Gating of inward rectifier K+ channels by proton-mediated interactions of N- and C-terminal domains

Ion channels play an important role in cellular functions, and specific cellular activity can be produced by gating them. One important gating mechanism is produced by intra- or extracellular ligands. Although the ligand-mediated channel gating is an important cellular process, the relationship between ligand binding and channel gating is not well understood. It is possible that ligands are involved in the interactions of different protein domains of the channel leading to opening or closing. To test this hypothesis, we studied the gating of Kir2.3 (HIR) by intracellular protons. Our results showed that hypercapnia or intracellular acidification strongly inhibited these channels. This effect relied on both the N and C termini. The CO(2)/pH sensitivities were abolished or compromised when one of the intracellular termini was replaced. Using purified N- and C-terminal peptides, we found that the N and C termini bound to each other in vitro. Although their binding was weak at pH 7.4, stronger binding was seen at pH 6.6. Two short sequences in the N and C termini were found to be critical for the N/C-terminal interaction. Interestingly, there was no titratable residue in these motifs. To identify the potential protonation sites, we systematically mutated most histidine residues in the intracellular N and C termini. We found that mutations of several histidine residues in the C but not the N terminus had a major effect on channel sensitivities to CO(2) and pH(i). These results suggest that at acidic pH, protons appear to interact with the C-terminal histidine residues and present the C terminus to the N terminus. Consequentially, these two intracellular termini bound to each other through two short motifs and closed the channel. Thus, a novel mechanism for K(+) channel gating is demonstrated, which involves the N- and C-terminal interaction with protons as the mediator.     

籼粳亚种间杂交稻米脂肪含量的遗传分析

用包括基因型×环境互作效应的种子性状遗传模型,研究了籼粳亚种间杂交稻米脂肪含量的遗传特性,结果表明：在籼粳杂种中,脂肪含量的遗传表达主要受控于种子直接加性效应和母体加性效应,以前者为主．基因型X环境互作主要表现为显性（包括直接显性和母体显性）X环境以及细胞质X环境工作．直接近传率和母体遗传率都极显著．此外,根据遗传效应预测值对供试条本的利用价值作了评价．     

绢丝丽蚌胚胎发育的研究

绢丝丽蚌卵为均黄卵,爱精卵在雌蚌外鳃中进行胚胎发育,其卵裂为不等完全卵裂。在秋季自然常湿（水温变幅为２４－８℃）时,胚胎发育历时５１ｄ,经过卵裂期、原肠期,发育为具有透明原壳、过钩、闭壳肌丝、内足丝、刚毛和外足丝的成熟钩介幼虫。胚胎发育的不同时期与外鳃特征具相关性。     

Biodiesel production from high acid value waste frying oil catalyzed by superacid heteropolyacid

Transesterification of waste cooking oil with high acid value and high water contents using heteropolyacid H3PW12O40 x 6H2O (PW12) as catalyst was investigated. The hexahydrate form of PW(12) was found to be the most promising catalyst which exhibited highest ester yield 87% for transesterification of waste cooking oil and ester yield 97% for esterification of long-chain palmitic acid, respectively. The PW12 acid catalyst shows higher activity under the optimized reaction conditions compared with conventional homogeneous catalyst sulfuric acid, and can easily be separated from the products by distillation of the excess methanol and can be reused more times. The most important feature of this catalyst is that the catalytic activity is not affected by the content of free fatty acids (FFAs) and the content of water in the waste cooking oil and the transesterification can occur at a lower temperature (65 degrees C), a lower methanol oil ratio (70:1) and be finished within a shorter time. The results illustrate that PW12 acid is an excellent water-tolerant and environmentally benign acid catalyst for production of biodiesel from waste cooking oil.