In part I a simple gedanken experiment is discussed that clearly develops a connection between the rates of accelerated clocks in special relativity theory and the rates of clocks at different points in a uniform gravitational field in any theory which incorporates the equivalence principle, such as general relativity theory. In part II it is shown that the time dilation effect observed when the rate of a moving clock is compared with that of a clock at rest can be derived by observing the Doppler shift, not only of light waves emitted by the moving clock, but of any periodic wave, e.g., sound.
3-Carboxy-cis,cis-muconate lactonizing enzyme (CMLE; EC 5.5.1.5) from Neurospora crassa catalyzes the reversible gamma-lactonization of 3-carboxy-cis,cis-muconate by a syn-1,2 addition-elimination reaction. The stereochemical and regiochemical course of the reaction is (i) opposite that of CMLE from Pseudomonas putida (EC 5.5.1.2) and (ii) identical to that of cis,cis-muconate lactonizing enzyme (MLE; EC 5.5.1.1) from P. putida. In order to determine the mechanistic and evolutionary relationships between N. crassa CMLE and the procaryotic cycloisomerases, we have purified CMLE from N. crassa to homogeneity and determined its nucleotide sequence from a cDNA clone isolated from a p-hydroxybenzoate-induced N. crassa cDNA library. The deduced amino acid sequence predicts a protein of 41.2 kDa (365 residues) which does not exhibit sequence similarity with any of the bacterial cycloisomerases. The cDNA encoding N. crassa CMLE was expressed in Escherichia coli, and the purified recombinant protein exhibits physical and kinetic properties equivalent to those found for the isolated N. crassa enzyme. We also report that N. crassa CMLE possesses substantially reduced yet significant levels of MLE activity with cis,cis-muconate and, furthermore, does not appear to be dependent on divalent metals for activity. These data suggest that the N. crassa CMLE may represent a novel eucaryotic motif in the cycloisomerase enzyme family.
Abstract– Rhodopsin is the general name for a family of visual pigments that receive light and transmit this signal to the rest of an organism. Chlamydomonas reinhardtii is a unicellular eukaryote whose light‐tracking system consists of a single eye. Through spectral studies of Chlamydomonas ' reaction to light of different wavelengths (action spectroscopy), it has been shown in vivo that the photoreceptor of Chlamydomonas is functionally similar to vertebrate rhodopsin. We seek to characterize the photoreceptor further by identifying the molecule that is incorporated into the rhodopsin of Chlamydomonas forming the chromophore. High performance liquid chromatography analysis of organic extracts of retinaloximes from membrane fractions enriched in eye‐spots and in cells virtually free of interfering carotenoids identified syn‐ all ‐trans as the existing retinaloxime isomer. We conclude that all‐ trans ‐retinal is the native molecule that is available to be incorporated into the rhodopsin of Chlamydomonas and therefore forms the functioning chromophore on binding.
In the yeast Saccharomyces cerevisiae, the family of RHO genes are implicated in the control of morphogenetic events although the molecular targets of these GTP-binding proteins remain largely unknown. The activity of 1,3-β-D-glucan synthase, the product of which is essential for cell wall integrity, is regulated by a GTP-binding protein, which we here present evidence to be Rho1p. Rho1p was found to copurify with Fks1p, a glucan synthase subunit, in preparations of the enzyme purified by product entrapment and was also shown to be depleted by a detergent extraction procedure known to remove the GTP-binding regulatory component. Specific ADP-ribosylation of Rho1p by exoenzyme C3 inactivates glucan synthase activity specified by FKS1 and FKS2 as demonstrated in membrane preparations from fks2 and fks1 deletion strains, respectively, and in the purified enzyme containing Fks1p. Rho1p and Fks1p were co-immunoprecipitated from purified glucan synthase under conditions that maintained enzyme activity in the immunoprecipitate. Putative Rho homologs were also identified and implicated in the regulation of glucan synthase activity from Candida albicans, Aspergillus nidulans, and Cryptococcus neoformans by ribosylation studies. The regulation of 1,3-β-D-glucan synthase activity by RHO1 is consistent with its observed role in morphogenetic control and osmotic integrity. In the yeast Saccharomyces cerevisiae, the family of RHO genes are implicated in the control of morphogenetic events although the molecular targets of these GTP-binding proteins remain largely unknown. The activity of 1,3-β-D-glucan synthase, the product of which is essential for cell wall integrity, is regulated by a GTP-binding protein, which we here present evidence to be Rho1p. Rho1p was found to copurify with Fks1p, a glucan synthase subunit, in preparations of the enzyme purified by product entrapment and was also shown to be depleted by a detergent extraction procedure known to remove the GTP-binding regulatory component. Specific ADP-ribosylation of Rho1p by exoenzyme C3 inactivates glucan synthase activity specified by FKS1 and FKS2 as demonstrated in membrane preparations from fks2 and fks1 deletion strains, respectively, and in the purified enzyme containing Fks1p. Rho1p and Fks1p were co-immunoprecipitated from purified glucan synthase under conditions that maintained enzyme activity in the immunoprecipitate. Putative Rho homologs were also identified and implicated in the regulation of glucan synthase activity from Candida albicans, Aspergillus nidulans, and Cryptococcus neoformans by ribosylation studies. The regulation of 1,3-β-D-glucan synthase activity by RHO1 is consistent with its observed role in morphogenetic control and osmotic integrity.
We extend the method used in an earlier paper by the present authors to calculate here the effect of surface roughness on the van der Waals force between two different, semi-infinite dielectric media, separated by a region of vacuum of nominal thickness $l$, when both surfaces of the two media are rough. The result obtained has the form $f(l)=\ensuremath{-}\frac{{c}_{3}}{{(\frac{l}{a})}^{3}}\ensuremath{-}(\frac{{\ensuremath{\delta}}^{2}}{{a}^{2}})[\frac{{c}_{4}}{{(\frac{l}{a})}^{4}}+\frac{{c}_{5}}{{(\frac{l}{a})}^{5}}+\ensuremath{\cdots}]+O(\frac{{\ensuremath{\delta}}^{4}}{{a}^{4}})$ in the limit $\frac{l}{a}$ is large. Here $a$ is the transverse correlation length, the mean distance between consecutive peaks and valleys on the rough surface, while $\ensuremath{\delta}$ is the root-mean-square departure of the surface from flatness. For simplicity, $a$ and $\ensuremath{\delta}$ are assumed to be the same for both surfaces. The terms in the series multiplying the factor ($\frac{{\ensuremath{\delta}}^{2}}{{a}^{2}}$) have been calculated through terms of $O({(\frac{l}{a})}^{\ensuremath{-}7})$ for three different assumptions about the correlation between the roughness profile functions on the two surfaces. In addition, in the Appendix we show that a simple effective medium model of surface roughness, that has previously been shown to reproduce accurately the effects of surface roughness on the image potential and on the surface-plasmon dispersion curve, also yields the leading term in the roughness-induced contribution to the van der Waals force for large ($\frac{l}{a}$) with semiquantitative accuracy.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnantioselective synthesis of PsiA.beta., a sporogenic metabolite of Aspergillus nidulansPaul Mazur and Koji NakanishiCite this: J. Org. Chem. 1992, 57, 3, 1047–1051Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://pubs.acs.org/doi/10.1021/jo00029a058https://doi.org/10.1021/jo00029a058research-articleACS PublicationsRequest reuse permissionsArticle Views1003Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
We develop the theory of the temperature variation of surface-spin-wave frequencies in the semi-infinite Heisenberg ferromagnet, for modes with wavelength sufficiently short that exchange interactions provide the dominant contribution to the excitation energy. Magnon-magnon interactions are the source of the temperature variation of the surface-spin-wave energies, and our attention is directed toward the leading contribution in the limit of low temperatures. We find a ${T}^{\frac{5}{2}}$ correction to the $T=0$ spin-wave frequencies, so the leading term exhibits the same temperature variation as found for bulk spin waves.
