Magnetic interaction of manganese with pheophytin anion-radical and chlorophyll cation-radical in reaction centers of the photosystem II

The influence of Mn on saturation curves of ESR spectra of Ph(-) and P(+)(680) at 1-200K in samples with different content of Mn has been studied. An analysis of these data and those on photoinduced changes of fluorescence yield of chlorophyll leads to the conclusion that the Mn-containing centre in Photosystem 2 is a cluster of 4 Mn atoms, two of which can be replaced by Mg(2+) or any other divalent metal. The distances between Mn Na Ph as well as between Mn and P(680) have been estimated.     

Changes in foliage distribution with relative irradiance and tree size: Differences between the saplings ofAcer platanoides andQuercus robur

Dependencies of foliage arrangement and structure on relative irradiance and total height (TH) were studied in saplings ofAcer platanoides andQuercus robur. The distribution of relative foliar area and dry weight (leaf area and weight in a crown layer per total tree leaf area and weight, respectively) were examined with respect to relative height (RH, height in the crown per TH) and characterized by the Weibull function. The distributions of relative area and weight were nearly identical, and the differences between them were attributable to a systematic decline in leaf dry weight per area with increasing crown depth. Foliage distribution was similarly altered by tree size in both species; RH at foliage maximum was lower and relative canopy size (RCS, length of live crown per TH) greater in taller trees. However, the distribution was more uniform inA. platanoides than inQ. robur. Apart from the size effects, relative irradiance also influenced canopy structure; RCS increased inQ. platanoides and decreased inQ. robur with increasing irradiance. As crown architecture was modified by irradiance, foliage distribution was shifted upwards with decreasing irradiance inA. platanoides, but it was independent of irradiance inQ. robur. Higher foliage maximum at lower irradiance in more shade-tolerantA. platanoides is likely to contribute towards more efficient foliar display for light interception and increase the competitive ability of this species in light-limited environments. Consequently, these differences in crown architecture and foliage distribution may partly explain the superior behavior ofA. platanoides in understory.     

Evolution of the ATP-binding-cassette transmembrane transporters of vertebrates

The ATP-binding-cassette transmembrane transporters (ABC transporters) known from vertebrates belong to four major subfamilies: (1) the P- glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance regulators (CFTR); (3) the Tap proteins encoded with the major histocompatibility complex of mammals; and (4) the peroxisomal membrane proteins. Both Pgp and CFTR have a structure suggesting a past internal gene duplication; a phylogenetic analysis indicated that these duplications occurred independently, while an independent tandem gene duplication occurred in the case of the Tap family. Both the Pgp and Tap proteins show evidence of relationship to bacterial ABC transporters lacking internal duplication, and both are significantly more closely related to the HlyB and MsbA families of transporters from purple bacteria than they are to ABC transporters from nonpurple bacteria. The simplest hypothesis to explain this observation is that eukaryotic Pgp and Tap genes are descended from a mitochondrial gene or genes that were subsequently translocated to the nuclear genome. The Pgp genes of eukaryotes are characterized by a remarkable degree of convergent evolution between the ATP-binding cassettes of their N- terminal and C-terminal halves, whereas no such convergence is seen between the two halves of CFTR genes or between the duplicated Tap genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain not found in other ABC transporters apart from CFTR, showed high levels of both synonymous and nonsynonymous difference in comparisons among different mammalian species, suggesting that this region is a mutational hot spot.      

Evidence for the presence of β-lactamase inStreptomyces glaucescens and its inhibition by sodium clavulanate

Streptomyces glaucescens is shown to possess -lactamase activity which is inhibitable by clavulanate. This is important in regard to its use as a cloning host for enzymes of \-lactam biosynthesis.     

Energy requirement for foliage construction depends on tree size inyoung Picea abies trees

 The relationship between stand biomass production, and tree age and size is generally a curve with a maximum. To understand why wood production decreases in the final stages of stand development, the influence of increasing tree size on foliage chemical composition and substrate requirement for foliage construction in terms of glucose [CC, g glucose (g dry mass)^{–  1}] was investigated in the evergreen conifer Picea abies (L.) Karst. Because it was already known that irradiance affects both foliage morphology and chemistry in this species, and it was expected that the foliage in large overstory trees would intercept on average more light than that in saplings in understory, irradiance was measured in the sampling locations and included in the statistical models. CC of needles increased with increasing total tree height (TH) and was independent of relative irradiance. A major reason for increasing CC with increasing TH was a greater proportion of carbon-rich lignin in the needles in large trees. However, lignin did not fully account for the observed changes in CC, and it was necessary to assume that certain other carbon-rich secondary metabolites such as terpenes also accumulate in the foliage of large trees. Enhanced requirements for needle mechanical strength as evidenced by greater lignin concentrations in large trees were attributed to increased water limitations with increasing tree height. Because water relations may also control the sink capacities for assimilate usage, apart from the mechanical requirements, they may provide an explanation for the accumulation of other energetically expensive compounds in the needles as well. Biomass partitioning within the shoot was another foliar parameter modified in response to increasing tree size. The proportion of shoot axes, which serve to provide needles with mechanical support and to supply them with water, decreased with increasing TH. This may limit water availability in the needles, and/or manifest a lower water requirement of the needles containing proportionally more supporting and storage substances, and consequently, less physiologically active compounds such as proteins. Probably the same factors which caused CC of the needles to depend on TH, were also responsible for greater CC of the shoot axes in larger trees. These results collectively suggest that increasingly more adverse water relations with increasing tree size may provide a mechanistic explanation for the decline in foliar biomass and its functional activity during stand ageing. Received: 9 April 1996 / Accepted: 14 January 1997     

Immunochemical characteristics of the peroxidases of several mouse tissues]

Enzymes catalyzing peroxidase reaction of a lysosomal fraction in bone marrow, leucocytes, spleen, thyroid gland, stomach, kidney, heart, lungs, brain and skeletal muscle of mice were investigated by immunochemical methods. A high level of peroxidase activity was discovered in leucocytes, bone marrow, spleen, heart and lung, a lower activity appeared to be characteristic of liver, thyroid gland and kidney. The peroxidase activities in brain, skeletal muscle and stomach were low. The reaction of immunoprecipitation with myeloperoxidase-specific antiserum revealed considerable antigenic distinctions between the enzymes catalysing peroxidase reaction in various tissues of mice.     

Three-Dimensional Trabecular Alignment Model

The Shear-slip Mesh Update Method (SSMUM) is being used in flow simulations involving large but regular displacements of one or more boundaries of the computational domain. We follow up the earlier discussion of the method with notes on practical implementation aspects. In order to establish a benchmark problem for this class of flow problems, we define and report results from a two-dimensional viscous flow around a rotating stirrer in a square chamber. The application potential of the method is demonstrated in the context of biomedical design problem, as we perform an analysis of blood flow in a centrifugal left ventricular assist device, or blood pump, which involves a rotating impeller in a non-axisymmetric housing.