensitive method can, therefore, be used as a routine clinical tool in the simultaneous measurement of plasma homovanillic acid, 3,4-dihydroxyphenylacetic acid, serotonin and 5-hydroxyindoleacetic acid. 相似文献
57.
L-缬氨酸作为一种支链氨基酸,广泛应用于医药和饲料等领域。本研究借助多种代谢工程策略相结合的方法,构建了生产L-缬氨酸的微生物细胞工厂,实现了L-缬氨酸的高效生产。首先,通过增强糖酵解途径、减弱副产物代谢途径相结合的方式,强化了L-缬氨酸合成前体丙酮酸的供给;其次,针对L-缬氨酸合成路径关键酶—乙酰羟酸合酶进行定点突变,提高了菌株的抗反馈抑制能力,并利用启动子工程策略,优化了路径关键酶的基因表达水平;最后,利用辅因子工程策略,改变了乙酰羟酸还原异构酶和支链氨基酸转氨酶的辅因子偏好性,由偏好NADPH转变为偏好NADH,从而提高了L-缬氨酸的合成能力。在5L发酵罐中,最优谷氨酸棒杆菌工程菌株Corynebacterium glutamicum K020的L-缬氨酸产量、得率和生产强度分别达到了110g/L、0.51g/g和2.29 g/(L·h)。 相似文献
58.
Han-Yu Wang Yi-Ru Shen Yung-Chieh Tsai Shang-Rung Wu Chia-Yih Wang Pao-Lin Kuo 《Journal of cellular physiology》2023,238(3):597-609
Septin-based ring complexes maintain the sperm annulus. Defective annular structures are observed in the sperm of Sept12- and Sept4-null mice. In addition, sperm capacitation, a process required for proper fertilization, is inhibited in Sept4-null mice, implying that the sperm annulus might play a role in controlling sperm capacitation. Hence, we analyzed sperm capacitation of sperm obtained from SEPT12 Ser196 phosphomimetic (S196E), phosphorylation-deficient (S196A), and SEPT4-depleted mutant mice. Capacitation was reduced in the sperm of both the Sept12 S196E- and Sept12 S196A-knock-in mice. The protein levels of septins, namely, SEPT4 and SEPT12, were upregulated, and these proteins were concentrated in the sperm annulus during capacitation. Importantly, the expression of soluble adenylyl cyclase (sAC), a key enzyme that initiates capacitation, was upregulated, and sAC was recruited to the sperm annulus following capacitation stimulation. We further found that SEPT12, SEPT4, and sAC formed a complex and colocalized to the sperm annulus. Additionally, sAC expression was reduced and disappeared in the annulus of the SEPT12 S196E- and S196A-mutant mouse sperm. In the sperm of the SEPT4-knockout mice, sAC did not localize to the annulus. Thus, our data demonstrate that SEPT12 phosphorylation status and SEPT4 activity jointly regulate sAC protein levels and annular localization to induce sperm capacitation. 相似文献
59.
ML-1035, 4-amino-5-chloro-2-[2-(methylsulfinyl)ethoxy]-N-[2-(diethylamino)ethyl]benzamide, is a sulfoxide compound and a racemic gastroprokinetic agent with a chiral center at the sulfur atom. We have investigated the disposition kinetics of (R)-ML-1035 sulfoxide (R) and (S)-ML-1035 sulfoxide (S) after the single enantiomers and the racemic mixture were administered to rats in separate experiments. There was no noticeable chiral inversion after either enantiomer dose. Both enantiomers were rapidly absorbed. After dosing with enantiomers or with the racemate, the resulting plasma concentration-time curve of R was closely parallel to that of S in both intravenous and oral experiments, suggesting that the two enantiomers have approximately the same disposition kinetics. After intravenous enantiomer doses, only S underwent conversion to sulfide, suggesting that sulfidation in the liver is enantioselective. However, the enantioselective sulfidation after intravenous dosing did not introduce a difference in the global plasma disposition profiles between R and S, since the reduction reaction is a minor metabolic process. Other metabolic reactions such as sulfonation and mono-N-desethylations were not enantioselective. After oral administration, conversion to sulfide was observed for both enantioners, implicating the existence of a nonhepatic pathway in sulfidation. Administration of a prochiral sulfide dose was associated with an enantioselective sulfoxidation, in which the R/S concentration ratios increased as a function of time. In addition, enantiomeric interaction causing changes in pharmacokinetic parameters was observed after the oral racemate dose, while the interaction is negligible after an intravenous racemate dose, indicating a route dependency in enantiomeric interaction. © 1993 Wiley-Liss, Inc. 相似文献
60.
Yung-Chieh Tsai Tian-Ni Kuo Yu-Ying Chao Pei-Rong Lee Ruei-Ci Lin Xiao-Yi Xiao Bu-Miin Huang Chia-Yih Wang 《Journal of cellular biochemistry》2023,124(1):89-102
Testes control the development of male reproductive system. The testicular interstitial Leydig cells (Leydig cells) synthesize testosterone for promoting spermatogenesis and secondary sexual characteristics. Type A platelet-derived growth factor (PDGF-AA) is one of the most important growth factors in regulating Leydig cell growth and function. Knockout of PDGF-AA or its congenital receptor PDGFR-α leads to poor testicular development caused by reducing Leydig cell numbers, supporting PDGF-AA/PDGFR-α signaling regulates Leydig cell development. Primary cilium is a cellular antenna that functions as an integrative platform to transduce extracellular signaling for proper development and differentiation. Several receptors including PDGFR-α are observed on primary cilia for initiating signaling cascades in distinct cell types. Here we showed that PDGF-AA/PDGFR-α signaling promoted Leydig cells growth, migration, and invasion via primary cilia. Upon PDGF-AA treatment, AKT and ERK signaling were activated to regulate these cellular events. Interestingly, active AKT and ERK were detected around the base of primary cilia. Depletion of ciliary genes (IFT88 and CEP164) alleviated PDGF-AA-activated AKT and ERK, thus reducing Leydig cell growth, migration, and invasion. Thus, our study not only reveals the function of PDGF-AA/PDGFR-α signaling in maintaining testicular physiology but also uncovers the role of primary cilium and downstream signaling in regulating Leydig cell development. 相似文献