THEORY AND MEASUREMENT OF VISUAL MECHANISMS : VIII. THE FORM OF THE FLICKER CONTOUR

Flicker response curves (man) obtained with images formed entirely within the fovea are like those secured with lower animals having only one general class of retinal receptors. They are normal probability integrals (F vs. log I_m), and the properties of their parameters agree with those for visually simplex animals and for the "cone" portions of contours exhibiting visual duplexity. By several different procedures, involving experimental modifications of the "cone" curve, the "rod" part of the typical human duplex curve can be obtained free from overlapping by the extrapolated "cone" curve. It then has the probability integral form which the lower segment does not directly exhibit when combined with "cone" effects. These results are discussed with reference to the statistical nature of the fundamental form of the flicker contour and to the interpretation of duplex curves produced by the neural integration of two independently modifiable groups of sensory effects.     

Maturation of vacuolar (lysosomal) enzymes in yeast: proteinase yscA and proteinase yscB are catalysts of the processing and activation event of carboxypeptidase yscY.

Studies were performed to unravel the activation and maturation mechanism of vacuolar (lysosomal) proteinases in Saccharomyces cerevisiae. In vivo and in vitro studies show that proteinase yscA and proteinase yscB are involved in the activation and processing event of pro-carboxypeptidase yscY. Processing and activation of pro-carboxypeptidase yscY by proteinase yscA depends on an additional factor contained in the vacuolar fraction. Comparable activation can be mimicked by sodium polyphosphate. Optimum pH for processing by this proteinase yscA-triggered event is 5. The proteinase yscA-triggered maturation process of pro-carboxypeptidase yscY leads to an intermediate mol. wt form of the enzyme which is, however, fully active. Proteinase yscB transfers the intermediate mol. wt form of the original precursor to the apparently authentic, mature and active carboxypeptidase yscY. An activation and maturation scheme is devised.     

NMR in vitro measurements: a quality control study of the RADX table-top spectrometer

A series of experiments was performed to evaluate the accuracy and reproducibility of relaxation values obtained by two RADX table-top spectrometers operating at 5 MHz (R5) and 10 MHz (R10) respectively. The output (T1, T2, and proton content) of each machine was compared (for tissue specimens and paramagnetic solutions) to reference spectrometers. In the range of tissue T1's, R5 overestimates T1 by approx. 10% and R10 underestimates by approx. 23%. For tissue specimens, the T2 output of both machines is within 3% of the reference facility. Proton content values correlate well with the % wet weight of tissues (y = .46x + 24, r = .85) but accuracy deteriorates badly if tissue T1 greater than 400 msec or T2 greater than 300 msec. The output of both machines is accurate and reproducible within 5% over the range of tissue relaxation values (biological fluids excluded).     

Auswirkungen der Methode der Linearisierung des μ-cs-Verlaufs auf die Parameteranpassung bei dem Monodschen Modell

Nowadays, the MONOD conception is the foundation for modelling the growth-connected substrat consumption. The methods of the parameter estimation for μ_max and K_s have a variable exactness. Using the experimental MONOD 's data [1] variable graphical and numerical methods are analyzed from the point of statistical view. Appropriate objective functions are proposed.     

Flavonoid diversity and endemism in Arnica subgenus Austromontana

Eighty-seven populations, representing eight species of Amica subgenus Austromontana, were examined for flavonoids. A total of 22 compounds, including simple and methylated flavone and flavonol glycosides as well as methylated aglycones, were isolated and identified. The two widespread species, A. cordifolia and its presumed early derivative A. latifolia, are ancestral species of the subgenus. From these two species, major evolutionary diversification within the subgenus has taken place largely in the Klamath region of Oregon and California, resulting in the formation of several rare, endemic species. These endemics are generally characterized by reduced flavonoid profiles and/or an increase in the number of methylated aglycones while, in contrast, the wider ranging species have few methylated aglycones and more glycosides. However, one species, A. viscosa, a rare volcanic endemic, exhibits the most elaborate and specialized flavonoid profile within the subgenus.     

Effects of forest edge on populations of white-footed mice Peromyscus leucopus

Several studies have reported higher densities of white-footed mice in small fragments than in large fragments of eastern deciduous forests. The edge hypothesis states that higher densities in smaller fragments reflect an increase in relative amount of edge habitat, which supports higher densities of mice because of its higher quality. To test this hypothesis we live trapped white-footed mice along edge-to-interior gradients in forest fragments of east-central Illinois. Our results indicated a greater abundance of mice in the forest interior than near the edge, which did not support the edge hypothesis. This pattern could occur because dominant adults hold larger territories of higher quality habitat, thereby reducing density and increasing fitness near the edge (an ideal despotic distribution). We found some evidence of increased reproductive success (juveniles per female) at the edge, but this could reflect density-dependent demographic processes rather than habitat quality. Furthermore, other indicators of dominance (body weight, and reproductive activity) did not show an increase at the edge, and other studies indicate higher prevalence of natural enemies at edges, which could account for lower densities there. Reduced competition from larger rodents and reduced predation could cause higher densities in small fragments but the distributions of competitors and predators do not strongly support these hypotheses. We suggest two additional hypotheses that could account for greater densities in smaller fragments: 1) estimates of high densities could be artifacts of the large effect that a few captures can have on density estimates for very small fragments, and 2) densities in smaller fragments are overestimated because mice use a relatively larger area of surrounding habitat as fragment size decreases.     

Phylogenetic position of the Sphaeropleaceae (Chlorophyta)

 The complete 18S rRNA gene sequences of four Sphaeroplea C.A. Agardh strains (Sphaeropleales, Sphaeropleaceae), two Atractomorpha Hoffman strains (Sphaeropleales, Sphaeropleaceae) and two Ankyra Fott strains (Chlorococcales, Characiaceae) were determined and subjected to phylogenetic analyses. The analyses indicated that all these taxa belong to a monophyletic lineage (Sphaeropleaceae) and are related to a group of chlorophycean algae comprising autosporic taxa and taxa that reproduce by zoospores which are characterized by directly opposed basal bodies. The taxonomic assignment of the Sphaeropleaceae as a family within the Sphaeropleales (Chlorophyta, Chlorophyceae) is discussed. Received December 22, 2000 Accepted September 25, 2001     

The hydrodynamic characterization of waxy maize amylopectin in 90% dimethyl sulfoxide–water by analytical ultracentrifugation, dynamic, and static light scattering

Static light scattering of high amylopectin waxy maize starch gently dispersed in 90% dimethyl sulfoxide–water yielded a weight average molecular weight M_w and radius of gyration R_g of 560×10⁶ g/mol and 342 nm, respectively. To obtain an independent hydrodynamic characterization of these solutions, we measured the sedimentation coefficient for the main component in an analytical ultracentrifuge. The value of s⁰, the infinite dilution sedimentation coefficient, was 199 S. The translational diffusion coefficient D⁰ in very dilute solutions was measured by dynamic light scattering at 90° and found to be 2.33×10⁻⁹ cm²/s. An effective hydrodynamic radius R_h was calculated from this diffusion constant using the Stokes–Einstein equation and found to be 348 nm. The structure-related parameter ρ=R_g/R_h was calculated to be 0.98. The weight average molecular weight calculated from the Svedberg equation using the values measured for s⁰ and D⁰ was 593×10⁶ g/mol. This result is in reasonable agreement with the light scattering results. As light scattering results are subject to experimental errors due to the possibility of dust contamination, the presence of microgel or aggregates, and the questionable applicability of light scattering theory to interpret results for macromolecular sizes approaching the wave length of light used as a source for scattering, it is advisable to have corroborating hydrodynamic data when possible to further validate light scattering results in this very high molecular weight range.