Further characterization of ribosome binding to thylakoid membranes

Previous work indicated more polysomes bound to pea (Pisum sativum cv Progress No. 9) thylakoids in light than in the dark, in vivo (LE Fish, AT Jagendorf 1982 Plant Physiol 69: 814-825). With isolated intact chloroplasts incubated in darkness, addition of MgATP had no effect but 24 to 74% more RNA was thylakoid-bound at pH 8.3 than at pH 7. Thus, the major effect of light on ribosome-binding in vivo may be due to higher stroma pH. In isolated pea chloroplasts, initiation inhibitors (pactamycin and kanamycin) decreased the extent of RNA binding, and elongation inhibitors (lincomycin and streptomycin) increased it. Thus, cycling of ribosomes is controlled by translation, initiation, and termination. Bound RNA accounted for 19 to 24% of the total chloroplast RNA and the incorporation of [³H]leucine into thylakoids was proportional to the amount of this bound RNA. These data support the concept that stroma ribosomes are recruited into thylakoid polysomes, which are active in synthesizing thylakoid proteins.     

世居及移居高原青少年最大有氧能力的特征

本文报道海拔３４１７ｍ和４２８０ｍ地区世居藏族和移居汉族青少年运动状态下心肺功能的对比研究。结果显示：３４１７ｍ和４２８０ｍ世居藏族的最大氧耗量、无氧阈值及最大心输出量都明显大于汉族,血氧饱和度（Ｓａｏ２）随运动负荷的增加而降低。海拔３４１７ｍ藏、汉族的△Ｓａｏ２分别为７．４６％和１０．０３％,４２８０ｍ处为８．５７％和１３．７５％,最大心率随海拔升高而下降。研究提示,藏族青少年有较高的最大有氧能力,反映了他们对低氧环境的适应优势。     

A Purified Zinc Protease of Pea Chloroplasts,EP1, Degrades the Large Subunit of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase

A previously reported endopeptidase (EP1) from pea chloroplasts was purified over 11,000-fold using a four-step protocol involving ultrafiltration, sucrose gradient centrifugation, isoelectric focusing, and high performance liquid chromatography gel filtration. The enzyme was determined to be a metalloprotease requiring bound Zn2+ and added Mg2+ or Ca2+ for proper activity. Its localization in the stroma of pea chloroplasts was confirmed by demonstrating its insensitivity to thermolysin when the envelope was intact. A contaminating serine protease that attacks EP1 was found. The contaminating protease was inhibited by 4-(2-aminoethyl)-benzenesulfonyl fluoride, but not by o-phenanthroline, whereas EP1 sensitivities were the reverse. EP1 is able to hydrolyze the large subunit of native ribulose-1,5-bisphosphate carboxylase/oxygenase under physiological conditions.     

Synthesis of subunit III of CF0 by thylakoid-bound polysomes from pea chloroplasts

Summary Wahsed thylakoid membranes from pea chloroplasts incorporate label from (³⁵S)-methionine into protein when supplemented with S-30 soluble factors from E. coli. One of the products associated with the thylakoids is soluble in butanol, precipitated by ether and has an apparent molecular mss of 8200D on urea-lithium dodecyl sulphate (LDS) polyacrylamide gels. In addition, the protein covalently binds dicyclohexylcarbo-diimide (DCCD) which causes it to migrate as two slower forms on gels. Based on these criteria we establish that the proteolipid or subunit III of CF₀ (the intrinsic sector of the ATPase complex) is synthesized by the thylakoid bound polysomes.     

Factors permitting prolonged translation by isolated pea chloroplasts

The following parameters were found to prolong the time-course of translation by isolated pea (Pisum sativum, cv Progress No. 9) chloroplasts: addition of other amino acids (an effect synergistic with sufficient free Mg²⁺), use of lower light intensities, and additions of inorganic phosphate and ATP. In a chloroplast system which includes these parameters, active translation usually extends to almost an hour. The total amount of leucine incorporated is routinely 60 to 100 nanomoles/milligram chlorophyll and often 200 nanomoles/milligram chlorophyll. Accurate estimation of the amount of amino acid incorporated depends on supplying the labeled amino acid at a concentration sufficient to overcome isotope dilution effects from endogenous pools. Approximately 39 thylakoid and 60 stroma polypeptides were visible on autoradiographs after labeling with [³⁵S]methionine. Label in a few of the polypeptide bands was increased or decreased by specific changes in the reaction conditions. Due to the long period of activity and the large number of labeled products, this chloroplast system should be useful for future studies of chloroplast translation.     

Permeability of chloroplast envelopes to mg: effects on protein synthesis

When suspended in media lacking free Mg²⁺, chloroplasts from young pea plants (Pisum sativum CV Progress No. 9) lose 25 to 75% of their stromal Mg²⁺ content to the medium, without breakage. This effect amounts for the inhibition of protein synthesis in the dark by ATP in excess of the Mg²⁺ provided, since free ATP chelates Mg²⁺. The rate of loss is from 1 to 4.5 microgram-atoms Mg²⁺/milligram Chl/hour; and depleted chloroplasts take up Mg²⁺ from the medium at even faster rates, to a total amount not much more than that present originally (0.8 to 1.8 microgram-atoms/milligram Chl with an average of 1.33 ± 0.32 μg-atoms/mg Chl). Leakage is completely prevented by 0.25 to 0.40 millimolar external Mg²⁺. Addition of Mg²⁺ at a level sufficient to prevent leakage from intact chloroplasts results in approximately 20% stimulation in light-driven protein synthesis.     

Arginine modifiers as energy transfer inhibitors in photophosphorylation.

Photophosphorylation by spinach chloroplasts is inhibited after they have been incubated in the dark with either phenylglyoxal or butanedione. Inhibition by phenylglyoxal is strongest when N-ethylmorpholine is the buffer used during the incubation; that by butanedione requires the presence of borate as buffer. The inhibitions are not reversed by simply washing out the inhibitor, suggesting that a covalent modification of one or more arginine residues is responsible. This is supported by the reversibility of the butanedione inhibition if both the inhibitor and borate buffer are removed. ATPase of the chloroplasts, and of extracted protein, is inhibited, whether activated by trypsin or by heating. This indicates that arginine residues of the coupling factor are the probable major site(s) for attack by these modifiers, leading to the observed inhibitions.     

Isolation and composition of the subunits of spinach chloroplast coupling factor protein.

A more convenient method for preparing large amounts of spinach chloroplast coupling factor is described, in which centrifugation of the EDTA-extracted chloroplasts is replaced by batchwise adsorption on DEAE-cellulose followed by filtration through Miracloth. Methods have been developed to purify the subunits from coupling factor dissociated by sodium dodecyl sulfate, involving hydroxylapatite chromatography followed by gel filtration with the detergent still present. The amino acid composition of the subunits purified by these methods was determined, with some differences noted in values for cysteine, tyrosine, phenylalanine, and methionine compared to previously published values. The stoichiometry of the subunits was estimated as 2:2:1:1:2 from their relative adsorption of dye after gel electrophoresis, compared to dye adsorbed by known amounts of the purified subunits. Estimates of subunit stoichiometry are rounded off to nearest whole numbers; actual preparations of coupling factor usually show less than complete amounts of the two smallest subunits.     

The phylogeny of the ant tribe Formicini (Hymenoptera: Formicidae) with the description of a new genus

Abstract. The holarctic ant tribe Formicini is revised, the new genus Bajcaridris described, and possible phylogenetic relationships are discussed. The subgenus Iberoformica is synonymized with Formica. A synopsis, diagnosis and keys to the genera are provided.