Parent Substrate Research Articles

Stimulation of the glucuronidation of digitoxigenin-monodigitoxoside by liver homogenates from spironolactone-pretreated rats

Pretreatment of rats with spironolactone (SPL) produces an increased formation of the glucuronide conjugates of digitoxigenin-mono-digitoxoside (DMD) present in the bile after administration of digitoxin. For the digitoxin series of cardiac glycosides, DMD is the preferred substrate for in vitro conjugation with glucuronic acid by rat liver homogenates. The present experiments were performed to determine whether SPL pretreatment could produce an inceased glucuronidation of DMD by rat liver homogenates. Three different substrate concentrations (3, 30, and 100 nmol DMD/g of liver homogenate) were incubated under identical conditions with homogenates from control and SPL-pretreated rats. At 3.0-nmol. treatment with SPL produced a slight, but significant, increase in the production of aqueous alcohol-soluble metabolites of DMD by the experimental homogenates. With 30 nmol, treatment with SPL produced a 1.57-fold increase in the formation of aqueous alcohol-soluble metabolites of DMD. At 100 nmol, treatment with SPL produced a 3.44-fold increase in the formation of the aqueous alcohol-soluble metabolites of DMD. Treatment of these aqueous alcohol-soluble fractions (30-nmol substrate incubations only) with β-glucuronidase converted nearly 99% of the activity to a nonconjugate fraction. For both the control and the SPL-treated groups, greater than 92% of this nonconjugate fraction was determined by high-pressure liquid chromatography (HPLC) to be identical to the parent substrate (i.e., DMD). Thus, by selective enzyme treatment of the apparent conjugate and subsequent HPLC identification of the released products, the aqueous alcohol-soluble metabolites were identified as glucuronide conjugates of DMD. Pretreatment with spironolactone increased the rate of glucuronidation of DMD by rat liver homogenates.

Acquisition of substrate-specific parameters during the catalytic reaction of penicillinase.

The progress of the catalytic reaction of penicillinase (EC 3.5.2.6; penicillin amido-beta-lactamhydrolase) depends on the structure of the side-chain in derivatives of 6-aminopenicillanic acid (the parent substrate). Side-chains of one class promote the rate of the reaction and cause no deviation from the linear kinetics observed with the parent compound. By contrast, side-chains of the other class induce a time-dependent, reversible change in the parameters of the catalytic reaction. The rate decelerates considerably and then becomes constant; the decrease in kcat is accompanied by a corresponding decrease in Km. The initial parameters of the biphasic reaction, determined by stopped-flow spectrophotometry, approach those of the unsubstituted 6-aminopenicillanic acid. The final parameters, which are specific for each derivative, are not acquired when the native conformation of the enzyme is stabilized by homologous antibodies.

Pleistozäne Periglazialbildungen als Muttersubstrat der Böden in den Westkarpathen

The major part of the parent substrate of the soils in the West Karpathians is composed of sedimentary rocks. In the plains, loess sediments, eolian sand, and alluvial sediments dominate, while in the area with undulating topography, the weathering products of different rocks are transported by the process of solifluction displacement. For the classification of Pleistocene periglacial formations, different schemes by different authors (e.g., Priehausser, Schilling, Semmel etc.) have been proposed and we agree with the proposal of Schilling. The so-called singular sequence developed in the West Karpathians is as follows. 1. (1) The basic sequence consists of 1–3 layers (mainly solifluction debris) with a total thickness of 20–250 cm. 2. (2) The main sequence, usually 1 or 2 layers (mainly mud flows), is 30–140 cm thick. 3. (3) The covering sequence of solifluction debris is 10–80 cm thick. In many cases the combination of solifluction debris and the main mud flows is encountered. The covering sequence is relatively rare and is encountered only in extreme chemical rocks (quartz rock, dolomite). These layers mostly represent the soil horizons. In the upper layer, 1 or 2 soil horizons are developed. The layers of slope sediments at 700–1,200 m above sea level are very well developed. The soils at higher elevations are more deeply developed than those of the soils situated at lower levels. Over 200 soil samples were obtained from 33 main profiles which were analysed granulometrically, chemically and mineralogically. Forty two samples were analysed for pollen-grain content. This work has shown very characteristic results. The granulometric and chemical analyses have shown marked differences among the layers, and mineralogical study has proved the heterogeneity of the profile. The determination of the clay-mineral associations has shown the following regularity: the soils with periglacial layers, developed from sedimentary rocks, have very small or no differences in the whole profile between different horizons or layers. In the case of periglacial layers developed from magmatic or metamorphic rocks, there are more marked differences only between the layers. Differences in the layers are usually in the representation of mixed-layer and interstratified minerals. The result of the pollen-grain analysis, mainly from mud flows, showed a greater frequency of pollen-grain occurrence in which tree pollens dominate. The samples of the basic debris of stamens are poor in sporomorphs and in the number of the pollen trees (pine and birch). There are many possible ways of interpreting the alignment of the periglacial layers. This work has emphasised the necessity for the revision of some soil genetical aspects and of the soil ecological (site conditions) significance of the study of periglacial formations.

Epitaxial P‐Type Germanium and Silicon Films by the Hydrogen Reduction of GeBr4, SiBr4, and BBr3

Epitaxial p‐type films of germanium or silicon with controlled thicknesses and resistivities have been grown on parent substrates using the hydrogen reduction of or , respectively, doped with . The thermochemistry and kinetics related to the growth of these films are discussed, and some comparisons with film growth from or are presented.

Single Crystal Silicon Overgrowths

The pyrolytic process for the vapor phase deposition of single crystal silicon overgrowths on parent substrates is described. This method utilizes the dissociation of silicon tetrachloride by hydrogen in an open tube flow process. Free energy and vapor pressure data are plotted for , , and showing the dissociation relationship between these reacting species for junction formation. Photographs indicate the dependence on temperature of the silicon morphologies that deposit on the substrates, other variables being held constant. Because of the low thermal conductivity of silicon, emphasis is placed on direct contact heating of the silicon substrates to control overgrowth quality. Large temperature gradients were found to exist on the substrate surface with indirect heating by the reactant gases.