Effect of ethanol on the specific transport system for L-lysine inSaccharomyces cerevisiae

Preincubation of resting cells of Saccharomyces cerevisiae double mutant can1 gap1 (with a single transport system for L-lysine) with metabolic substrates stimulated subsequent uptake of lysine. While in the wild type the stimulation is connected primarily with carrier protein synthesis (delayed, cycloheximide-inhibitable effect) in the mutant an immediate tapping of an energy source (antimycin-inhibited) is practically solely involved.     

Luminance artifacts of cathode-ray tube displays for vision research.

Phosphor persistence, video bandwidth, DC restoration and high-voltage regulation affect the appearance of images presented on cathode-ray tubes (CRTs), potentially resulting in differences between nominal and actual stimuli. We illustrate these effects by measuring physical parameters of horizontal and vertical static and counter-phase flickering gratings, and we illustrate problems for vision research by measuring contrast sensitivity to these gratings. We also measured the extent to which calibration protocols actually result in the monitor being calibrated over its entire area regardless of image size. The results of our physical measurements indicate substantial differences between gratings that nominally differ only as to orientation. Consistent with these differences, our psychophysical measurements indicate different sensitivities when the bars of the gratings are parallel or orthogonal to raster lines, regardless of the retinal orientation of the gratings. The results of our calibration check show that only a small region around the target area of calibration can be regarded as effectively linearized, and only if the size of the test image used during the check is similar to the size of the calibration patch. Overall, our results indicate potentially severe problems with the use of CRTs in vision research, and we discuss some published results that are likely to have been affected by these problems.     

Studies on the simultaneous production of single cell protein and polygalacturonase fromKluyveromyces fragilis

Summary Kluyveromyces fragilis produces polygalacturonase (PG) on a lactose medium. Although the enzyme is normally repressed at high aeration levels, significant amounts of PG can be produced under such conditions when pectin is added as inducer. The productivity and yield of cell mass were not significantly affected by the presence of inducer, suggesting potential applications to current single cell protein processes from whey.     

Phytochrome Regulation of the Response to Exogenous Gibberellins by Epicotyls of Vigna sinensis

The elongation rate of cowpea epicotyls from whole cowpea (Vigna sinensis) seedlings and derooted and debladed plants (explants) increased after the main light period (8-hour duration) was extended with either continuous low intensity tungsten light or brief (5 minutes) far-red (FR) irradiation. This end-of-day FR effect was reversed by red (R) irradiation suggesting the involvement of phytochrome. These results confirm and extend those obtained previously with other species. Localization studies indicate the epicotyl to be the site of the photoreceptor. Treatment of cowpea seedlings with paclobutrazol, a gibberellin (GA) biosynthetic inhibitor, abolished the FR promoted epicotyl elongation, indicating a role for GAs in this process. There was no significant difference in epicotyl elongation rates of R plus FR irradiated explants treated with GA₁ or GA₂₀ and R irradiated explants treated with GA₁. However, R irradiation inhibited subsequent epicotyl elongation of GA₂₀ treated explants. Moreover, the observation, using GC-MS, that GA₁ and GA₂₀ are native GAs in cowpea lends support to the concept that phytochrome may control the conversion of endogenous GA₂₀ to GA₁ in cowpea.     

Chromaffin cell calcium channel kinetics measured isotopically through fast calcium, strontium, and barium fluxes

Fast Ca2+ uptake into K+-depolarized cultured bovine adrenal chromaffin cells has been isotopically measured in a time scale of 1-10 s. Depolarized cells retained as much as 80-fold 45Ca2+ taken up by resting cells; Ca2+ was not taken up by fibroblasts or endothelial-like cells. Because Ca2+ entry was inhibited by inorganic (La3+, Co2+, Mg2+) and organic (nifedipine) Ca2+ channel antagonists and enhanced by the Ca2+ channel activator Bay-K-8644, it seems clear that Ca2+ gains access to the chromaffin cell cytosol mainly through specific voltage-dependent Ca2+ channels. Ca2+ uptake evoked by 59 mM K+ was linear during the first 5 s of stimulation and continued to rise at a much slower rate up to 60 s. The rate of Ca2+ entry became steeper as the external [Ca2+] increased; initial rates of Ca2+ uptake varied from 0.06 fmol/cells . s at 0.125 mM Ca2+ to 2.85 fmol/cell . s at 7.5 mM Ca2+. The early 90Sr2+ uptake was linear but faster than Ca2+ uptake and later on was also saturated; 133Ba2+ was taken up still at a much faster rate and was linear for the entire depolarization period (2-60 s). Increased [K+] gradually depolarized chromaffin cells; Ca2+ and Sr2+ uptakes were not apparent below 30 mM K+ but were linear for 30 to 60 mM K+. In contrast, substantial Ba2+ uptake was seen even in K+-free solutions; and in 5.9 mM K+, Ba2+ uptake was as high as Ca2+ uptake obtained in 60 mM K+. Five to ten-second pulses of 45Ca2+, 90Sr2+, or 133Ba2+ given at different times after pre-depolarization of chromaffin cells served to analyze the kinetics of inactivation of the rates of entry of each divalent cation. Inactivation of Ca2+ uptake was faster than Sr2+, and Ba2+ uptake inactivated very little. Neither voltage changes nor Ca2+ ions passing through the channels seems to cause their inactivation; however, experiments aimed to manipulate the levels of internal Ca2+ using the cell-permeable chelator Quin-2 or the ionophore A23187 strongly suggest that intracellular Ca2+ levels determine the rates of inactivation of these channels.     

Studies on evolutionary and selective properties of hypercycles using a Monte Carlo method

Summary The most relevant properties of hypercycles were previously studied mainly from a theoretical point of view. We have developed a Monte Carlo method simulating hypercyclic organization to obtain information about the dynamics of this prebiotic organization. Nucleation, growth, and selective properties have been tested and the results obtained are in good agreement with those of the theoretical predictions. The influence of hypercyclic organization of the error threshold has also been studied. As a consequence of the emergence of a hypercycle, the value of this threshold decreases. The amount of this decrease depends on the population size. Moreover, for some interval of quality factor values, either the hypercycle organization or an error catastrophe can be produced, depending on the initial conditions. The influence of these phenomena on both the dynamic behavior and evolutionary advantages of the hypercycle, as well as their decisive roles on genome size, are discussed.Presented at the FEBS Symposium on Genome Organization and Evolution, held in Crete, Greece, September 1–5, 1986     

A kinetic study of the melanization pathway between L-tyrosine and dopachrome

In the pathway of melanin biosynthesis originating from L-tyrosine, the dopachrome accumulation at physiological pH is produced with a pronounced lag period, during which the level of L-dopa increases, following a sigmoidal kinetics to reach a steady-state. A kinetic model has been proposed for the overall pathway of melanization from L-tyrosine to dopachrome; it explains the lag period present during the dopachrome accumulation as well as the influence of L-tyrosine and tyrosinase over this lag period. Use of this model is also valid to explain the kinetics of L-dopa accumulation in the reaction medium, as has been tested by simulation.     

Biochemical indicators of water stress in sunflower seedlings

The free proline and chlorophyll contents, and the chlorophyllase, peroxidase and nitrate-reductase activities were determined in sunflower seedlings grown under controlled conditions and submitted to water stress induced by 14 % polyethyleneglycolj (M_r = 4000) or isotonic NaCl solution. Combined free proline content and peroxidase activity may be used for detection of the factor inducing water stress.