Interactions of chloride and amiloride with the renal Na+/H/ antiporter

Amiloride is a reversible inhibitor of the Na+/H+ antiporter which acts at the external aspect of the transport system. The kinetics of inhibition of the Na+/H+ antiporter with amiloride have been controversial, with the usual finding of simple competitive inhibition, but with other reports of mixed and noncompetitive inhibition of the transporter by amiloride. The present experiments demonstrate that the chloride content of the external transport buffer affects the kinetics of amiloride inhibition. Either simple competitive or mixed inhibition by amiloride was observed in the same vesicle preparations depending on the presence of chloride or gluconate in the buffer. The effect of chloride on the inhibitory effect of amiloride was dependent on the concentration of chloride and amiloride. Similar effects were observed with more potent analogues of amiloride. These findings suggest that the external aspect of the antiporter has a site or sites at which the inhibitory effects of amiloride on the Na+/H+ antiporter can be modified by chloride, even though chloride has only slight effects on the kinetics of the Na+/H+ antiporter in the absence of amiloride.     

Clearance of rat C-reactive protein in vivo and by perfused liver.

The clearance in vivo of rat C-reactive protein (CRP) was studied: (i) in the whole animal and (ii) by using a rat liver perfusion system. Rat CRP is a glycosylated serum protein containing a complex-type biantennary carbohydrate structure on each of its five subunits. The half-life of rat asialo CRP was approximately 5 min. More than 75% of the radioactivity associated with rat asialo CRP and asialo alpha 1-acid glycoprotein (AGP) was recovered in the liver. A small amount of radioactivity (0.8%) associated with rat CRP and rat asialo CRP was found in the lungs. Competitive inhibition of the clearance of 125I-labelled rat asialo CRP from the circulation by asialo AGP was dose dependent, and resulted in a corresponding decrease in the recovery of radioactivity associated with rat asialo CRP in the liver. This indicated that asialo AGP and rat asialo CRP were cleared by the hepatic asialoglycoprotein receptor. This observation was confirmed when the clearance of rat asialo CRP was studied using a rat liver perfusion system. Using this system, the clearance of rat asialo CRP and asialo AGP from the perfusate was inhibited by N-acetylgalactosamine, but not by phosphorylcholine, a ligand through which most of the CRP reactions are mediated. This study provides an example of a circulating serum glycoprotein containing a biantennary carbohydrate structure that is cleared by the asialoglycoprotein receptor.     

BJ-HCC-20, a potential novel cancer-testis antigen.

In an effort to identify novel Cancer-Testis genes, we analyzed the sequence in the q26-28 region of human X chromosome by several on-line tools. The candidate sequences were then confirmed by experiments. We have obtained a novel Cancer-Testis gene, BJ-HCC-20. In vivo, it was found to have two isoforms. In samples of liver, colon, gastric and lung cancer tested, the expression frequency of BJ-HCC-20 is 25%, 17%, 21% and 15%, respectively. Full-length cDNAs of both BJ-HCC-20 isoforms were isolated and their gene structures and promoter regions were characterized. BJ-HCC-20 might have implications in theoretical and practical tumor biology.     

Hidden smectic properties of a chiral side-chain co-oligomer

We recently showed that a side-chain industrial co-oligosiloxane presents a quenchable enlarged blue phase behaviour at the cholesteric-isotropic phase transition. In this paper, we present the results of a structural study based on X-ray diffraction, differential scanning calorimetry and optical measurements. In particular, the smectic A organisation is demonstrated in the lower temperature domain, which was hitherto understood as a cholesteric phase. A structural model for this phase is proposed on the basis of the analysis of the anisotropic scattering of stretched fibers. Our results also suggest that the observed glass transition is indeed a rather complex phenomenon, which seems to involve not only the freezing of the main chains, but also smectic correlations at the side-chain level. Moreover, the calorimetric study indicates that, notwithstanding the conservation of the processed film's optical properties, low kinetic reorganisations occur at room temperature.     

广东汉族健康人载脂蛋白AⅠ-CⅢl-AⅣ基因簇DNA多态性及其单倍型分布

本文研究了中国广东汉族健康人群apoAI-CⅢ-AIV基因簇DNA限制性内切酶PstI、SstI和EcoRI片段长度多态性。其中等位基因P_1,P_2,S_1,S_2,R_1和R_2的频率分别为0.98,0.02,0.96,0.04,0.90和0.10。经卡方检验符合Hardy-Weinbery氏遗传平衡,与其他种族比较,本文结果显示中国广东汉族人P_2等位基因频率低于日本人、亚洲印第安人和高加索人,S_2等位基因频率低于日本人、菲律宾人、沙特阿拉伯人和亚洲印第安人,而与高加索人相近,R_2等位基因频率稍高于高加索人。不同种族间apoAI-CⅢ-AIV基因簇DNA多态频率无疑存在差异,这种差异可能是由于遗传漂变和自然选择单独或联合作用所致。对P_1、P_2,S_1、S_2和R_1、R_2构成的单倍型和连锁平衡程度进行了分析,结果显示这些单倍型处于连锁不平衡状态。     

Comparison of the enzymatic behavior of high molecular weight and free lysyl-tRNA synthetase from rat liver: kinetic analysis of lysylation of tRNA

Lysyl-tRNA synthetase occurs in the high molecular weight form in rat liver. The high molecular weight lysyl-tRNA synthetase has been previously demonstrated to exist as multienzyme complexes of aminoacyl-tRNA synthetases. The multienzyme complexes can be dissociated by hydrophobic interaction chromatography and yield fully active, free lysyl-tRNA synthetase. The free form is found to be twice as active as the complexed form in lysylation. Bisubstrate and product inhibition kinetics of lysylation are systematically carried out for highly purified free lysyl-tRNA synthetase and the 18 S synthetase complex. Surprisingly, the two enzyme forms exhibit distinctly different kinetic patterns in bisubstrate and product inhibition kinetics under identical conditions. The 18 S synthetase complex shows kinetic patterns consistent with an ordered bi uni uni bi ping pong mechanism, while the results of free lysyl-tRNA synthetase do not. We conclude that structural organization of lysyl-tRNA synthetase beyond quaternary structure of proteins may alter the enzyme behavior.