Effect of temperature on the saccharide composition obtained after alpha-amylolysis of starch

The hydrolysis of starch to low-molecular-weight products (normally characterised by their dextrose equivalent (DE), which is directly related to the number-average molecular mass) was studied at different temperatures. Amylopectin potato starch, lacking amylose, was selected because of its low tendency towards retrogradation at lower temperatures. Bacillus licheniformis alpha-amylase was added to 10% [w/w] gelatinised starch solutions. The hydrolysis experiments were done at 50, 70, and 90 degrees C. Samples were taken at defined DE values and these were analysed with respect to their saccharide composition. At the same DE the oligosaccharide composition depended on the hydrolysis temperature. This implies that at the same net number of bonds hydrolysed by the enzyme, the saccharide composition was different. The hydrolysis temperature also influenced the initial overall molecular-weight distribution. Higher temperatures led to a more homogenous molecular weight distribution. Similar effects were observed for alpha-amylases from other microbial sources such as Bacillus amyloliquefaciens and Bacillus stearothermophilus. Varying the pH (5.1, 6.2, and 7.6) at 70 degrees C did not significantly influence the saccharide composition obtained during B. licheniformis alpha-amylase hydrolysis. The underlying mechanisms for B. licheniformis alpha-amylase were studied using pure linear oligosaccharides, ranging from maltotriose to maltoheptaose as substrates. Activation energies for the hydrolysis of individual oligosaccharides were calculated from Arrhenius plots at 60, 70, 80, and 90 degrees C. Oligosaccharides with a degree of polymerisation exceeding that of the substrate could be detected. The contribution of these oligosaccharides increased as the degree of polymerisation of the substrate decreased and the temperature of hydrolysis increased. The product specificity decreased with increasing temperature of hydrolysis, which led to a more equal distribution between the possible products formed. Calculations with the subsite map as determined for the closely related alpha-amylase from B. amyloliquefaciens reconfirmed this finding of a decreased substrate specificity with increased temperature of hydrolysis. Copyright 1999 John Wiley & Sons, Inc.     

Mechanism of inhibition of porcine leukocyte 12-lipoxygenase by the isoform-specific inhibitor 4-(2-oxapentadeca-4-yne)phenylpropanoic acid

The mechanism of inhibition of porcine leukocyte 12-lipoxygenase by 4-(2-oxapentadeca-4-yne)phenylpropanoic acid (OPP) was investigated. This compound is selective for the leukocyte form of the 12-lipoxygenase and inhibits the purified recombinant enzyme with an IC(50) value of approximately 2 microM. OPP induced a concentration-dependent lag phase in the oxygenation of arachidonic acid and decreased the maximal rate of reaction. Addition of the fatty acid hydroperoxide 13(S)-hydroperoxyoctadecadienoic acid (13-HPODE) to the reaction greatly reduced the OPP-induced lag. Lineweaver-Burk analysis of the effect of OPP on 12-lipoxygenase kinetics with arachidonic acid indicated that it was a mixed-type inhibitor. OPP was not metabolized by 12-lipoxygenase as evidenced by its quantitative recovery from incubations with stoichiometric amounts of enzyme and 13-HPODE or arachidonic acid. OPP inhibited the pseudoperoxidase activity of the enzyme with 13-HPODE and the reducing agent, BWA137C. Lineweaver-Burk analysis of the effect of OPP on pseudoperoxidase kinetics suggested that OPP was competitive with 13-HPODE. Single-turnover experiments indicated that OPP inhibited the reduction of 13-HPODE by a stoichiometric amount of ferrous 12-lipoxygenase. Addition of 13-HPODE shortened the OPP-induced lag phase but did not affect the maximal rate of enzyme activity. In addition, OPP had no effect on total product formation in either the presence or the absence of 5 microM 13-HPODE when the reaction was allowed to go to completion. All of these observations are consistent with a model for inhibition of 12-lipoxygenase activity in which OPP slows the oxidation of the inactive ferrous enzyme to the active ferric enzyme and competes with arachidonic acid for the ferric enzyme.     

Bombesin activates MAP kinase in non-small cell lung cancer cells

The effects of bombesin (BB) on mitogen activated protein (MAP) kinase were investigated using non-small cell lung cancer (NSCLC) cells. By Western blot, both 42 and 44 kDalton forms of MAP kinase were present in NCI-H1299 and NCI-H838 cells. Addition of BB to NCI-H1299 cells resulted in phosphorylation of the MAP kinase substrate myelin basic protein (MBP). Phosphorylation of MBP was maximal 6 min after the addition of 10 nM BB to NCI-H1299 cells. Addition of gastrin releasing peptide (GRP) or GRP14-27 but not GRP1-16 to NCI-H 1299 cells caused MBP phosphorylation. The effects of BB were inhibited by BW2258U89, a BB receptor antagonist, and PD98059, a MAP kinase kinase inhibitor. Also, PD98059 inhibited the clonal growth of NCI-H1299 cells. These data suggest that MAP kinase may be an important regulatory enzyme in NSCLC.     

Regulation of primary spinal neuron lineages after deletion of a major progenitor

Vertebrate embryos are able to reconstitute the body plan when early blastomeres are deleted, but it is not known whether this is accomplished by cells local to the lesion or by a readjustment of the entire pattern of the embryo. We distinguished between these two possibilities by studying which embryonic cells change primary spinal neuronal fates after deletion of a major spinal cord progenitor. After ablation of the V1.2 blastomere of the 16-cell Xenopus embryo, the spinal cord contained normal numbers of Rohon-Beard neurons and primary motoneurons, indicating that the remaining blastomeres numerically reconstituted these populations. Using lineage-tracing techniques we revealed a global response: 10 out of the 15 remaining blastomeres significantly changed the number of one or both neuronal types they produced. This widespread response indicates that position in the early embryo plays an important role in regulating the production of primary spinal neurons. However, not all cells are influenced solely by position; a vegetal cell transplanted into the position of the deleted V1.2 did not take on the neuronal fate of its new position. Thus, restitution of pattern relies on a combination of positional cues and intrinsic fate restrictions.     

Expression of <Emphasis Type="Italic">PEG11</Emphasis> and <Emphasis Type="Italic">PEG11AS</Emphasis> transcripts in normal and callipyge sheep

Background  

The callipyge mutation is located within an imprinted gene cluster on ovine chromosome 18. The callipyge trait exhibits polar overdominant inheritance due to the fact that only heterozygotes inheriting a mutant paternal allele (paternal heterozygotes) have a phenotype of muscle hypertrophy, reduced fat and a more compact skeleton. The mutation is a single A to G transition in an intergenic region that results in the increased expression of several genes within the imprinted cluster without changing their parent-of-origin allele-specific expression.     

Carbon monoxide exposure in rat heart: glutathione depletion is prevented by antioxidants

Rat hearts were perfused for 15min with buffer equilibrated with 0.01% or 0.05% CO. The buffer was equilibrated with 21% O(2) throughout. The ventricular glutathione content decreased by 76% and 84%, 90min post-exposure to 0.01% and 0.05% CO, respectively, compared with 0% CO controls (0.45+/-0.01 micromol/g wet tissue; +/-SEM, n=3). Both reduced and oxidised glutathione contributed to this decline. When ascorbate and Trolox C were included during exposure to 0.05% CO the glutathione pool was partly protected; here the glutathione decrease was 46%. In most hearts additional creatine kinase activity in the perfusate indicated minor tissue injury occurring immediately after the start and/or about 10min after the end of exposure to 0.01% CO or 0.05% CO. Ventricle lactate levels were unaffected by exposure to 0.01% CO. This evidence supports a role for oxidative stress in CO cardiotoxicity.