beta-Methyl-15-p-iodophenylpentadecanoic acid metabolism and kinetics in the isolated rat heart

The use of 15-p-iodophenyl-beta-methyl-pentadecanoic acid (beta Me-IPPA) as an indicator of long chain fatty acid (LCFA) utilization in nuclear medicine studies was evaluated in the isolated, perfused, working rat heart. Time courses of radioactivity (residue curves) were obtained following bolus injections of both beta Me-IPPA and its straight chain counterpart 15-p-iodophenyl-pentadecanoic acid (IPPA). IPPA kinetics clearly indicated flow independent impairment of fatty acid oxidation caused by the carnitine palmitoyltransferase I inhibitor 2[5(4-chlorophenyl)pentyl]oxirane-2-carboxylate (POCA). In contrast, beta Me-IPPA kinetics were insensitive to changes in fatty acid oxidation rate and net utilization of long chain fatty acid. Analysis of radiolabeled species in coronary effluent and heart homogenates showed the methylated fatty acid to be readily incorporated into complex lipids but a poor substrate for oxidation. POCA did not significantly alter metabolism of the tracer, suggesting that the tracer is poorly metabolized beyond beta Me-IPPA-CoA in the oxidative pathway.     

Comparison of 16-iodohexadecanoic acid (IHDA) and 15-p-iodophenylpentadecanoic acid (IPPA) metabolism and kinetics in the isolated rat heart

Time courses of radioactivity (residue curves) were obtained following bolus injection into working rat hearts of two 125I-labeled long chain fatty acids: 16-iodohexadecanoic acid (IHDA) and 15-p-iodophenylpentadecanoic acid (IPPA). Residue curves were analyzed in terms of a rapid vascular washout component, an early tissue clearance component, and a very slow late component. For IHDA and IPPA in control hearts, early myocardial clearance kinetics were rate limited by the diffusion of catabolites. Sensitivity of the kinetics to impaired fatty acid oxidation was examination by pretreatment of animals with 2[5(4-chlorophenyl)pentyl]oxirane-2-carboxylate (POCA). Decreased fatty acid oxidation was indicated in IHDA and IPPA residue curves by a decrease in the relative size of the early clearance component. Analysis of radiolabeled species in coronary effluent and heart homogenates showed that back diffusion of IPPA was slower than that of IHDA; this discrepancy was most apparent in POCA hearts. In vitro binding assays suggested higher tissue:albumin relative affinity for IPPA than for IHDA. Thus, IPPA early clearance kinetics were more closely related to the clearance of labeled catabolite(s) and were therefore more sensitive to the oxidation rate of long chain fatty acids.     

毛线柱苣苔化学成分的研究

从毛线柱苣苔(Rhynchotechum vestitum Hook.f.et Thoms.)根和茎中分得五种脂溶性成分,晶Ⅰ为β-谷甾醇(Ⅰ),晶Ⅱ为羽扇豆醇(lupeol,Ⅱ),其余三种为蒽醌化合物,晶Ⅲ和晶Ⅳ分别鉴定为甲基异茜草素-1-甲醚(rubiadin-1-methylether,Ⅲ)和甲基异茜草素°(rbuiadin,Ⅳ),晶V为一新化合物,经光谱分析初步推定其结构为1,6-二羟基-2-甲基-7,8-二甲氧基-9,10-蒽醌,命名为毛线柱苣苔蒽醌(rhynchotechol,Ⅴ)。     

仙鹤草根芽中新鞣花酸甙的结构研究

继前报从仙鹤草(Agrimonia pilosa Ledeb)根芽中分得(R)-(-)-仙鹤草酚B、伪绵马素、仙鹤草内酯-6-O-β-D-葡萄吡喃糖甙、反式对羟基肉桂酸酯、(2S,3S)-(-)-花旗松素-3-O-β-D-葡萄吡喃糖甙等后,又从其根芽中分得晶ⅩⅢ～ⅩⅥ。经理化性质,波谱数据,化学降解以及衍生物制备,将其中的一个新化合物确定为鞣花酸-4-O-β-D-木吡喃糖甙(ⅩⅤ),另外三个已知化合物分别鉴定为仙鹤草内酯(ⅩⅢ),委     

Structure and mechanism of proton transport through the transmembrane tetrameric M2 protein bundle of the influenza A virus

The M2 proton channel from influenza A virus is an essential protein that mediates transport of protons across the viral envelope. This protein has a single transmembrane helix, which tetramerizes into the active channel. At the heart of the conduction mechanism is the exchange of protons between the His37 imidazole moieties of M2 and waters confined to the M2 bundle interior. Protons are conducted as the total charge of the four His37 side chains passes through 2⁺ and 3⁺ with a pK_a near 6. A 1.65 Å resolution X-ray structure of the transmembrane protein (residues 25–46), crystallized at pH 6.5, reveals a pore that is lined by alternating layers of sidechains and well-ordered water clusters, which offer a pathway for proton conduction. The His37 residues form a box-like structure, bounded on either side by water clusters with well-ordered oxygen atoms at close distance. The conformation of the protein, which is intermediate between structures previously solved at higher and lower pH, suggests a mechanism by which conformational changes might facilitate asymmetric diffusion through the channel in the presence of a proton gradient. Moreover, protons diffusing through the channel need not be localized to a single His37 imidazole, but instead may be delocalized over the entire His-box and associated water clusters. Thus, the new crystal structure provides a possible unification of the discrete site versus continuum conduction models.