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191.
Liposomes were prepared from phosphatidylcholine and cardiolipin in a KCl medium and suspended in a choline chloride medium with safranine. When efflux of K+ was induced by valinomycin, spectral shifts characteristic of stacking were observed. Ca2+ inhibited the rate of stacking in a competitive manner with a Ki of about 200 μM, while La3+ was about 10 times more potent. When liposomes were prepared from phospholipids with a higher ratio of cardiolipin to phosphatidyl-choline the inhibition was more potent. No effect on the stacking phenomena was seen when Ca2+ was added after the stacking was completed. When Ca2+ or an organic cation with four charges, spermine, was trapped in the intraliposomal compartment, no significant change in the rate of stacking was seen. However, the extent of stacking was decreased. It is suggested that safranine is driven by a diffusion potential to a site that is inaccessible to Ca2+ in the medium, presumably to the inner boundaries of the liposomal membranes. 相似文献
192.
Günther Boheim Karl Janko Dieter Leibfritz Tadaaki Ooka Wilfried A. König Günther Jung 《生物化学与生物物理学报:生物膜》1976,433(1):182-199
Suzukacillin, a polypeptide consisting of presumably 23 amino acids and 1 phenylalaninol, is produced by a Trichoderma viride strain No. 1037 and it can be isolated from the culture medium. It shows membrane-modifying properties similar to those of alamethicin. Discrete conductance fluctuations indicate the formation of oligomer pores of varying diameter. On the basis of voltage jump relaxation experiments evidence is given that the dimer is the nucleation state from which pore formation tion starts and the oligomer disappears. According to the voltage-current characteristics, voltage-dependent and voltage-independent conductances are observed. A slow process is involved, which can be interpreted as a change in the equilibrium distribution between different conformations of the suzukacillin monomer at the membrane interphase. This change results from its interaction with the lipid matrix. Differences in experimental observations between suzukacillin and alamethicin are attributed to the relatively larger α-helix and higher number of aliphatic side chains of the suzukacillin monomer and to a more intense interaction with the lipid membrane. This leads to a higher probability of forming dimers from monomers and to the occurrence of “inactivation”. 相似文献
193.
1. An already published test method for detecting bactericidal substances in paper chromatograms was further improved. 2. In cultures of Cosmarium impressulum free from bacteria, two bactericidal substances were found in the ether extracts from the algae and two others in the extracts of the culture medium. The are active against some or all bacteria testes (Serratia marcescens, Pseudomonas fluorescens; Aerobacter aerogenes or Bacillus pumilus). 3. If the culture medium of Cosmarium or another desmidiale was inoculated with the test bacteria, a clear bactericidal effect was never observed. 4. Because the activity of the bactericidal substances of Cosmarium is only small and the formation is not constant, it is concluded that the water-soluble bactericidal substances of the alga are not the cause that epiphytic bacteria do not grow normally on Cosmarium. 相似文献
194.
Summary A population of nerve fibres in the gastro-intestinal tract of mice showing a high affinity for quinacrine was revealed by fluorescence microscopy. Similar results were obtained in rats and guinea pigs. Whole-mounts of sheets of the smooth muscle layer following incubation in 10-6-10-7 M quinacrine for 15–60 min revealed fine fluorescent varicose nerve fibers in the myenteric plexus of Auerbach both around nerve cell bodies and in the interconnecting strands. Many fibers were also present between the strands of the plexus, especially running parallel to the circular muscle layer. Such fibers were not seen in similarly quinacrine-incubated irides. A proportion of the cell bodies in Auerbach's plexus also showed quinacrine accumulation. These cells were apparently smaller neurons, sometimes with fluorescent processes. Intraperitoneal injections of quinacrine failed to demonstrate nerve fibers, but some cell bodies in Auerbach's plexus were positive. Subsequent paraformaldehyde treatment for monoamine visualization showed persistent adrenergic nerve terminals in the intestine and iris. These nerves seemed to be fewer and had a more yellow fluorescence than normally. The identity of the quinacrine-positive fibers is discussed with respect to recent suggestions that purinergic, substance P, enkephalin, and somatosin-containing nerves, in addition to adrenergic and cholinergic nerves, are present in the gut wall.Supported by the Swedish Medical Research Council (04X-03185). Magnus Bergvalls Stiftelse and Karolinska Institutets Fonder. For generous gifts of Mepacrine we thank Winthrop, Skärholmen, Stockholm, Sweden. The skilful technical assistance of Miss Gerd Boetius and Miss Maud Eriksson is gratefully acknowledged 相似文献
195.
Mutants of Bacillus subtilis constitutive for L-leucine dehydrogenase synthesis were selected. Using these mutants we could determine two functional roles for the L-leucine dehydrogenase. This enzyme liberates ammonium ions from branched chain amino acids when supplied as the sole nitrogen source. Another function is to synthesize from L-isoleucine, L-leucine, and L-valine the branched chain -keto acids which are precursors of branched chain fatty acid biosynthesis. These results together with the inducibility of the enzyme suggest that the L-leucine dehydrogenase has primarily a catabolic rather than an anabolic function in the metabolism of Bacillus subtilis. 相似文献
196.
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198.
Starting from the histone mixture obtained from calf thymus, the arginine rich fraction ARE+) was coupled to organomercurial agarose via a mercaptide bond to one of its cysteines. ARE-agarose proved to be useful for a large scale affinity chromatographic separation of whole histone. In 1M NaCl, pH 4.5, highly pure histone fractions could be eluted with an urea gradient revealing increasing affinity towards ARE in the order: KAP < KAS < LAK < (ARE)n(GRK)n < GRK < ARE. 相似文献
199.
R C Karl W S Zawalich J A Ferrendelli F M Matschinsky 《The Journal of biological chemistry》1975,250(12):4575-4579
Insulin release from isolated perifused pancreatic islets was stimulated by the divalent ionophore A23187 in the absence of exogenous glucose. In addition, A23187 produced a 2-fold elevation of cyclic adenosine 3':5'-monophosphate (cAMP) levels in isolated perifused islets. The elevation of cAMP levels coincided with peak insulin release. Ionophore-induced insulin release was unaffected by pretreatment of the islets with theophylline (5 mM). Stimulation of insulin release produced by the ionophore occurred either in the presence or absence of extracellular Ca-2+; however, cAMP accumulation required the presence of extracellular Ca-2+. The ionophore (10 muM) had no effect on adenylate cyclase activity of homogenates of isolated islets. The results of this study are interpreted as indicating that intracellular Ca-2+ has an essential role in the insulin releasing mechanism, whereas the cAMP system has a modulatory effect on this process. 相似文献
200.
Alanine and glutamine formation and release were studied using the intact epitrochlaris preparation of rat skeletal muscle. Epinephrine reduced the release of alanine and glutamine in a concentration-dependent manner. Measurable inhibition was observed at 10(-9) M epinephrine, and maximal inhibition was obtained at 10(-5) M. Norepinephrine also reduced alanine and glutamine formation and release but the concentration required for maximal inhibition was approximately 100-fold greater than for epinephrine. Isoproterenol (beta agonist), but not phenylephrine (alpha agonist), reproduced the effects of epinephrine, and propranolol (beta antagonist), but not phentolamine (alpha antagonist), blocked the effect of the catecholamine. N6,O2'-Dibutyryl adenosine 3':5'-monophosphate reproduced the effects of epinephrine and theophylline potentiated the effect of submaximal concentrations of the hormone. Glucagon and prostaglandin E2 had no observable effect on amino acid release. Insulin did not modify the inhibition of alanine and glutamine release produced by epinephrine. Alanine and glutamine formation from added precursor amino acids was unaffected by epinephrine or cyclic adenosine 3':5'-monophosphate. Epinephrine reduced alanine formation in muscles obtained from diabetic rats or animals treated with thyroxine or cortisone. These findings indicate that physiological levels of catecholamines reduce alanine and glutamine formation and release from skeletal muscle. This effect is mediated by a beta-adrenergic receptor and the adenylate cyclase system and can be accounted for by an inhibition of muscle protein degradation. 相似文献