Acrolein modifies and inhibits cytosolic aspartate aminotransferase

Acrolein is a reactive lipid peroxidation byproduct, which is found in ischemic tissue. We examined the effects of acrolein on cytosolic aspartate aminotransferase (cAAT), which is an enzyme that was previously shown to be inhibited by glycating agents. cAAT is thought to protect against ischemic injury. We observed that acrolein cross-linked cAAT subunits as evidenced by the presence of high molecular weight bands following SDS-PAGE. Acrolein-modified cAAT resisted thermal denaturation when compared with native cAAT. We also observed a decrease in intrinsic fluorescence (290 nm, ex; 380 nm, em). These observations are consistent with an acrolein-induced change in conformation that is more rigid and compact than native cAAT, suggesting that intramolecular cross-links occurred. Acrolein also inhibited activity, and the inhibition of enzyme activity correlated with the acrolein-induced formation of cAAT cross-links.     

Coupled pacing improves cardiac efficiency during acute atrial fibrillation with or without cardiac dysfunction

Coupled pacing (CP), a method for controlling ventricular rate during atrial fibrillation (AF), consists of a single electrical stimulation applied to the ventricles after each spontaneous activation. CP results in a mechanical contraction rate approximately one-half the rate during AF. Paired stimulation in which two electrical stimuli are delivered to the ventricles has also been proposed as a therapy for heart failure. Although paired stimulation enhances contractility, it greatly increases energy consumption. The primary hypothesis of the present study is that CP improves cardiac function during acute AF without a similar increase in energy consumption because of the reduced rate of ventricular contractions. In a canine model, CP was applied during four stages: sinus rhythm (SR), acute AF, cardiac dysfunction (CD), and AF in the presence of cardiac dysfunction. The rate of ventricular contraction decreased in all four stages as the result of CP. In addition, we determined the changes in external cardiac work, myocardial oxygen consumption, and myocardial efficiency in the each of four stages. CP partially reversed the effects of AF and CD on external cardiac work, whereas myocardial oxygen consumption increased only moderately. In all stages but SR, CP increased myocardial efficiency because of the marked increases in cardiac work compared with the moderate increases in total energy consumed. Thus this pacing therapy may be a viable therapy for patients with concurrent atrial fibrillation and heart failure.     

Evolution of arthropod hemocyanins and insect storage proteins (hexamerins)

Crustacean and cheliceratan hemocyanins (oxygen-transport proteins) and insect hexamerins (storage proteins) are homologous gene products, although the latter do not bind oxygen and do not possess the copper- binding histidines present in the hemocyanins. An alignment of 19 amino acid sequences of hemocyanin subunits and insect hexamerins was made, based on the conservation of elements of secondary structure observed in X-ray structures of two hemocyanin subunits. The alignment was analyzed using parsimony and neighbor-joining methods. Results provide strong indications for grouping together the sequences of the 2 crustacean hemocyanin subunits, the 5 cheliceratan hemocyanin subunits, and the 12 insect hexamerins. Within the insect clade, four methionine- rich proteins, four arylphorins, and two juvenile hormone-suppressible proteins from Lepidoptera, as well as two dipteran proteins, form four separate groups. In the absence of an outgroup sequence, it is not possible to present information about the ancestral state from which these proteins are derived. Although this family of proteins clearly consists of homologous gene products, there remain striking differences in gene organization and site of biosynthesis of the proteins within the cell. Because studies on 18S and 12S rRNA sequences indicate a rather close relationship between insects and crustaceans, we propose that hemocyanin is the ancestral arthropod protein and that insect hexamerins lost their copper-binding capability after divergence of the insects from the crustaceans.      

植物抗病基因工程进展(续)

植物抗病基因工程进展（续）洪剑明印莉萍邱泽生（首都师范大学生物系北京１０００３７）ＰＲＯＧＲＥＳＳＯＦＧＥＮＥＴＩＣＥＮＧＩＮＥＥＲＩＮＧＦＯＲＰＬＡＮＴＤＩＳＥＡＳＥＲＥＳＩＳＴＡＮＣＥＨＯＮＧＪｉａｎＭｉｎｇＹＩＮＬｉＰｉｎｇＱＩＵＺｅＳｈ...     

Population structure in the American oyster as inferred by nuclear gene genealogies

Multiple haplotypes from each of three nuclear loci were isolated and sequenced from geographic populations of the American oyster, Crassostrea virginica. In tests of alternative phylogeographic hypotheses for this species, nuclear gene genealogies constructed for these haplotypes were compared to one another, to a mitochondrial gene tree, and to patterns of allele frequency variation in nuclear restriction site polymorphisms (RFLPs) and allozymes. Oyster populations from the Atlantic versus the Gulf of Mexico are not reciprocally monophyletic in any of the nuclear gene trees, despite considerable genetic variation and despite large allele frequency differences previously reported in several other genetic assays. If these populations were separated vicariantly in the past, either insufficient time has elapsed for neutral lineage sorting to have achieved monophyly at most nuclear loci, or balancing selection may have inhibited lineage extinction, or secondary gene flow may have moved haplotypes between regions. These and other possibilities are examined in light of available genetic evidence, and it is concluded that no simple explanation can account for the great variety of population genetic patterns across loci displayed by American oysters. Regardless of the source of this heterogeneity, this study provides an empirical demonstration that different sequences of DNA within the same organismal pedigree can have quite different phylogeographic histories.      

Motional properties of a pentasaccharide containing a 2,6-branched mannose residue as studied by 13C nuclear spin relaxation

Summary ¹³C relaxation data obtained at three different magnetic fields, 9.4, 11.8 and 14.1 T, and at two temperatures, 303 and 318 K, are reported for the pentasaccharide p-trifluoroacetamidophenyl 2,6-di-O-[-d-galactopyranosyl-(14)-O-2-acetamido-2-deoxy--d-glucopyranosyl]-d-mannopyranoside. The pentasaccharide consists of two disaccharide units, attached at position 2 and 6 to the central mannopyranoside residue. The relaxation data were interpreted with the Lipari-Szabo model-free approach. For the central mannose residue in the molecule a high order parameter (S²=0.91) was found and the relaxation data could be interpreted with the truncated form of the Lipari-Szabo model. The motional behavior of the two 2-acetamido-2-deoxy-glucopyranoside residues was found to differ. The one attached at the primary hydroxylic position displayed more extensive local motion (S²=0.75–0.77) than the one attached at the secondary hydroxylic position (S²=0.83–0.85). More extensive local motion for the two outer galactopyranoside residues was found (S²=0.56–0.59), but no significant difference in motional behavior between the two residues could be observed. Analysis of the relaxation data for the exocyclic carbons confirmed the results for the rings. For the mannose C6, the same motional parameters as obtained for the substituting 2-acetamido-2-deoxy-glucopyranoside residue were found. The two exocyclic carbons on the 2-acetamido-2-deoxy-glucopyranoside residues showed more extensive local motion, with lower order parameters (S²=0.59–0.66).To whom correspondence should be addressed.     

Acute lesions of the ventromedial hypothalamus reduce sympathetic activation and thermogenic changes induced by PGE1

The aim of this experiment was to evaluate the effects of an intracerebroventricular (icv) injection of prostaglandin E1 (PGE₁) on the sympathetic activation and the thermogenic changes in rats with acute lesions of the ventromedial hypothalamus (VMH). Four groups of six Sprague-Dawley male rats were anesthetized with ethyl-urethane. The firing rate of the sympathetic nerves innervating the interscapular brown adipose tissue (IBAT) and the colonic and IBAT temperatures were monitored both before and after one of the following treatments: 1) VMH lesion plus icv injection of PGE₁ (500 ng); 2) VMH lesion plus icv injection of saline; 3) sham lesion plus icv injection of PGE₁; and 4) sham lesion plus icv injection of saline. PGE₁ induced an increase in the firing rate of IBAT nerves and the colonic and IBAT temperatures. These effects were reduced by VMH lesion. The findings indicate that acute lesions of the VMH reduce the effects of PGE₁ and seem to suggest a possible role played by the VMH in the control of the sympathetic activation and the thermogenic changes during PGE₁ hyperthermia.