Changes in the form and ultrastructure of the smooth-muscle cells in the human aorta in prenatal ontogeny]

The shape of smooth muscle cells (SMC) was analysed using the phase contrast microscopy of cell suspensions obtained by alcohol-alkali dissociation, as well as the semithin sections prepared in perpendicular planes. The phenotype of SMC was analysed using transmission electron microscopy. The shape of SMC changes from preferentially round to preferentially spindle-like and stellate one during development. The differentiation of SMC is accompanied with the increase in the contractile apparatus content and in the decrease in the content of synthetic organelles.     

Investigation of mechanisms of interaction between inulinase from Kluyveromyces marxianus and the matrices of ion-exchange resins and fiber

It is established that ion exchange resins AV-17-2P, KU-2, AV-16-GS, AM 21A, IMAC-HP, PUROLITE and fiber VION KN-1 can be applied as carriers for inulinase immobilization. The analysis of IR spectra for an enzyme, carriers and heterogeneous enzyme preparations showed that inulinase binding to matrices of various carriers occurs in general through electrostatic interactions. It is assumed that the mechanisms of interaction between inulinase from Kluyveromyces marxianus and the matrices of cation and anion exchange polymers differ essentially from each other: different sites of protein molecule take part in adsorption that causes various conformational reorganizations in an enzyme molecule.     

Purification and some catalytic properties of phosphoglucomutase from maize leaves

Phosphoglucomutase (EC 2.7.5.1, PGM) was purified to homogeneity from maize (Zea mays L.) leaves. The enzyme had specific activity 11. 7 U/mg protein and molecular mass (determined by gel-chromatography) of 133 +/- 4 kD. The molecular mass of PGM subunits determined by SDS-electrophoresis was 66 +/- 3 kD. The enzyme had Km for glucose-1-phosphate and glucose-1,6-diphosphate of 20.0 +/- 0.9 and 16.0 +/- 0.8 &mgr;M, respectively. Concentrations of glucose-1-phosphate and glucose-1,6-diphosphate above 3 and 0.4 mM, respectively, cause substrate inhibition. The enzyme activity was maximal at pH 8.0 and temperature 35 degreesC. Magnesium ions activate the enzyme and manganese ions inhibit it. 3-Phosphoglycerate is an uncompetitive inhibitor of the enzyme (Ki = 1.22 +/- 0.05 mM). Fructose-6-phosphate, 6-phosphogluconate, and ADP activate PGM, whereas ATP, UTP, and AMP inhibit the enzyme. Citrate was also a potent inhibitor, inhibitory effects of isocitrate and cis-aconitate being less pronounced.     

Kinetic and allosteric properties of highly-purified, biosynthetic L-threonine dehydrogenase from brewer's yeast Saccharomyces carlsbergensis

Kinetic and allosteric propeties of highly purified "biosynthetic" L-threonine dehydratase from brewer's yeast S. carlbergensis were studied at three pH values, using L-threonine and L-serine as substrates. It was shown that the plot of the initial reaction rate (v) versus initial substrate concentrations ([S]0 pH 6.5 is hyperbolic (Km=5.0.10-2M), while these at pH 7.8 and 9.5 have a faintly pronounced sigmoidal shape with fast occurring saturation plateaus ([S]0.5= 1.0.10-2 and 0.9.10-2M, respectively). the ratios between L-threonine and L-serine dehydratation rates depend on pH. The kinetic properties and the dependence of substrate specificity on pH suggest that the enzyme molecule undergoes pH-induced (at pH 7.0) conformational changes. The determination of pK values of the enzyme functional groups involved in L-threonine binding demonstrated that these groups have pK is approximately equal to 7.5 and 9.5. The latter group was hypothetically identified as a epsilon-NH2-group of the lysine residue. High concentrations of the allosteric inhibitor (L-isoleucine) decrease the rates of L-threonine and L-serine dehydratation and induce the appearance (at pH 6.5) or increase (at pH 7.9 and 9.5) of homotropic cooperative interactions between the active sites in the course of L-threonine dehydratation. The enzyme inhibition by L-isoleucine increases with a decrease of L-threonine concentrations. Low L-isoleucine concentrations, as well as the enzyme activator (L-valine) stimulate the enzyme at non-saturating substrate concentrations (when L-threonine or L-serine are used as substrates) without normalization of (v) versus [S]0 plots. The maximal activation of the enzyme is observed at pHG 8.5--9.0. It is assumed that the molecule of "biosynthetic" L-threonine dehydratase from brewer's yeast contains two types of sites responsible for the effector binding, i.e., "activatory" and "inhibitory" ones.     

Kinetic-thermodynamic aspects of catalysis of polysaccharides by native end immobilized amylases

It was shown that covalent immobilization of 1.4-alpha-glucanohydrolase (glucoamylase) and 2.1-beta-D-fructanfructanohydrolase (inulase) on ionites leads to an increase in the activation energy Eact of hydrolysis of polysaccharides and a change in entalphy delta H as compared with native enzymes. During binding to the matrix, multipoint interactions of polypeptide chains with active groups take place, which are accompanied by an increase in the Michaelis constant KM, a decrease in the maximum rate of hydrolysis Vmax, and a substantial decrease in the constant of conformational transition L0. It was also shown that the kinetics of the hydrolysis of starch and inulin upon immobilization of glucoamylase and inulase on ionites does not correspond to the Michaelis-Menten equiation and is characterized by a shift of equilibrium from state R to state T.     

Age and chromosome nondisjunction]

The parental age in 77 families of Down syndrome (DS) children with the known origin of extra chromosome 21 and in 12 families of DS children resulting from de novo translocation (more probable than not in 2 meiotic division) was studied. It was shown that when nondisjunction occurred in the 1st meiotic division, both in oogenesis (n = 30) and spermatogenesis (n = 12), mean parental ages and age distributions were different from that of control (400 couples with normal children). The mean age and age distribution were found to differ from control when nondisjunction occurred in the 2nd meiotic division of oogenesis (n = 19). On the basis of our information and the previously published data, lack of the effect of parental age on chromosome segregation in the Ist meiosis may be inferred. It is chromatid disjunction in the 2nd meiosis which is more probably age-dependent. The reasons preventing elucidation of real associations are under debate.     

The Dutch N-cascade in the European perspective

The Netherlands is "well known" for its nitrogen problems; it has one of the highest reactive nitrogen (Nr) emission densities in the world. It is a small country at the delta of several large European rivers. Ever since the industrial revolution, there has been a growing excess of nutrients and related emissions into the atmosphere (ammonia, nitrogen oxides and nitrous oxide) and into groundwater and surface water (nitrate), leading to a large range of cascading environmental impacts. Vehicular traffic, sewage and animal husbandry are the main sources of oxidized and reduced forms of Nr. This paper provides an overview of the origin and fate of nitrogen in the Netherlands, the various reported impacts of nitrogen, the Dutch and European policies to reduce nitrogen emissions and related impacts. In addition, ways are presented to go forward to potentially solve the problems in a European perspective. Solutions include the improvement of nitrogen efficiencies in different systems, technological options and education.