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981.
This paper reports the first Raman spectroscopic study of the potassium complex of the cation-specific antibiotic valinomycin. Complete Raman spectra (140 to 3600 cm?1) of crystalline valinomycin-KSCN and its CCl4, CHCl3 and C2H5OH solutions are presented and used to probe the structure of the complex in these environments. In all cases a single, narrow peak is observed in the ester CO stretch region (1750 to 1775 cm?1) which contrasts strongly with the broad bands observed in solutions of uncomplexed valinomycin. This is consistent with the presence of a single conformation in which all six ester CO groups co-ordinate an enclosed potassium ion. We find that although the ester CO stretch frequencies of the complex are similar in the solid state and in non-polar solution (~1770 cm?1) they are considerably different in the presence of polar solvents (~1756 cm?1); this may indicate that the complexed potassium ion is still free to interact with nearby solvent ions (and possibly its counterion) through gaps in the hydrophobic “shield” provided by the hydrocarbon residues of valinomycin. In contrast the amide CO frequencies of the complex (~1650 cm?1) are solvent-independent. These groups are apparently strongly hydrogen-bonded to provide a rather rigid, compact framework for the complex conformation. 相似文献
982.
Role of ethylene in phytochrome-induced anthocyanin synthesis 总被引:3,自引:1,他引:2
Summary Synthesis of anthocyanin pigments in etiolated cabbage seedlings is influenced by ethylene at concentrations higher than 10 ppb, and etiolated seedlings produce sufficient ethylene to influence their anthocyanin synthesis. When escape of endogenous ethylene from this tissue is enhanced by means of hypobaric treatment, anthocyanin synthesis is accelerated. Stimulation of anthocyanin synthesis by brief red illumination is completely prevented by applied ethylene and indoleacetic acid inhibits anthocyanin synthesis by stimulating ethylene production. Red light reduces endogenous as well as auxin-induced ethylene production and there is a close correlation between light-induced inhibition of ethylene synthesis and stimulation of anthocyanin formation. We suggest that in part photo-induced anthocyanin synthesis is due to a lowered ethylene content in light-treated tissue. 相似文献
983.
984.
1. The variation of the specific stoicheiometric catalatic activity of proto- and deuteroferrihaem with total ferrihaem concentration has been studied at 25 degrees C over a wide range of pH. For deuteroferrihaem the results imply that only monomeric ferrihaem species contribute significantly to the catalatic activity. Protoferrihaem is more highly dimerized in solution and, in this system, contributions to the catalatic activity from both monomeric and dimeric ferrihaem species were observed. The ratio of the specific activity of protoferrihaem monomer to that of dimer varied from approximately 20 at pH7 to 5x10(4) at pH12.2. 2. The specific activity of protoferrihaem monomer closely resembles that of deuteroferrihaem monomer, both in magnitude and pH-dependence. In both cases the activity is inversely proportional to [H(+)]. In contrast, the activity of catalase is independent of pH in the range 5-10. At pH13 the activity of ferrihaem monomer becomes equal to the maximal activity of catalase. The results are in good agreement with those reported by Brown et al. (1970b) and provide support for the assumptions upon which this previous analysis relied. 3. Information from the literature concerning the catalatic activity and dimerization of the iron(III) complex of 4,4',4',4'-tetrasulphophthalocyanine (Waldmeier & Sigel, 1971; Sigel et al., 1971) have been re-analysed. The results imply that both the monomeric and dimeric complexes contribute to catalatic activity and these activities closely resemble those of the corresponding protoferrihaem species. 相似文献
985.
986.
987.
Michael John Charles Rhodes Leonard Stanley Charles Wooltorton 《Phytochemistry》1973,12(10):2381-2387
An enzyme fraction from aged swede root disks catalyses the formation of CoA thioesters of cinnamic acids in the presence of CoA, ATP and Mg2+. The enzyme shows activity only to those cinnamic acid derivatives bearing a phenolic OH group, p-coumaric and ferulic acids being the most active substrates. The requirement for Mg2+ can be replaced by Mn2+, Co2+ or Ni2+. The requirement for ATP could not be replaced by GTP, CTP, UTP, ADP or AMP. ADP and AMP, but not pyrophosphate, inhibited the ATP dependent activation of p-coumarate. The activity was inhibited by N-ethylmaleimide and p-chloro-mercuribenzoate which suggests a requirement for -SH groups for activation. The activity of the enzyme is low in freshly prepared disks but rises during ageing, particularly if the ageing is carried out in the presence of low concentrations of ethylene. 相似文献
988.
The mutations in a series of leucine auxotrophs isolated after treatment with nitrosoguanidine, ultraviolet light, and ICR-191 have been mapped between ilvC and pheA on the Bacillus subtilis chromosome. A fine structure map of the region was constructed by transformation. Analysis of several strains by assaying levels of their leucine bioysnthetic enzymes has shown that the region encodes three enzymes. The order of the genes with respect to the biosynthetic steps catalyzed by the gene products is 1–3–2. 相似文献
989.
An aldolase, which is induced in Pseudomonas testosteroni during growth with p-hydroxybenzoate, preferentially attacks the R form of 4-hydroxy-4-methyl-2-oxoglutarate, a metabolite of protocatechuate catabolism. 相似文献
990.
Membrane Attachment of R-Factor Deoxyribonucleic Acid in Compatible and Incompatible Cell Pairs Following Conjugation 总被引:3,自引:2,他引:1 下载免费PDF全文
Superinfection of an Escherichia coli R(+) strain with a closely related R-factor was associated with the accumulation of replicative intermediates of the superinfecting deoxyribonucleic acid. This deoxyribonucleic acid remains associated with a rapidly sedimenting cell component. 相似文献