Heterotropic interactions in monomeric βSH chains from human hemoglobin

The O₂ affinity of β^SH chains is lowered by H⁺, inositol hexaphosphate (IHP), and CO₂. As the oxygen affinity of β^SH monomers (β₁^SH) is lower than that of β^SH tetramers (β₄^SH), it is possible that IHP and CO₂ exert their influence on the O₂ affinity of β^SH chains by increasing the dissociation constant of β₄^SH rather than by a direct effect on the molecule. In order to test for this hypothesis we have measured the O₂ affinity of β^SH chains as a function of protein concentration at various concentrations of IHP and inorganic phosphates in the absence and presence of CO₂. From these data association constants for the binding of IHP to β₁^SH and β₄^SH as well as for the equilibrium 4β₁^SH ? β₄^SH were calculated. We found that IHP and CO₂ influence the oxygen affinity of β₁^SH. It was furthermore established that inorganic phosphate enhances the stability of β₄^SH while IHP favors its dissociation in monomers.     

Growth of E. Coli W to high cell concentration by oxygen level linked control of carbon source concentration

The growth of E. coli W in a bench scale fermentor to high cell concentration is described. The method involves growth-linked introduction of ammonia to the culture, sparging the culture with oxygen, and maintenance of aerobic conditions during the final growth phase by gradually and automatically decreasing the concentration of the carbon source, sucrose, in the culture. Thus, the oxygen demand is kept within the limits of the supply capacity, and a linear growth rate during the final phase of growth is obtained. A concentration of 42 g dry cell per liter was obtained. The yield constants for nitrogen and phosphorous were determined and were compared with those obtained using the temperature variation method.     

Migration of Electronic Energy from Chlorophyll b to Chlorophyll a in Solutions

Absorption, emission, and fluorescence excitation spectra of pure solutions of chlorophyll a (Chl a) and chlorophyll b (Chl b) in diethyl ether and of equimolecular mixed solutions of the two pigments, were determined at room temperature as functions of concentration (in the range from 5 × 10^-6 M to 4 × 10^-3 M) and of wavelength of the exciting light (in the regions 380-465 and 550-650 nm). The efficiency of energy transfer from Chl b to Chl a, derived from these data, was found to depend on the wavelength of exciting light. Furthermore, the transfer efficiency calculated from sensitization of Chl a fluorescence by Chl b was substantially smaller than that calculated from quenching of Chl b fluorescence by Chl a. Both these effects are tentatively explained as evidence of superposition of a “fast” energy transfer (taking place before the Boltzmann distribution of vibrational energy had been reached) upon the “delayed” transfer, which takes place after vibrational equilibration. The first-named mechanism is made possible by overlapping of the absorption bands of the two pigments; the second, by overlapping of the emission band of Chl b and the absorption band of Chl a. The first mechanism can lead to repeated transfer of excitation energy between pigment molecules, the second only to a one-time transfer from the donor to the acceptor. Both mechanisms could be of the same, second-order type, with the transfer rate proportional to r^-6. An alternative is for the fast mechanism to be of the first order, with the transfer rate proportional to r^-3, but spectroscopic evidence seems to make this alternative less probable.     

Mannan as a major component of the bud scars of Saccharomyces cerevisiae

Summary Bud scars were prepared from the cell walls of Saccharomyces cerevisiae by means of an exo--d-(13)-glucanase. On acid hydrolysis, these structures were shown to consist of mannose (85%), glucose (4%) and glucosamine (2.7%). In addition the isolated bud scars were incubated either with mercurylabelled Concanavalin A or with Concanavalin A coated colloidal gold. They were then examined by electron microscopy and were found to be heavily marked, indicating the presence of mannan. It was thus shown that mannan is a true component of bud scars, which until now had been thought to consist solely of chitin and glucan.     

Immunochemical studies on mannans of the genusSaccharomyces

Antigenic mannans isolated from the cells ofSaccharomyces fermentati, Saccharomyces rosei,Saccharomyces delbrueckii, Torulopsis colliculosa, Candida albicans andSaccharomyces cerevisiae were examined for their reactivity withSaccharomyces fermentati andCandida albicans antisera. Mannans ofTorulaspora as well asCandida albicans showed high cross-reactivity with the investigated antisera, which could be due to the presence of long side chains established by the partial acetolysis method. The low specific rotations ofSaccharomyces fermentati, Saccharomyces rosei andTorulopsis colliculosa mannans indicate a predominance of β-glycosidio linkages, whereasSaccharomyces delbrueckii andCandida albicans mannans possess predominantly α-linkages.Saccharomyces cerevisiae mannan showed different structural and immunological properties.     

The Structure of Plant Cell Walls: I. The Macromolecular Components of the Walls of Suspension-cultured Sycamore Cells with a Detailed Analysis of the Pectic Polysaccharides

This is the first in a series of papers dealing with the structure of cell walls isolated from suspension-cultured sycamore cells (Acer pseudoplatanus). These studies have been made possible by the availability of purified hydrolytic enzymes and by recent improvements in the techniques of methylation analysis. These techniques have permitted us to identify and quantitate the macromolecular components of sycamore cell walls. These walls are composed of 10% arabinan, 2% 3,6-linked arabinogalactan, 23% cellulose, 9% oligo-arabinosides (attached to hydroxyproline), 8% 4-linked galactan, 10% hydroxyproline-rich protein, 16% rhamnogalacturonan, and 21% xyloglucan.     

Literaturberichte

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