Patterns of sequence variation in the mitochondrial D-loop region of shrews

Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews (genus Sorex) for the region between the tRNA(Pro) and the conserved sequence block-F revealed variable numbers of 79-bp tandem repeats. These repeats were found in all 19 individuals sequenced, representing three subspecies and one closely related species of the masked shrew group (Sorex cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an adjacent 76-bp imperfect copy of the tandem repeats. One individual was heteroplasmic for length variants consisting of five and seven copies of the 79-bp tandem repeat. The sequence of the repeats is conducive to the formation of secondary structure. A termination-associated sequence is present in each of the repeats and in a unique sequence region 5' to the tandem array as well. Mean genetic distance between the masked shrew taxa and the pygmy shrew was calculated separately for the unique sequence region, one of the tandem repeats, the imperfect repeat, and these three regions combined. The unique sequence region evolved more rapidly than the tandem repeats or the imperfect repeat. The small genetic distance between pairs of tandem repeats within an individual is consistent with a model of concerted evolution. Repeats are apparently duplicated and lost at a high rate, which tends to homogenize the tandem array. The rate of D- loop sequence divergence between the masked and pygmy shrews is estimated to be 15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid sequence evolution in shrews may be due either to their high metabolic rate and short generation time or to the presence of variable numbers of tandem repeats.      

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。     

Analysis of fluorescence induction in thylakoids with the method of moments reveals two different active Photosystem II centres

There is presently a debate concerning the number of phases in fluorescence induction and on the identification of the several possible heterogeneities in PS II centres. However, the usual methods of analysis present numerical problems, including a lack of robustness (robustness being defined as the ability to give the correct answer in the presence of distortions or artefacts). We present here the adaptation of the method of moments, which was developed for robustness, to the analysis of fluorescence induction. We were thus able to identify three phases in the fluorescence induction in the presence of DCMU. The slowest phase was attributed to the centres inactive in plastoquinone reduction by using duroquinone as electron acceptor. In order to compare fluorescence with and without DCMU, we introduced the rate of photochemistry, defined as the product of the area times the rate constant of an exponential. This quantity is invariant for a given centre no matter what the size of the electron acceptor pool is. The two fastest phases in the presence of DCMU were attributed to active centres because their rate of photochemistry was the same as that of the plastoquinone-reducing phases in the absence of DCMU. Because their reduction of plastoquinone showed different kinetics, these two types of active centres were either separated by more than 250 nm or were associated with discrete plastoquinone pools having restricted diffusion domains.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DMBQ 2,5-dimethyl-p-benzoquinone - MOPS 3-[N-Morpholino]propanesulphonic acid - PpBQ Phenyl-p-benzoquinone     

Cytochrome components of plant microsomes.

The electron transport components of the microsomal fraction of cauliflower buds and mung bean hypocotyls were investigated using split-beam and dual wavelength spectrophotometry under a variety of reducing conditions. Cauliflower microsomes were found to contain an ascorbate-reducible component, termed cytochrome b-559.5 [E'0 = +135 +/- 20 mV; lambdamax (reduced minus oxidised) = 559.5, 527 and 429 nm at 23 degrees C], cytochrome b5 [E'0 = -20 +/- 20 mV; lambdamax (reduced minus oxidised) = 556, 526 and 425 nm at 23 degrees C], cytochromes P-450 and P-420. On the basis of binding studies with ethyl isocyanide, degradation of cytochrome P-450 to P-420, redox potential, aniline binding, and relative rates of reduction by NADPH and NADH, it is suggested that the cytochrome P-450 system is analogous to that mammalian microsomes. Other components, reducible only by dithionite, may also be present. Mung bean microsomes were found to contain an ascorbate-reducible component, termed cytochrome b-562 [E'0 = +120 +/- 20 mV; lambdamax (reduced minus oxidised) = 562, 528 and 430 nm at 23 degrees C], cytochrome b5, and a low potential component which was reducible only by sodium dithionite. No cytochrome P-450 or P-420 could be detected. A general method of analysis of the cytochromes was developed and applied to the microsomes from a variety of plant sources. The results indicate that large variations, both in type and amount of components, occur between the microsomes from different plant materials.     

The separation and distribution of simple and condensed leucoanthocyanins of the tea plant (Camellia sinensis L.)

1. Leucoanthocyanin monomers of high mobilities in aqueous solvents on thinlayer chromatograms, assumed to be structurally simple, were characteristic of mature bulky tissues, whereas members of lower mobility were confined to young vegetative and floral tissues. 2. Flavylogens were separated by gel filtration on Sephadex columns into monomeric, oligomeric and polymeric fractions. 3. The polymeric fraction from young brown stems was heterogeneous, one-half having a molecular weight of about 3400, one-third a molecular weight between 3600 and 17000, and the remainder a molecular weight of over 17000. 4. Leaves had low flavylogen concentrations; only monomers were present. Stem tissues were rich in polymers, which increased with the age of the young stem and decreased inwards through the wood. The maximal flavylogen concentrations were in the phloem and cambium from mature stems, where all three fractions were richly present. The periderm tissue and, to a lesser extent, the seed coat were characterized by a very high polymer/monomer ratio, exhibiting a much higher degree of polymerization than the wood. Root tissues contained high concentrations of monomers. 5. In general, there was an inverse correlation between the extent of polymerization and the complexity of the monomers present. 6. The results are in favour of the thesis that the function of the flavanols is, after polymerization to condensed tannins, to impregnate dead structural tissues and thereby to protect them from infection and decay.     

The kinetics and thermodynamics of the reduction of cytochrome c by substituted p-benzoquinols in solution

1. The mechanisms by which p-benzoquinol and its derivatives reduce cytochrome c in solution have been investigated. 2. The two major reductants are the species QH- (anionic quinol) and Q.- (anionic semiquinone). A minor route of electron transfer from the fully protonated QH2 species can also occur. 3. The relative contributions of these routes to the overall reduction rate are governed by pH, ionic strength and relative reactant concentrations. 4. For a series of substituted p-benzoquinols, the forward rate constant, k1, of the anionic quinol-mediatd reaction is related to the midpoint potential of the QH-/QH. couple involved in the rate-limiting step, as predicted by the theory of Marcus for outer-sphere electron transfer reactions in a bimolecular collision process. 5. A mechanism for the biological quinol oxidation reactions in mitochondria and chloroplasts is proposed based upon the findings with these reactions in solution.