Zeitschrift fur Naturforschung. Section C, Biosciences最新文献

The kinetic of the reversible dissociation of glycerol dehydrogenase from Bacillus megaterium in slightly alkaline medium was measured by biochemical, chemical and physical methods. The dissociation is followed by changes in the secondary structure and can be prevented by addition of NAD or increased potassium chloride concentration. Crosslinking by suberimidate, but not by monofunctional imido esters, shows a high stabilization against alkali, urea or heat inactivation caused by hindrance of dissociation.

Osmotic shock was applied to phage T2 in such a manner that the compact-mass of DNA was released from phage. The shape of this compact-mass of DNA was studied under electron microscope. It appeared that the DNA was packed into an elongated icosahedron similar to the phage head.

Accumulated experimental information is used to assess the possible significance of thermal diffusion to mass transport in living matter. Possible thermal gradients across membranes, a single living cell, and an ensemble of such cells (e.g. an organ, tumor, etc.) are estimated. The corresponding model calculations, although not describing the biological process in detail, lead to conclusions about the possibilities for thermal diffusion as follows. Adequate thermal gradients to support substantial thermal diffusion could exist across biological membranes. Thermal diffusive flow would become significant when ordinary Fickian diffusion is sufficiently suppressed, e.g. in more concentrated systems near critical points of solution (i.e. near incipient phase separations). Conditions favorable to thermal diffusion functioning as a mechanism for active transport appear possible. Thermal diffusion appears much more important for transport into and out of an ensemble of cells than into or out of a single cell. Such mass transport by thermal diffusion could assume a sizable magnitude for an ensemble of cells with the dimensions of an organ or a tumor.

The calcium-dependent acylphosphate formed by the calcium transport ATPase of cardiac sarcoplasmic reticulum and the calcium-, calmodulin-dependent phosphoester(s) of sarcoplasmic reticulum fractions formed by a calcium-, calmodulin-dependent membrane-bound protein kinase can be distinguished by removal of calcium and/or magnesium by EDTA or hydroxylamine treatment of the acid denaturated membranes. Both procedures decompose the acylphosphate with little effect on the phosphoester(s). Calmodulin-dependent phosphorylation (2.44 nmol/mg SR protein) reduces the apparent K(Ca) of the acylphosphate steady state level of the calcium transport ATPase from 0.56 to 0.34 microM free calcium, without affecting the maximum phosphoenzyme level (0.93 versus 0.89 nmol/mg protein), and has little, if any, effect on the Hill-coefficient (1.32 versus 1.54).

Two classes of tributyltin (TBT) resistant, spontaneous mutants of Escherichia coli K-12 were isolated, using a cytochrome containing (W 1485) and a cytochrome deficient ( SASX76 ) strain. In contrast to the cytochrome sufficient strain, the cytochrome deficient strain was found to be fifty times more sensitive to TBT. The class I mutants, isolated from strain W 1485, also showed cross-resistance to triphenyltin (TPT). As compared to its wild type parent, the TBT-resistant mutants exhibited mucoid colony type, aberrant cell morphology and reduced uptake of TPT. Based on these results, it was suggested that the resistance of class I mutants to TBT may be associated with above mentioned alterations. The class II TBT-resistant mutants were isolated from the cytochrome deficient strain, SASX76 . In comparison to class I mutants, these class II mutants were found to have TBT-resistant membrane bound adenosine triphosphatase (ATPase) which may account for their resistance to TBT.

Ribonucleoside diphosphate reductases isolated from Escherichia coli, baker's yeast, Ehrlich ascites tumor cells, and unicellular green alga (Scenedesmus obliquus) are inhibited strongly and uniformly by the polymeric triphenylmethane dye, aurintricarboxylic acid. The molecule appears to interact simultaneously with the enzyme's various nucleotide and catalytic (iron-organic radical) sites. Oligo- and polyribonucleotides are also inhibitory. These reactions serve as models of the probably physiologic regulation of ribonucleotide reduction exerted by natural inhibitors. Partial characterization of an inhibitor fraction found in wheat seed embryo is described.

Photodestruction of Propionibacterium acnes was investigated by broad-band near-ultraviolet light. The inactivation of the bacteria was found to be oxygen dependent, and without O2 practically no photoinactivation occurred. D2O caused an increased inactivation (D10 = 5 kJ/m2 in D2O as compared to D10 = 11 kJ/m2 in normal water). Decreased temperature during illumination increased the ability to form colonies. The results are compared with corresponding results for other types of cells and the destruction mechanism is discussed.

The effect of pressure on the calcium dependent hydrolysis of para-nitrophenyl phosphate by the calcium transport enzyme of the sarcoplasmic reticulum was studied under different conditions: temperature, solutes, substrate and ion concentrations. The calcium transport enzyme exhibits a large positive activation volume which does neither depend on the enzyme's inhibition by high salt concentrations nor its activation by ethylene glycol. The activation volume further proves to be pressure-independent but exhibits a pronounced negative temperature coefficient. The volume changes connected with the entrance of para-nitrophenyl phosphate, calcium or magnesium ions into the substrate ion complex are quite small, indicating that the transfer of water connected with the binding of these ligands is compensated by volume changes of the protein, accompanying the transition of the enzyme from its activated into its ground state.

A reaction mechanism is presented for strand break formation in poly U induced by OH radicals in N2O/O2- saturated aqueous solution based on experimental results obtained with different methods.

Tetrahymena cells treated with purified rabbit antibodies to rat hepatocellular membrane exhibited a considerable increase in binding capacity on reexposure to the antibody 24 h later. Insulin binding was similarly enhanced by preexposure to the antibody, and vice versa, preexposure to insulin enhanced the later binding of rat liver receptor antibodies. This suggests that (1) the Tetrahymena and the rat possess similar insulin receptors, and (2) the receptor antibody is also able to induce imprinting for itself as well as for insulin. Concanavalin-A, noted for binding overlap with insulin, failed to induce imprinting either for insulin or for antibodies to receptors, whereas the latter did induce imprinting for Concanavalin-A.