Direct observation of the iron binding sites in a ferritin

X-Ray analysis of the ferritin of Escherichia coli (Ec-FTN) and of Ec-FTN crystals soaked in (NH₄)₂Fe(SO₄)₂ has revealed the presence of three iron-binding sites per subunit. Two of these form a di-iron site in the centre of the subunit as has been proposed for the ‘ferroxidase centres’ of human ferritin H chains. This di-iron site, lying within the 4-alpha-helix bundle, resemble those of ribonucleotide reductase, methane monoxygenase and haemerythrin. The third iron is bound by ligands unique to Ec-FTN on the inner surface of the protein shell. It is speculated that this state may represent the nucleation centre of a novel type of Fe(III) cluster, recently observed in Ec-FTN.     

-Dystroglycan deficiency correlates with elevated serum creatine kinase and decreased muscle contraction tension in golden retriever muscular dystrophy

The dystrophin—glycoprotein complex was examined in dystrophin-deficient dogs with golden retriever muscular dystrophy (GRMD) using immunoblot and immunofluorescence analysis. The dystrophin-associated proteins were substantially reduced in muscle from dogs with GRMD. Interestingly, regression analysis revealed a strong correlation between the amount of -dystroglycan and serum creatine kinase levels and the contraction tension measured for a given peroneus longus muscle.     

Polypeptide composition,assembly and phosphorylation patterns of the photosystem II antenna system of Chlamydomonas reinhardtii

In recent years major progress has been made in describing the gene families that encode the polypeptides of the light-harvesting antenna system of photosystem II (PSII). At the same time, advances in the biochemical characterization of these antennae have been hampered by the high degree of similarity between the apoproteins. To help interpret the molecular results, we have re-examined the composition, the assembly and the phosphorylation patterns of the light-harvesting antenna of PSII (LHCII) in the green alga Chlamydomonas reinhardtii Dang, using a non-Tris SDS-PAGE system capable of resolving polypeptides that differ by as little as 200 daltons. Research to date has suggested that in C. reinhardtii the LHCII comprises just four polypeptides (p11, p13, p16 and p17), and CP29 and CP26 just one polypeptide each (p9 and p10, respectively), i.e. a total of six polypeptides. We report here that these antenna systems contain at least 15 polypeptides, 10 associated with LHCII, 3 with CP29, and 2 with CP26. All of these polypeptides have been positively identified by means of appropriate antibodies. We also demonstrate substantial heterogeneity to the pattern of in-vitro phosphorylation, with major differences found among members of closely spaced and immunologically related polypeptides. Most intriguing is the fact that the polypeptides that cross-react with the anti-type 2 LHCII antibodies of higher plants (p16, and to a lesser extent p11) are not phosphorylated, whereas in higher plants these are the most highly phosphorylated polypeptides. Also, unlike in higher plants, CP29 is heavily phosphorylated. Phosphorylation does not appear to have any effect on the mobility of polypeptides on fully denaturing SDS-PAGE gels. To learn more about the accumulation and organization of the light-harvesting polypeptides, we have also investigated a chlorophyll b-less mutant, cbn1-48. The LHCII is almost completely lost in this mutant, along with at least some LHCI. But the accumulation of CP29 and CP26 and their binding to PSII core complexes, is relatively unaffected. As expected, the loss of antenna polypeptides is accompanied by a reduction of the size of large reaction-center complexes. Following in-vitro phosphorylation the number of phosphorylated proteins is greatly increased in the mutant thylakoids compared to wildtype thylakoids. We present a model of the PSII antenna system to account for the new polypeptide complexity we have demonstrated.This work was supported by National Institute of Health grant GM22912 to L.A.S. We would like to thank Anastasios Melis for helpful discussions.     

A 43 kDa protein inserted at the plasma membrane-cytoskeleton interface in rumen entodiniomorphid ciliates

Summary The P-43 ofEudiplodinium and homologous proteins in three other entodiniomorphid species, free-living ciliates, flagellates, and HeLa cells, were identified at the plasma membrane-cytoskeleton interface. Proteins cross-reacting with MAb B6 were also located at the ciliary inner surface of the plasma membrane. Due to the strong adhesion of the plasma membrane to the underlying cytoskeleton, classical extraction with detergents, urea, NaOH, and PTA, failed to separate the two components completely. However, the extraction properties of P-43, associated with its membrane-cytoskeleton interactive functions, suggest that this unglycosylated protein may present some analogies with proteins of the intermediate filaments. Their ubiquity and localization suggest that P-43 and MAb B6 crossreacting proteins may not be strictly epiplasmic but could be amphitropic proteins, strongly anchored to both the plasma membrane and the underlying microfilament framework, via protein-protein binding or by direct insertion in the lipid bilayer.Abbreviations BSA bovine serum albumin - Con A concanavalin A - EDTA ethylene diamine tetraacetic acid - EM electron microscopy - IF intermediate filaments - MAb monoclonal antibody - MET 2-mercaptoethanol - MW molecular weight - PAb polyclonal antibody - PBS phosphate buffered saline - PMSF phenylmethylsulfonyl fluoride - PTA phosphotungstic acid - SDS sodiumdodecyl sulfate - TAME Na-p-tosyl-arginine methyl ester - TLCK Na-p-tosyl-lysine chloromethyl ketone     

Light-harvesting chlorophyll a-b complex requirement for regulation of Photosystem II photochemistry by non-photochemical quenching

Recently, it has been suggested (Horton et al. 1992) that aggregation of the light-harvesting a-b complex (LHC II) in vitro reflects the processes which occur in vivo during fluorescence induction and related to the major non-photochemical quenching (qE). Therefore the requirement of this chlorophyll a-b containing protein complex to produce qN was investigated by comparison of two barley mutants either lacking (chlorina f2) or depressed (chlorina¹⁰⁴) in LHC II to the wild-type and pea leaves submitted to intermittent light (IL) and during their greening in continuous light. It was observed that qN was photoinduced in the absence of LHC II, i.e. in IL grown pea leaves and the barley mutants. Nevertheless, in these leaves qN had no (IL, peas) or little (barley mutants) inhibitory effect on the photochemical efficiency of Q_A reduction measured by flash dosage response curves of the chlorophyll fluorescence yield increase induced by a single turn-over flash During greening in continuous light of IL pea leaves, an inhibitory effect on Q_A photoreduction associated to qN developed as Photosystem II antenna size increased with LHC II synthesis. Utilizing data from the literature on connectivity between PS II units versus antenna size, the following hypothesis is put forward to explain the results summarized above. qN can occur in the core antenna or Reaction Center of a fraction of PS II units and these units will not exhibit variable fluorescence. Other PS II units are quenched indirectly through PS II-PS II exciton transfer which develops as the proportion of connected PS II units increases through LHC II synthesis.     

Microelectrode-recorded development of the symplasmic autonomy of the sieve element/companion cell complex in the stem phloem of Lupinus luteus L.

From the cambial stage onwards, the symplasmic autonomy of sieve element/companion cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intracellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multicellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.Abbreviations LYCH Lucifer Yellow CH - membrane potential - PMF proton-motive force - PP phloem parenchyma cell - SE/CC-complex sieve element/companion cell complex - SR-G sulphorhodamine G     

质体醌重组的D1／D2／Cytb559复合物的荧光衰减动力学和光破坏作用

光系统Ⅱ反应中心Ｄ１／Ｄ２／Ｃｙｔｂ５５９ 在分离纯化过程中失去了电子受体ＱＡ 和ＱＢ,人工合成的质体醌可以与Ｄ１／Ｄ２／Ｃｙｔｂ５５９ 复合物发生重组。癸基质体醌（ＤＰＱ）与Ｄ１／Ｄ２／Ｃｙｔｂ５９９ 复合物的重组导致该复合物的荧光强度下降及发射光谱蓝移,同时两个与光化学活性相关的长寿命（２４ ｎｓ和７３ ｎｓ）荧光衰减组分占整个荧光的百分数下降,这些结果表明ＤＰＱ作为Ｐｈｅｏ－ 的电子受体,限制了Ｐ６８０＋ ·Ｐｈｅｏ－ 的电荷重组。ＤＰＱ 的加入对Ｄ１／Ｄ２／Ｃｙｔｂ５５９复合物中Ｃｈｌａ 分子的光破坏敏感性影响不大,但β－胡萝卜素在加入ＤＰＱ 之后可以被光照破坏,这个过程可能与β－胡萝卜素的生理功能相关。     

利用林木边行优势营造杨树速生丰产林的试验研究──林农复合生态经济系统的新模式

利用林木边行优势营造杨树速生丰产林的试验研究──林农复合生态经济系统的新模式许鸿儒,刘金声（辽宁省黑山县林业局,１２１４００）（辽宁省林业厅造林处,沈阳１１０００１）范学文（辽宁省锦西市林业局,１２１５００）ＰｌａｎｔｉｎｇｏｆＦａｓｔ－Ｇｒｏｗｉｎ...     

Cytogenetical localization of Zygotic hybrid rescue (Zhr), a Drosophila melanogaster gene that rescues interspecific hybrids from embryonic lethality

Hybrid females from crosses between Drsophila melanogaster males and females of its sibling species, D. simulans, D. mauritiana, or D. sechellia die as embryos. This lethality is believed to be caused by incompatibility between the X chromosome of D. melanogaster and the maternal cytoplasm. Zygotic hybrid rescue (Zhr) prevents this embryonic lethality and has been cytogenetically mapped to a proximal region of the X chromosome of D. melanogaster, probably in the centromeric heterochromatin. We have carried out high resolution cytological mapping of Zhr using deficiencies and duplications of the X heterochromatin. Deletions of the Zhr ⁺ gene from the hybrid genome exhibit the Zhr phenotype. On the contrary, addition of the wild-type gene to the hybrid genome causes embryonic lethality, regardless of sex. The Zhr locus has been narrowed down to the region covered by Dp(1;f)1162 but not covered Dp(1;f)1205, a chromosome carrying a duplication of heterochromatin located slightly distal to the In(1)sc ⁸ heterochromatic breakpoint.     

Inhibition of mugineic acid-ferric complex uptake in barley by copper, zinc and cobalt

The interfering effects of copper, zinc, and cobalt on the uptake of mugineic acid-ferric complex were studied in barley ( Hordeum vulgare , cv. Minorimugi) grown in nutrient solution. Short-term uptake experiments of 3 h were performed utilizing both ionic and mugineic acid-complex forms of each metal at two different concentrations. Copper was most effective in decreasing iron uptake when added in an ionic form at either concentration. The inhibition order at higher concentrations followed Cu(II) > Zn(II) ≥ Co(II), Co(III), which is consistent with the stability constants of these metal complexes with mugineic acid. The displacement of iron from its mugineic acid complex by these metals is suggested as a probable explanation for the decreased iron uptake. The inhibitory effect of metal complexes with mugineic acid on iron uptake was only found in cases with higher concentrations of Cu(II) and Zn(II) complexes. Deformation of the specific iron transport system in the plasma membrane due to their adsorption may be responsible for this effect.