C4 photosynthesis in Spartina townsendii at low and high temperatures

The metabolism of ¹⁴CO₂ in the cool temperate saltmarsh grass Spartina townsendii was investigated in plants grown in their natural habitats at two temperatures. Both in the spring at 10°C and in the late summer at 25°C radioactivity was initially incorporated into the organic acids malate and aspartate and then transferred to 3-phosphoglycerate in the manner characteristic of the C₄ pathway of photosynthesis. Metabolism was not disrupted at the lower temperature as in some C₄ plants. Radioactivity was transferred more slowly from malate into alanine, glycine and serine at 10°C, but sugars were labelled equally at both temperatures.     

湖北石松目植物的研究

石松目植物是蕨类植物中经济价值较高的一个类群,除孢子粉供铸造工业使用外,大部份种类供药用,有的种类为酸性土的指示植物。湖北石松种类比较丰富,历年来植物学工作者们在我省采集了大量标本,并对民间使用情况进行过调查,积累了不少有用     

Potentiation by calcium ions of the antithrombin III inhibition of thrombin

Calcium ions potentiated heparin-modulated antithrombin III inhibition of amidolysis catalysed by thrombin. Potentiation by calcium ions of heparin-independent antithrombin III inhibition of thrombin activity appeared to contribute to this effect. These results suggest a complex modulatory role for calcium ions in proteinase-catalysed reactions influenced by anti-proteinases and glycosaminoglycans.     

Size transformations of intermediate and low density lipoproteins induced by unesterified fatty acids

Plasma from individual human subjects is known to contain multiple discrete subpopulations of low (LDL) and intermediate (IDL) density lipoproteins that differ in particle size and density. The metabolic origins of these subpopulations are unknown. Transformation of IDL and larger LDL to smaller, denser LDL particles had been postulated to occur as a result of the combined effects of triglyceride hydrolysis and lipid transfer. However, the presence of multiple small LDL subspecies has been described in patients lacking cholesteryl ester transfer protein. We have characterized an alternative pathway in which size decrements in IDL or LDL are produced in the presence of unesterified fatty acids and a source of apolipoprotein (apo) A-I. Incubation of IDL or LDL subfractions with palmitic acid and either high density lipoproteins (HDL), apoHDL, or purified apoA-I gives rise to apoA-I, apoB-containing complexes that can dissociate into two particles, an apoB-containing lipoprotein with particle diameter 10-30 A smaller than the starting material, and a still smaller species (apparent peak particle diameter 140-190 A) containing lipid and apoA-I but no apoB. The newly formed IDL or LDL are depleted in phospholipid and free cholesterol with no change in apoB-100 as assessed by SDS gel electrophoresis. We hypothesize that this reaction may contribute to the formation of discrete IDL and LDL subpopulations of varying size during the course of hydrolysis of triglyceride-rich lipoproteins in plasma.     

Effects of serotonin1-like receptor agonists on autonomic neurotransmission.

Serotonin1A receptor agonists, 8-hydroxy-2-(di-n-propylamino)tetralin and 10-methyl-11-hydroxyaporphine, inhibited electrical stimulation-induced contraction of the guinea-pig ileum. These agonists also inhibited the pressor and tachycardiac responses to low frequency (0.25 Hz) but not to high frequency (2.0 Hz) electrical stimulation of the sympathetic nervous system in pithed rats. Serotonin1B receptor agonist RU 24969 inhibited pressor and tachycardiac responses to both low and high frequencies of stimulation in pithed rats. In the cat nictitating membrane, serotonin1A receptor agonists did not alter contractions elicited by electrical stimulation (0.1-3.0 Hz). Serotonin not only contracted the cat nictitating membrane but also facilitated contractile responses to low frequency (0.1-1.0 Hz) stimulation. The contractile effect of serotonin in the cat nictitating membrane was blunted by bretylium, methysergide, and ketanserin, but not by metoclopramide. The facilitatory effect of serotonin was antagonized by methysergide, but not by ketanserin, pindolol, propranolol, or metoclopramide. These results suggest that serotonin1A receptors modulate autonomic neurotransmission in the guinea-pig ileum and pithed rats, but not in the cat nictitating membrane. Serotonin contracts the cat nictitating mebrane via serotonin2 subtypes, while facilitating stimulated contractile responses through the serotonin1-like receptors.     

Paleolimnology of Qilu Hu,Yunnan Province,China

Qilu Hu is a large (A = 36.9 km²), shallow (z_max = 6.8 m) lake that lies at an elevation of 1797 m above msl on the Yunnan Plateau, southern China. Lake waters are hard (Mg = 3.2m eq L^–1, Ca = 1.3 meq L^–1 ), fresh (conductivity = 380 S cm ^–1), and productive (Secchi < 40 cm). An 11-m sediment core has a basal ¹⁴C age of 30960 ± 860 B.P. Sediments between 11 m and 6 m are high in % dry weight, rich in clay components Al₂O₃, Fe₂O₃, K₂O, MgO, and low in organic C (6.1%), carbonate-C (<1.0%), total N (<3.2 mg g^–1), and total S (<-1.7 mg g^–1). Diatoms and pollen indicate open-water conditions between 9.0 m and 6.0 m (1342011790 B.P.). Above 6.0 m, CaCO₃ and organic matter concentrations increase relative to clastics. The transition marks a change to shallow-water conditions as inferred from diatoms and pollen, and probably reflects a shift to drier climate. Uppermost (80-0 cm) red clays were deposited rapidly, probably as a consequence of recent (decades to centuries) riparian disturbances (e.g. agriculture, lake-bottom reclamation, urban development). Dates assigned to events in the Qilu Hu profile are tentative because of potential hard-water-lake error.     

Codon usage divergence of homologous vertebrate genes and codon usage clock

Summary This paper is concerned with the divergence of synonymous codon usage and its bias in three homologous genes within vertebrate species. Genetic distances among species are described in terms of synonymous codon usage divergence and the correlation is found between the genetic distances and taxonomic distances among species under study. A codon usage clock is reported in alphaglobin and beta-globin. A method is developed to define the synonymous codon preference bias and it is observed that the bias changes considerably among species.     

不同来源的肾综合征出血热病毒对Vero细胞的致病变作用

前文报道,肾综合征出血热病毒76-118株能使Vero细胞产生病变。本文报道76-118株和另11株不同来源的肾综合征出血热病毒(H537、A9、H5、R178、HB55、R22、Z10,沟3、L99、A16和J10)对Vero细胞的致病变作用(CPE )。其中除沟3株外,大部分毒株在感染Vero细胞后的第一代即可见明显的CPE。CPE的特点与76-118株相似,主要是感染细胞粘聚、融合,形成网状结构。CPE能被特异性抗HFRS病毒血清和型特异性单克隆抗体所中和抑制,但不能被特异性抗呼肠孤病毒Ⅲ型免疫血清所中和抑制。HFRS病毒对Vero细胞的致病变作用,对进一步研究HFRS病毒的某些生物学特性及实验方法等均有重要意义。     

(A-C-B) human proinsulin, a novel insulin agonist and intermediate in the synthesis of biosynthetic human insulin.

The hormone insulin is synthesized in the beta cell of the pancreas as the precursor, proinsulin, where the carboxyl terminus of the B-chain is connected to the amino terminus of the A-chain by a connecting or C-peptide. Proinsulin is a weak insulin agonist that possesses a longer in vivo half-life than does insulin. A form of proinsulin clipped at the Arg65-Gly66 bond has been shown to be more potent than the parent molecule with protracted in vivo activity, presumably as a result of freeing the amino terminal residue of the A-chain. To generate a more active proinsulin-like molecule, we have constructed an "inverted" proinsulin molecule where the carboxyl terminus of the A-chain is connected to the amino terminus of the B-chain by the C-peptide, leaving the critical Gly1 residue free. Transformation of Escherichia coli with a plasmid coding for A-C-B human proinsulin led to the stable production of the protein. By a process of cell disruption, sulfitolysis, anion-exchange chromatography, refolding, and reversed-phase high-performance liquid chromatography, two forms of the inverted proinsulin differing at their amino termini as Gly1 and Met0-Gly1 were identified and purified to homogeneity. Both proteins were shown by a number of analytical techniques to be of the inverted sequence, with insulin-like disulfide bonding. Biological analyses by in vitro techniques revealed A-C-B human proinsulin to be intermediate in potency when compared to human insulin and proinsulin. The time to maximal lowering of blood glucose in the fasted normal rat appeared comparable to that of proinsulin. Additionally, we were able to generate fully active, native insulin from A-C-B human proinsulin by proteolytic transformation. The results of this study lend themselves to the generation of novel insulin-like peptides while providing a simplified route to the biosynthetic production of insulin.