A vibrational study of the CD2 stretching bands of selectively deuterated palmitic and stearic acids

The C-D stretching regions of the infrared and Raman spectra of 14 different palmitic and stearic acids containing isolated CD₂ groups are reported. Anomalous behaviour is observed when substitution occurs near the terminal methyl group, which behaviour can not be explained in terms of crystal field effects.     

心磷脂-细胞色素C体系CD谱的研究

 线粒体内膜中含有特异的心磷脂是细胞色素C氧化酶活性的必需脂。本工作测定了心磷脂脂质体对细胞色素C溶液园二色(CD)谱的影响,发现心磷脂可引起血色素铁的氧化,并使其轴向配位场强的对称性下降。提示心磷脂可能参与酶和底物之间的电子转移过程。     

寡聚脱氧核苷酸d(G-C)_3的激光喇曼谱及其分析

用改进的固相磷酰三酯法合成了oligo-d(G-C)_3。以氩离子激光为激发光源,波长488nm.,在室温条件下,分别测定了纯化后的oligo-d(G-C)_3和其组分单体5’-dGMP和5’-dCMP的激光喇曼谱。观察到被测定的物质在300-2500cm~(-1)频率区间,各自都有其特征的谱形和喇曼峰。5’-dGMP和5’-dCMP谱中大多数特征峰在寡聚体的谱中消失,而在oligo-d(G-C)_3谱中出现了几处新的喇曼峰。经查证,峰832,851和899cm~(-1)系糖-磷酸主链的特征喇曼峰,另外几处峰与DNA的构象有关。实验结果表明oligo-d(G-C)_3在水溶液中(室温)主要以B-构象存在。     

光敏反应对过氧化氢酶的影响

光氧化反应中,纯过氧化氢酶活性受光敏化剂血卟啉Ⅳ和核黄素的抑制。随光敏化剂浓度增高及照光时间延长,抑制程度加大。酶与光敏化剂反应后吸收光谱位移,峰形改变。紫外差示吸收光谱出现229nm负峰(血卟啉)和236—240nm峰(核黄素)。结果表明酶活的抑制与其蛋白构象的变化相关。     

A comparison of neural networks and partial least squares for deconvoluting fluorescence spectra

This article compares backpropagation neural networks (BNN) with partial least squares (PLS) techniques in terms of their ability to deconvolute fluorescence spectra. Both actual experimental and simulated spectral data are studied for 2 binary systems. These systems consist of mixtures of tryptophan and tyrosine, and NADH and tryptophan over a total concentration range of 10(-7) to 10(-4) M. It is shown that BNN is superior to PLS for both systems.     

An Escherichia coli plasmid-based, mutational system in which supF mutants are selectable: Insertion elements dominate the spontaneous spectra

A new system is described to determine the mutational spectra of mutagens and carcinogens in Escherichia coli; data on a limited number (142) of spontaneous mutants is presented. The mutational assay employs a method to select (rather than screen) for mutations in a supF target gene carried on a plasmid. The E. coli host cells (ES87) are lacI⁻ (am26), and carry the lacZΔM15 marker for α-complementation in β-galactosidase. When these cells also carry a plasmid, such as pUB3, which contains a wild-type copy of supF and lacZ-α, the lactose operon is repressed (off). Furthermore, supF suppression of lacl^um26 results in a lactose repressor that has an uninducible, lacl^S genotype, which makes the cells unable to grow on lactose minimal plates. In contrast, spontaneous or mutagen-induced supF⁻ mutations in pUB3 prevent suppresion of lacl^am26 and result in constitutive expression of the lactose operon, which permits growth on lactose minimal plates. The spontaneous mutation frequency in the supF gene is 0.7 and 1.0 × 10⁻⁶ without and with SOS induction, respectively. Spontaneous mutations are dominated by large insertions (67% in SOS-uninduced and 56% in SOS-induced cells), and their frequency of appearance is largely unaffected by SOS induction. These are identified by DNA sequencing to be Insertion Element: IS1 dominates, but IS4, IS5, gamma-delta and IS10 are also obtained. Large deletions also contribute significantly (19% and 15% for - SOS and +SOS, respectively), where a specific deletion between a 10 base pair direct repeat dominates; the frequency of appearance of these mutations also appears to be unaffected by SOS induction. In contrast, SOS induction increases base pairing mutations (13% and 27% for -SOS and +SOS, respectively), The ES87/pUB3 system has many advantages for determining mutational spectra, including the fact that mutant isolation is fast and simple, and the determination of mutational changes is rapid because of the small size of supF.     

Probing nucleosome core secondary structure before and after α-chymotrypsin treatment by raman spectroscopy and thermal denaturation

Nucleosome cores were digested with α-chymotrypsin until histone H3 was degraded to a partial histone, CP1. As we reported previously, cleavage occurred at leucine 20 to H3 and resulted in an increase in circular dichroism between 265 to 285 nm. Some modest core unfolding was also observed as determined by a small decrease in the sedimentation coefficient. Studies reported here deal with the analysis of core secondary structure and subsequent perturbation caused by treatment with α-chymotrypsin. Raman spectroscopy indicated that chymotryptic treatment promoted a change in the conformational environment of a population of core histone tyrosines. In addition, a shift from B-form to an intermediate B- or A-form was observed for core DNA. High-resolution thermal denaturation was used to determine alterations in the stabilization of core DNA related to perturbation of the core histones. Brief chymotryptic treatment indicated changes in both pre-melt and irreversible transitions.     

C andH NMR spectroscopy as a tool in the configurational analysis of iridoid glucosides

The ¹³C NMR data of 51 iridoid glucosides or glucoside acetates are tabulated. The collection includes 20 pairs of C-6, C-7 or C-8 epimers. Three parameters in using the data for the configurational assignment of 6-O-substituents are given. The chemical shift for C-9 in a range of substituted compounds is shown to be numerically related to the stereochemistry at C-8. This allows the determination of the configuration at this centre for most types of substitution patterns by calculation of the C-9 shift using increments for each substituent. Such increments are given for 25 substituents in three different solvents. A method for simulation of spectra of unknown iridoid glucosides is presented. By this method, the structures of five novel iridoid glucosides have been elucidated, and that of tecomoside has been revised. The methods used to assign the configurations to C-6 and C-8 epimeric iridoid glucosides by ¹H NMR spectroscopy are discussed and a table with selected data is presented. It is suggested that the structures in the literature for ajugol and myoporoside should be interchanged. Consequently, Horeau's method has failed in these instances. Finally, the differences in the ¹³C NMR spectra of pairs of C-6 and C-8 epimeric iridoid glucosides have been interpreted as originating from cis/trans-interactions.     

On the role of ß-carotene in the reaction center chlorophyll a antennae of photosystem I

Absorption and low temperature fluorescence emission spectra were measured on chloroplast thylakoids and on purified reaction center chlorophyll a-protein complexes of photosystem I, CP-a₁. A clear association between the presence of ß-carotene and the occurrence of far red absorbing and emitting chlorophyll a components of the reaction center antennae of photosystem I was demonstrated. For this study chloroplasts and CP-a₁ were obtained from normal and carotenoid deficient plant material of various sources. The experimental material included 1) lyophilized pea chloroplasts extracted with petroleum ether, 2) the carotenoid deficient mutant C-6E of Scenedesmus obliquus and 3) wheat chloroplasts derived from normal and SAN-9789 treated plants. Removal of carotenoids, most likely principally ß-carotene, caused a loss of long wavelength absorbing chlorophylls in chloroplasts and purified CP-a₁, and the loss or diminution of the long wavelength peak seen in the low temperature fluorescence emission spectrum. This association between ß-carotene and special chlorophyll a forms may explain both the photoprotective and antenna functions ascribed to ß-carotene. In the absence of carotenoids in wheat and in the Scenedesmus mutant, the chlorophyll a antenna of photosystem I was extremely photosensitive. A triplet-triplet resonance energy transfer from chlorophyll a to ß-carotene and a singlet-singlet energy transfer from excited ß-carotene to chlorophyll would explain the photoprotective and antenna functions, respectively. The role of this association in determining some of the fluorescence properties of photosystem I is also discussed.     

A general synthesis of long chain ω- and (ω-1)-hydroxy fatty acids

A method for the synthesis of long chain fatty acids substituted at the ω and ω-1 positions has been developed. The key step is the isomerization of the triple bond of an alkyn-1-ol from an internal position in the chain to the free terminus with a new, convenient reagent, sodium aminopropylamide (NaAPA). Standard functional group manipulations i.e., Jones oxidation, esterification and hydroboration of the triple bond are used to prepare ω-hydroxy fatty esters. The generality of the method is illustrated with syntheses of ω-hydroxy fatty esters with 24, 26, 28 and 30 carbon chains.In the 24 carbon series, hydration of the terminal triple bond of alkynoic ester 4a followed by reduction gave the (ω-1)-hydroxy ester.