Molecular dynamics simulation of oligosaccharides containing N-acetyl neuraminic acid

αD -N-acetyl neuraminic acid (Neu5Ac, sialic acid) is a commonly occurring carbohydrate residue in various cell surface glycolipids and glycoproteins. This residue is linked terminally or internally to Gal residues via an α(2 → 3) or α(2 → 6) linkage. In the cell surface receptor, sialyl-Lewis^X, a terminal α(2 → 3) linkage is present. Previous studies from our laboratory have shown that in solution Lewis^X adopts a relatively rigid structure. In order to model the Neu5Ac residue, vacuum molecular dynamics of this monosaccharide were compared with simulations that explicitly include solvent water. The dynamical average of the monosaccharide conformation obtained from the two simulations was similar. Vacuum calculations for the disaccharide Neu5Ac α(2 → 3) Gal β-O-methyl show that a number of low energy minima are accessible to this disaccharide. Molecular dynamics simulations starting from the low energy minima show conformational transitions with a time scale of 10–50 ps among several of the minima while large barriers between other minima prevent transitions on the time scale studied. Simulations of this disaccharide in the presence of solvent show fewer conformational transitions, illustrating a dampening effect of the solvent that has been observed in some other studies. Our results are most consistent with an equilibrium among multiple conformations for the Neu5Ac α(2 → 3) Gal β linkage. © 1994 John Wiley & Sons, Inc.     

Simultaneous production and partition of chitinase during growth of Serratia marcescens in an aqueous two-phase system

Summary Partition and production of the extracellular chitinase from Serratia marcescens were studied in PEG/dextran aqueous two-phase systems. The enzyme partitions into the bottom phase and the cells segregate into the top phase. The best system is 2% (w/v) PEG 20000 and 5% (w/v) dextran T500. The cell growth and enzyme production kinetics are similar in the aqueous two-phase system and in the polymer-free reference system. However, the maximum enzyme concentration in the former system is 1.5 times that in the latter one.     

Hydraulic properties of sphagnum peat moss and tuff (scoria) and their potential effects on water availability

The importance of macrostructure to root growth of ryegrass (L. perenne) seedlings sown on the soil surface was studied in two soils in which the macrostructure had resulted mainly from root growth and macro-faunal activity. Sets of paired soil cores were used, one of each pair undisturbed and the other ground and repacked to the field bulk density. Undisturbed and repacked soils were first compared at equal water potentials in the range −1.9 to −300 kPa. At equal water potential, the undisturbed soil always had the greater strength (penetration resistance), and root growth was always greater in the repacked soil with no macrostructure than it was in the soil with macrostructure intact. At equal high strength (low water potentials) it appeared that root growth was better when soils were structured. When strength was low (high water potentials), root growth was better in the unstructured soil. Soils were then compared during drying cycles over 21 days. The average rate at which roots grew to a depth of 60 mm, and also the final percentage of plants with a root reaching 60 mm depth, was greatest in repacked soils without macrostructure. The species of vegetation growing in the soil before the experiment affected root growth in undisturbed soil; growth was slower where annual grasses and white clover had grown compared with soil which had supported a perennial grass. It appears that relatively few roots locate and grow in the macrostructure. Other roots grow in the matrix, if it is soft enough to be deformed by roots. Roots in the matrix of a structured soil grow more slowly than roots in structureless soil of equal bulk density and water potential. The development of macrostructure in an otherwise structureless soil, of the type studied, is of no advantage to most roots. However, once a macrostructure has developed, the few roots locating suitable macropores are able to grow at low water potential when soil strength is high. The importance of macrostructure to establishing seedlings in the field lies in rapid penetration of at least a few roots to a depth that escapes surface drying during seasonal drought. ei]{gnB E}{fnClothier}     

Salicylic acid inhibits the biosynthesis of ethylene in detached rice leaves

The effects of salicylic acid (SA) on ethylene biosynthesis in detached rice leaves were investigated. SA at pH 3.5 effectively inhibited ethylene production within 2 h of its application. It inhibited the conversion of ACC to ethylene, but did not affect the levels of ACC and conjugated ACC. Thus, the inhibitory effect of SA resulted from the inhibition of both synthesis of ACC and the conversion of ACC to ethylene.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene-forming enzyme - SA salicylic acid     

Effect of genetic background on growth of mice hemizygous for wild-type or dwarf mutated bovine growth hormone transgenes

The effects of a high-growth genetic background on the growth of mice hemizygous for one of two growth hormone transgenes were examined. Male mice hemizygous for wild-type (W) and dwarf mutant (M) bovine growth hormone (bGH) transgenes were crossed with females of a high-growth selected (S) and control (C) line as follows: W x S, W x C, M x S and M x C. Body weights of progeny were recorded weekly from 2 to 10 weeks of age. F₁ progeny were classified as carriers (P) or non-carriers (N) of the transgene by assaying tail DNA for bGH using the polymerase chain reaction and agarose gel electrophoresis. A deficiency in the number of f₁ progeny carrying the W (P<0.05) and M (P<0.01) bGH transgene was most likely due to differential prenatal and early postnatal mortality. Bodyweight means of wild-type transgenic mice were larger (P < 0.05) than those of non-transgenic littermates by 3 weeks of age in a C background in contrast to 5 weeks in S. The wild-type bGH transgene increased adult body weights more in the C (155%) than in the S (136%) background, indicating transgene expression by selection background interaction (P < 0.05). However, the growth response to the wild-type transgene in the S background was still large. The dwarf mutant transgene had a greater effect on growth reduction in the S (70%) than in the C (84%) background, thus causing transgene expression by selection background interaction (P < 0.05). Gender by wild-type transgene effect interactions (P < 0.001) for adult body weight were caused by the transgene reducing the gender difference for body weight in C and eliminating it in S. The dwarf mutant caused a larger negative effect on growth in males than in females, resulting in a gender by dwarf mutant transgene interaction (P < 0.001) for adult body weights. Results indicate that the effect of a GH transgene on growth can be affected both by a high-growth genetic background and the gender of progeny.     

不同磷脂和糖脂对莱氏衣原体膜上Mg~（2＋）－ATPase活性的影响

莱氏衣原体膜上Ｍｇ~（２＋）－ＡＴＰａｓｅ用ＤＯＣ溶解后,经Ｓｅｐｈａｒｏｓｅ－６Ｂ和ＤＥＡＥ－ＣｅｌｌｕｌｏｓｅＤＥ－５２离子交换柱,得到了部分纯化的Ｍｇ~（２＋）ＡＴＰａｓｅ,并将此ＡＴＰａｓｅ与不同极性头部的磷脂和膜糖脂重组,研究了不同的极性头部的磷脂和膜糖脂对ＡＴＰａｓｅ活性的影响。此酶的活性不依赖酸性磷脂,ＰＧ、ＤＰＧ、大豆磷脂等明显抑制酶活性,中性磷脂ＤＭＰＣ、ＰＥ、ＰＣ则能增加酶活性,其中尤以非双层脂ＰＥ的作用最为明显。从莱氏衣原体膜上提取的糖脂（ＭＧＤＧ,ＤＧＤＧ）单独和ＡＴＰａｓｅ重组时,酶活性增加并不明显,当ＭＧＤＧ和ＤＧＤＧ以等比例混合时,能大大地增加酶活性。这表明Ｍｇ~（２＋）－ＡＴＰａｓｅ的活性很大程度上与磷脂的表面电荷及磷脂的组成相关。     

Age-Dependent Impairment of Mitochondrial Function in Primate Brain

Abstract: It has been hypothesized that some of the functional impairments associated with aging are the result of increasing oxidative damage to mitochondrial DNA that produces defects in oxidative phosphorylation. To test this hypothesis, we examined the enzymes that catalyze oxidative phosphorylation in crude mitochondrial preparations from frontoparietal cortex of 20 rhesus monkeys (5-34 years old). Samples were assayed for complex I, complex II-III, complex IV, complex V, and citrate synthase activities. When enzyme activities were corrected for citrate synthase activities (to account for variable degrees of mitochondrial enrichment), linear regression analysis demonstrated a significant negative correlation of the activities of complex I (p < 0.002) and complex IV (p < 0.03) with age but no significant change in complex II-III or complex V activities. Relative to animals 6.9 ± 0.9 years old (n = 7), the citrate synthase-corrected activity of complex I was reduced by 17% in animals 22.5 ± 0.9 years old (n = 6) (p < 0.05) and by 22% in animals 30.7 ± 0.9 years old (n = 7) (p < 0.01). Similar age-related reductions in the activities of complexes I and IV were obtained when enzyme activities were corrected for complex II-III activity. These findings show an age-associated progressive impairment of mitochondrial complex I and complex IV activities in cerebral cortices of primates.     

Neutron structure factors of in-vivo deuterated amorphous protein C-phycocyanin

Neutron powder diffraction measurements of fully deuterated protein C-phycocyanin have been made at three temperatures, 295, 200, and 77 K, using dry and partially hydrated samples. The average coherent structure factors and the corresponding radial distribution functions d(r) are determined. The changes in d(r) functions observed in hydrated samples depend strongly on the level of hydration and most of these changes are due to water-protein interactions. At 0.365 gram D₂O per gram of protein, the water crystallized into hexagonal ice at 200 K and below, but at 0.175 gram D₂O per gram of protein, no crystallization of water was observed. At the higher hydration a peak appears in the radial distribution function which indicates that the average distance of the water molecule in the first hydration shell from the amino acid residues is 3.5 Å.