The Glycoprotein Composition of Peripheral Nervous System Myelin Subfractions

Two fractions were isolated by continuous density gradient centrifugation from total particulate matter of rabbit sciatic nerves: a minor fraction, B, consisting of small-sized membrane fragments and a major fraction, C, of characteristic multilayered myelin figures, with maxima at 0.33 and 0.58 M-sucrose, respectively. In comparison with C, fraction B was enriched in CNPase and alkaline phosphatase activities and the P0, 23K and Z proteins, but was virtually devoid of basic protein. The glycoprotein composition of all fractions was examined with four fluorescein isothiocyanate-labelled lectins (WGA, Con A, RCA-60, U.E.). These revealed the presence of six glycoproteins in all fractions with similar lectin binding capacities and molecular weights ranging from 35,500 to 16,000, of which P0 was the predominant component. Material found on the heavy side of fraction C was characterized by the presence of a multitude of glycoproteins which bound variable proportions of the four different lectins, suggesting substantial variations in their carbohydrate moieties. Their absence from the central portion of fraction C points to a location other than that of compact PNS myelin.     

A role for recombination in the production of "free-loader" lambda bacteriophage particles

Density-labeled crosses were performed with bacteriophage lambda under conditions which diminish DNA duplication. The production of viable phage containing fully conserved parental DNA was found to be dependent upon the action of the genetic recombination systems. The production of phage containing DNA with one newly synthesized chain was less dependent upon recombination. The production of phage with chromosomes both of whose chains were synthesized following infection show little, if any, dependence on recombination. One can speculate that some step in the maturation process of bacteriophage lambda is inseparable from the reduction of lambda DNA to the monomeric rods characteristic of lambda virions.     

Subcellular Distribution of Aspartate Transaminase,Alanine Amino Transferase,Glutamate Dehydrogenases,and Lactate Dehydrogenase in Tetrahymena*

SYNOPSIS. Mitochondria and peroxisomes were isolated from homogenates of Tetrahymena pyriformis by sedimentation through a sucrose gradient. Succinate dehydrogenase was used as a mitochondrial marker; catalase and isocitrate lyase were used to mark the peroxisomal fraction. Lactate dehydrogenase, glutamate dehydrogenase, and alanine aminotransferase were found only in the mitochondrial fraction. Aspartate transaminase was found in both mitochondrial and peroxisomal fractions.     

Carbon Dioxide and Temperature Gradielits in Baermann Funnel Extraction of Rotylenchulus reniformis

Vermiform Rotylenchulus reniformis were anesthetized in water by 10-40% CO₂ but were fully motile for 24 hours in water below 5% CO₂. When air containing 2.5% CO₂ was blown onto agar, nematodes accumulated at the point of highest CO₂ concentration. Nematodes also accumulated when chilling (0.2-1 C) of agar by the gas flow at the accumulation point was offset with heat from a fiber optic. In Baermann funnels containing R. reniformis in silt loam and sandy clay loam soils, CO₂ in funnel water increased during 24 hours from 0 to ca. 1%; more CO₂ accumulated below the soil layer than above. Bubbling air with 2.5% CO₂ into water below soil in covered funnels increased the CO₂ gradient and increased nematode extraction, whereas bubbling air without CO₂ below soil purged CO₂ from the water and decreased nematode extraction. Manipulation of CO₂ within funnels usually increased extraction by only 30% and never by more than 3-fold. Controlling temperature gradients consistently increased extraction by 2-30-fold.     

Variability and possible adaptive significance of day-time vertical distribution ofLeptodora kindtii (Focke) (Cladocera) in a shallow eutrophic lake

The day-time vertical distribution of different size classes ofLeptodora kindtii in Tjeukemeer was studied during two contrasting years: 1978 and 1979. During the first year (1978) the predation pressure exerted by the planktivorous fish was rather high, whilst this was ca. 15 times lower during 1979. The diel vertical migration of different size classes ofLeptodora, was studied twice during 1979. Both studies support the predator avoidance hypothesis and also emphasize the idea that diel vertical migration is a dynamic rather than a fixed behaviour trait within a population.     

巨蝮蛇(Lachesis muta)毒出血毒素的纯化和性质研究

应用Sephadex G—75凝胶过滤、DEAE-Sephadex A-50离子交换层析和DEAE-3 SW Spherogel高压液相层析三步分离纯化程序,从巴西巨蝮蛇毒中获得二个具有蛋白水解酶活力的出血毒素Ⅳ—Ⅱ和Ⅳ—Ⅲ。它们在SDS凝胶电泳鉴定时显示出单一的蛋白带。IV—Ⅱ和Ⅳ—Ⅲ的分子量用SDS凝胶电泳测定分别为22,000和23,000,而等电点分别为6.50和6.12。Ⅳ—Ⅱ的最小出血剂量是25微克,Ⅳ—Ⅲ是0.5微克。当这两个出血毒素分别与纤维蛋白原保温时,都具有像胞浆素水解纤维蛋白原的作用,它们的分子中都含有金属Zn。     

Measurement of intra-embryonic pH during the early stages of development in the chick embryo

Summary Measurements have been made of the pH in the extracellular space, adjacent to the neural tube, in 73 isolated chick embryos in vitro at stages from 4–22 somites. A pH of 7.8–8.4 was observed in the segmented region, while caudally, in the segmental plate, the pH was consistently lower falling by as much as 0.5 pH units at the regressing primitive streak. Variations were noted in the pH of embryos of the same age but the regional variation in pH was a consistent finding in all of the embryos examined. The buffering capacity of the extracellular space was found to be 12.9 mequiv/pH unit/1 in the segmented region and 13.9 mequiv/pH unit/1 in the segmental plate. Thus it is unlikely that the regional variations in pH result from local variations in the buffering power of the extracellular space. Varying the K⁺, Cl^-, Mg²⁺ or HCO ₃ ^- ion concentrations in the bathing medium caused little change in the intra-embryonic pH, while reducing the concentrations of Na⁺ or Ca²⁺ caused a small acidification. This suggests that the ectoderm and endoderm form an effective barrier between the embryo and the external environment. Exposure of the embryo to KCN reduced the intra-embryonic pH suggesting that the alkaline environment is maintained by active processes.     

荔枝的光合特性

在低光强(0至0.15m mol m~(-2)s~(-1))下,荔枝叶子的光合速率随光入射量子通量的增高而增大。在光强0.7m mol m~(-2)s~(-1)时光合速率为1.76μmol m~(-2)s~(-1)。光合作用的光补偿点约为0.02 m mol m~(-2)s~(-1)光量子。荔技叶子具有低的气孔对水分传导率。气孔对水分传导率和蒸腾速率在低光强时随入射量子通量增高而增大:而细胞间CO_2浓度随光强增高而下降。在光强高于0.2m mol m~(-2) s~(-1)光量子时,细胞间CO_2浓度变化较少。在低光强时,叶子的水分利用效率(光合/蒸腾)随光强增高而增大。在光强高于0.2m mol m~(-2) s~(-1)光量子时,水分利用效率明显降低。荔枝叶子的最适光合作用叶温为22-26℃。可能表明在华南夏季中午的高温限制荔枝的田间光合作用。外界CO_2浓度增高相应增高细胞间CO_2浓度。当细胞间CO_2浓度约低于230μ1.1~(-1)时,光合速率随细胞间CO_2浓度增高而增大。在更高的细胞间CO_2浓度对,光合速率变化则较少。荔枝叶子光合速率对叶子/空气水蒸汽压陡度的变化响应不敏感。气孔对水分传导率和细胞间CO_2浓度随叶子/空气水蒸汽压陡度增大略有降低。