The enzymatic system thiosulfate: Cytochrome c oxidoreductase from photolithoautotrophically grown Rhodopseudomonas palustris

Rhodopseudomonas palustris cells, characterized by a lamellar type intracytoplasmic chromatophore membrane system after phototrophic growth, yielded a crude supernatant cell-free fraction (S-144) after ultracentrifugation which retained the contents of both the cell compartments. After thiosulfate-dependent growth, a protein system was isolated from S-144 which catalyzed the thiosulfate-linked reduction of an endogenous c-type cytochrome. — The colorless oxidoreductase protein, after purification to homogeneity, revealed a molecular weight of 93,000 and, after SDS treatment, a particle weight of 48,000. It was focused at an average pI of 5.45. Apparent K _m values for several substrates were in the M range. The electron acceptor for thiosulfate oxidation was found to be a cytochrome c from S-144. The homogeneous acceptor protein, at liquid nitrogen temperature, exhibited absorption maxima at 549.0, 518.5 and 418.0 nm, and shoulders at 525.5, 512.0 and 508.0 nm. Its molecular weight was found to be 17,000 (gel filtration) and 16,000 (SDS gel electrophoresis). It was characterized by a pI of 10.0. Its midpoint redox potential of E _m,7.0=+228 mV was determined by redox titrations and the value of +205 mV by spectrophotometric calculations.Abbreviations BSA bovine serum albumin - HiPIP high potential nonheme iron protein - IEF isoclectric focusing - SDS dodecylsulfate, sodium salt - Temed N,N,N,N-tetramethylethylenediamine     

Effect of Mg2+ and spermine on the kinetics of Ca2+ transport in rat-liver mitochondria

Plots relating the initial rate of mitochondrial Ca²⁺ transport to the Ca²⁺ concentration (kinetic plots) have a hyperbolic shape in a Ca²⁺ concentration range of 2.5–100 µM as measured in sucrose or KCl media. In the presence of Mg²⁺ or a polyamine spermine, which both are competitive inhibitors of Ca²⁺ binding to low affinity sites at the membrane surface, the shape of the plots becomes sigmoidal. At higher concentrations of these agents linear kinetic plots are obtained as measured in a sucrose medium. In a KCl medium the sigmoidality of the kinetic plots is enhanced by an increase in the Mg²⁺ or spermine concentration. It is suggested that Mg²⁺ and spermine affect the kinetics of Ca²⁺ transport by interfering with Ca²⁺ binding to low affinity sites of the membrane surface and that the binding of Ca²⁺ to these sites is the first step of the mitochondrial Ca²⁺ transport.     

The phenoloxidases of the ascomycete Podospora anserina. XIII. Action and interaction of genes controlling the formation of laccase.

1. Eight mutants were isolated following mutagen treatment which are deficient in laccase formation. Seven of these had a pleiotropic effect and exhibited defects in growth rate and in mycelial and sexual morphology. 2. By means of tetrad analysis the mutations were assigned to 6 loci. Three mutations were in the incolora locus, the others were non-allelic. Only two of these loci were closely linked. 3. All genes exhibit numerous interactions. These concern the morphological expression of the laccase genes and also the laccase spectra. 4. The mutants could be separated into four classes on the basis of the amount and type of laccase produced. 5. Five of the loci studied appear to be structural genes because mutations alters the physical properties of the laccase protein. The sixth gene has a regulatory role.     

Two new C-methylated flavonoids from Myrica gale

From the leaves of Myrica gale 2′,4′-dihydroxy-6′-methoxy-3′,5′-dimethylchalcone has been isolated. The fruits yielded 2′-hydroxy-4′,6′-dimethoxy-3′-methyldihydrochalcone. The constitutions were deduced from spectroscopic data and confirmed by synthesis.     

Mass spectrometry of silylated flavonol O-glycosides

The electron impact mass spectra of 19 trimethyl silylated flavonol mono-, di- and -triglycosides are reported for the first time. All spectra show wel     

Initial phases of indoleacetic acid induced growth in coleoptile segments of Avena sativa L.

The intial phases of auxin-induced growth in coleoptile segments of Avena sativa L. were investigated using a high resolution growth recording technique, based on an angular position sensing transducer. The first response to the hormone is a slight, transient reduction of the growth rate lasting about 5 min. After this phase growth rate increases to a maximum. The duration of the increase and the maximum clearly depend on the concentration of the hormone. With increasing auxin concentration the duration of the growth rate increase is reduced from about 80 min in 10^-9 M indoleacetic acid (IAA) to about 14 min in 10^-4 M IAA. After the maximum the growth rate declines. Looking at the maximum of the growth rate, we obtained a dose-response curve with a sharp increase between 10^-9 M and 10^-6 M IAA and a slight decline between 10^-6 M and 10^-4 M IAA. This result is confirmed by growth rates measured one and two hours after the application of the hormone.Abbreviations IAA indoleacetic acid     

Ion transport across the isolated intestinal mucosa of the winter flounder,Pseudopleuronectes americanus

The isolated intestinal mucosa of the flounder, Pseudopleuronectes americanus, when bathed in a 20 mM HCO3-Ringer's solution bubbled with 1% CO2 in O2, generated a serosa-negative PD and, when short-circuited, absorbed Cl at almost 3 times the rate of Na. Reducing HCO3 to 5 mM decreased the net Cl flux by more than 60%. The following results suggest that, despite the PD, Na and Cl transport processes are nonelectrically coupled: replacing all Na with choline abolished both the PD and net Cl flux; replacing all Cl with SO4 and mannitol abolished the PD and the net Na flux; and adding ouabain (to 0.5 mM) abolished the PD and the net Cl flux. Nearly all of the unidirectional serosa-to-mucosa Cl flux (JClsm) seemed to be paracellular since it varied with PD and Cl concentration in a manner consistent with simple diffusion. JClsm was only about one-fourth of JNasm, suggesting that the paracellular pathway is highly cation-selective. The data can be explained by the following model: (i) Na and Cl uptake across the brush border are coupled 1 : 1; Na is pumped into the lateral space and Cl follows passively, elevating the salt concentration there; (ii) the tight junction is permeable to Na but relatively impermeable to Cl; and (iii) resistance to Na diffusion is greater in the lateral space (considered in its entirety) than in the tight junction. If these assumptions are correct, the serosa-negative transmural PD is due mainly to a salt diffusion potential across the tight junction and, under short-circuit condition, most of the Na pumped into the lateral space diffuses back into the luminal solution, whereas most of the Cl enters the serosal solution. Morphological features of the epithelium support this interpretation: the cells are unusually long (60 micrometer); there is little distension of the apical 12 micrometer of the lateral space during active fluid absorption; and distension distal to this region is intermittently constricted by desmosomes.     

Sequence regularities and packing of collagen molecules

Fourier analysis of sequences along edges of the type I collagen molecule constructed from two α1(I) and one α2 chains shows that the molecule is two-sided if the supercoil pitch of the α chains along the molecular axis, P, is 39 residues ($\text{D}\text{6}$, where D = 234 residues or 67 nm). One side has alternating charged and hydrophobic regions with spacings of $\text{D}\text{6}$, while the other side has an excess of hydrophobic residues with a spacing of $\text{D}\text{11}$. These characteristics arise from sequence regularities in the α chains and the geometric relationship between the chains. The pattern is marginally strongest with α2 as chain 1. The $\text{D}\text{6}$ sides could form the inside of a helical microfibril where contacts between molecules would fall P apart along the α chains. The $\text{D}\text{11}$ sides could form the outside of the microfibril where contacts between microfibrils would be spaced apart by the α chain supercoil along the microfibril axis, P′. If the microfibril is a 5₄ helix of D-staggered collagen molecules with a left-handed supercoil of pitch $\text{20D}\text{11}$, P′ is close to $\text{2D}\text{11}$ (43 residues). $\text{2D}\text{11}$ subsets in the α chains give rise to the $\text{D}\text{11}$ spacing along the molecule. The microfibril has 4₁ screw symmetry satisfying X-ray diffraction evidence that microfibrils pack in a tetragonal unit cell.This model is the same as proposed previously by us (Trus & Piez, 1976: Piez & Trus, 1977) except that P = 39 rather than 30 residues. Contrary to our earlier assumption, P = 39 residues is within the range allowed by X-ray diffraction measurements. The present results favor P = 39 since it relates regularities in the α chain sequences to helical parameters in a direct way. Furthermore, model studies show that geometric arguments which support P = 30 are equally strong at P = 39 residues.     

Evidence for plasmid like DNA in a filamentous fungus, the ascomycete Podospora anserina

Summary The existece of plasmid like DNA was demonstrated in senescent mycelia of Podospora anserina (strain s) by biophysical and electronmicroscopic methods. According to their contour length of about 1.4 and 2.7 m respectively the molecular weight for the monomer is in the range of 3·10⁶.This work was supported by the Deutsche Forschungsgemeinschaft. The sojourn of P.A.L. for six months in Bochum was made possible by a Senior U.S. Scientist Award of the Alexander von Humboldt Stiftung (Bonn).     

Effects of cAMP,theophylline, imidazole,and 4-(3,4-dimethoxybenzyl)-2-imidazolidone on the leaf movement rhythm of Trifolium repens—a test of the cAMP-hypothesis of circadian rhythms

The period length of the leaf movement rhythm of Trifolium repens L. is lengthened by continuously offered cAMP (0.5–1.0 mol m^-3) and theophylline (0.5–4 mol m^-3). At the higher concentrations this effect is more pronounced and the rhythm damps out faster. Imidazole (0.5 and 1 mol m^-3) has no effect on the period length; however, after 5 mol m^-3 the rhythm is abolished. Offered as 4 h pulses the resulting phase response curves for cAMP and imidazole are similar and show delays of up to 4 h during the day position of the leaves. Theophylline pulses lead to delays of up to 5 h during closure and advances of up to 3 h during opening. No phase shift is brought about by 4-(3,4-dimethoxybenzyl)-2-imidazolidone. The results do not support the cAMP-model of the circadian clock which has been proposed by Cummings (J. theor. Biol. 55, 455–470; 1975). The effect of the substances tested could, however, be based upon influences on the transport of Ca²⁺.Abbreviations ATP adenosine triphosphate - cAMP cyclic adenosine 35 monophosphate - AMP adenosine 5 monophosphate - AC adenyl cyclase - PDE phosphodiesterase - LL continuous light