用废啤酒酵母制备碱不溶性葡聚糖的研究

研究了用碱法及酶－碱法从啤酒厂排弃的酵母泥中制备碱不溶性葡聚糖的工艺。对NaOH及蛋白酶用量的影响,NaOH作用时间、浓度、作用次数等因素的影响进行了较系统的探讨。先用蛋白酶处理酵母可减少NaOH用量从而减轻环境污染。对多糖产品进行了定性定量分析,得到的产品主要为β（1→3）-D-葡聚糖。     

富铬酵母的理化性质和氨基酸分析

用２００～３００ｎｍ的波长范围对富铬酵母及普通酵母的溶液进行紫外扫描,发现在λ_(２６０ｎｍ)处有一特征紫外吸收峰,富铬酵母细胞的铬含量与其吸收峰的光密度呈线性关系;在不同的温度和ｐＨ值条件下,通过紫外吸收峰的测定,富铬酵母溶液在酸性条件下稳定,在碱性条件下不稳定。溶液的λ_(２６０ｎｍ)紫外吸收峰随着温度的上升而升高。从氨基酸含量分析结果看,富铬酵母的谷氨酸、甘氨酸、组氨酸、丙氨酸和赖氨酸含量高于普通酵母,但其他氨基酸含量比普通酵母低。     

THE ORGANIC-INORGANIC RELATIONSHIP IN CALCIFIED MITOCHONDRIA

Experimentally induced calcification within mitochondria has been studied electron rnicroscopically. Cells investigated comprise hepatic cells damaged by CCl₄ intoxication, myocardial cells damaged by prolonged dihydrotachysterol (DHT) administration, and cells from skeletal muscle (gastrocnemius) damaged by DHT sensibilization and local injury. Cells from a human bowel carcinoma were studied too. Two types of intramitochondrial inorganic inclusion have been found. The first consists of clusters of apatite-like, needle-shaped crystals (crystalline aggregates), the second of clusters of very fine granules (granular aggregates). The former have been found mainly in mitochondria in apparently normal myocardial and muscular cells, the latter in mitochondria of degenerated hepatic, neoplastic, and myocardial cells. Crystalline aggregates are closely related to the membranes of cristae at first, but they later spread to occupy the whole mitochondrial matrix. Granular aggregates are initially found in the mitochondrial matrix near, but perhaps not touching, cristae; by growing they come into close contact with cristal membranes. Both types of aggregate show intrinsic electron opacity, which disappears after formic acid decalcification. Only the crystalline aggregates give an electron diffraction pattern of crystallinity. Uranium and lead staining of decalcified sections shows that both types of aggregate are intimately connected with an organic substrate. The substrate of crystalline aggregates consists of very thin, elongated structures shaped like the inorganic crystals. The substrate of granular aggregates consists of amorphous material gathered in clusters, with the same roundish shape and intercristal position as the inorganic granules. Both types of substrate are stained by phosphotungstic acid at low pH and by silver nitrate-methenamine after periodic acid oxidation. These results show that the organic content of the substrates includes glycoproteins; they have been confirmed by the periodic acid-Schiff (PAS) method under the optical microscope. These findings have been discussed in relation to the recent discovery of organic Ca²⁺-binding sites in mitochondria and to the general problems of soft tissue calcification.     

PHYSIOLOGICALLY INDUCED CHANGES IN ADRENOCORTICAL MITOCHONDRIA

1. Adrenocortical mitochondria contain filamentous or saccular internal membranes and are probably the sites of lipide elaboration or accumulation. They are numerous in the stimulated gland and scanty after hypophysectomy. There is evidence that they are expendable: light cells contain numbers of irregularly vacuolated and broken mitochondria with disorganized internal membranes. 2. Openings have been observed in some mitochondrial limiting membranes, particularly in the stimulated hamster and rat adrenal cortices, but to a lesser extent in the unstimulated glands. 3. Similarities between mitochondrial and Golgi membranes suggest a possible mode of mitochondrial formation. 4. These findings have been interrelated and discussed.     

VARIATIONS IN THE STRUCTURE OF MITOCHONDRIA

A characteristic internal structure, consisting of a double-layered outer wall enclosing a matrix-filled space through which pass double-layered membranous folds, would appear to comprise as satisfactory a definition of mitochondria for electron microscopy as their intravital affinity for Janus green affords for light microscopy. Relying for identification upon this characteristic internal structure, mitochondria appear to be pleomorphic structures which vary in size, shape, complexity, and density. They are labile also in that their number may increase or decrease under controlled conditions. The possibility therefore exists that these organelles are constantly being formed and destroyed, perhaps by their participation in metabolic processes. The problem of the origin of mitochondria is in an unsatisfactory state. New organelles unquestionably are formed in particular physiological states. The possibility that new bodies are produced by fission of ones already present does not seem adequate. On the other hand, the possible fabrication of new mitochondria out of intracellular membranes, although an attractive hypothesis, has not been adequately substantiated.     

RESPIRATION IN IMMATURE RAT BRAIN MITOCHONDRIA

—Respiration was studied polarographically in mitochondria isolated from immature rat cerebral hemispheres. Respiratory rates are compared as a function of age, substrate, and the requirement for a phosphate acceptor. 1. All respiratory rates are low in the first week of life. These rates increase during the first month and then decline to about the newborn rate by 5 weeks of age. 2. With the NAD-linked substrate pair, glutamate and malate, the changes with age are significant only for the rate of ADP-dependent respiration. With succinate as substrate, significant age-dependent changes in respiration occur only in ADP-independent respiration. 3. In mitochondria from animals less than five weeks of age, the ADP-dependent respiratory rate is significantly greater with the NAD-linked substrate pair than with succinate. In mitochondria from older animals, both ADP-dependent and ADP-independent rates are greater with succinate.     

FACTORS INFLUENCING RESPIRATORY CONTROL IN BRAIN MITOCHONDRIA

A simple technique was described for isolation of the mitochondrial fraction from central nervous tissue of the rat. The fraction so prepared satisfied structural and functional criteria of intactness and relative homogeneity. Oxidation of various substrates and the influences of inhibitors and experimental conditions were examined. The refractoriness of brain mitochondria to thyroxine was confirmed. Oxidation of glutamate was characterized by a very high degree of respiratory control. There was a pronounced Mg requirement by mitochondria in the aerobic active state, but not in the controlled state. Reverse acceptor control was manifest during succinate oxidation by Mg deficient mitochondria.     

GENESIS OF MITOCHONDRIA IN INSECT FAT BODY

Electron microscopy and stereological methods have been used to study the time course and mechanism of mitochondrial genesis in the adult fat body of Calpodes ethlius, (Lepidoptera, Hesperiidae). Most of the larval mitochondria are destroyed during a phase of autolysis shortly before pupation, so that pupal and early adult fat body cells have few mitochondria. The number of mitochondria per cell increases rapidly at the end of the 1st day after the adult emerges. Characteristic partitioned mitochondria appear during the period when the number is rapidly increasing. This evidence, coupled with the results of morphometric analyses of mitochondrial diameter, volume, and surface area, confirms the view that the genesis of adult mitochondria involves the growth and division of mitochondria surviving from the larva.     

外源性线粒体DNA在细胞内的重建(简报)

近年来发现人类多种神经肌肉疾病存在线粒体电子传递链(electron transport chain,ETC)缺陷。由于线粒体在遗传上受核基因和线粒体基因双重控制,给确定ETC缺陷的来源造成困难。转线粒体DNA技术是线粒体同无线粒体DNA的细胞(ρ°cells)融合,形成转线粒体DNA细胞系(mtDNA-transferred cell line,也称cytoplasmic hybrids,简称cybrids),使病人的线粒体DNA(mito-     

FORMATION OF AUXIN IN YEAST CULTURES

We have found far more auxin in the culture media of bakers'' yeast than was obtained by Kögl and Kostermans from the cells themselves. The production of auxin by yeast cells resembles the formation observed in other organisms such as Rhizopus and Rhizobium which also form auxins in their culture media. The auxin yield was found to increase with the concentration of sucrose and to decrease with the concentration of peptone. An inverse relation with the rate of cell multiplication was observed. Enlarged and elongated cells appeared only in those media which contained considerable amounts of auxin. The total auxin yield in the various cultures was found to be directly proportional, below pH 5, to the hydrogen ion concentration. Thus, it was proposed that certain growth conditions favor the breakage of the link between auxin and its protein carrier (Skoog and Thimann) 1940) and consequently accelerate the rate of excretion of auxin into the growth medium.     

FINE STRUCTURE IN FROZEN-ETCHED YEAST CELLS

The freeze-etching technique, which is a special kind of freeze-drying, allows electron microscopic investigation of cells and tissues in the frozen state. In regard to yeast cells (Saccharomyces cerevisiae) a freeze-fixation technique has been developed which does not kill the object. The electron micrographs therefore are considered to impart an image of high fidelity. The cutting of the frozen object, which actually consists of a fine splintering, produces not only cross-sectional views (cross-fractures) of the structures but also surface views of the membranes and organelles. Many surface structures are described which have not been shown by the usual sectioning techniques. The cytoplasmic membrane contains hexagonal arrangements of particles which are apparently involved in the production of the glucan fibrils of the cell wall. Alterations of the distribution of nuclear pores are shown in cells of different ages. Freeze-etching enables a clear distinction of endoplasmic reticulum and vacuoles in yeast cells. The membranes of the vesicular systems are covered by ribosomes arranged in circular patterns. The mitochondrial envelope shows small perforations which could allow the exchange of macromolecules. The storage granules consist of concentric layers of lipid, presumably phosphatide. A Golgi apparatus has been detected which may be involved in the storage of lipid. The structure of the unit membrane and the membrane structures of all organelles as revealed by chemical fixation are confirmed in principle. Glycogen agglomerations are identified in the ground plasm of older cells. Insight into artifacts introduced by common chemical fixation and embedding techniques is obtained and discussed.     

VARIABILITY IN THE YEAST HANSENULA HOLSTII

In the heterothallic yeast Hansenula holstii morphological variants consisting of a mother cell, stalk, and terminal cell are formed during vegetative growth. Tetrad distribution ratios of clones derived from mother and terminal cells differ. Preceding stalk formation endospore-like structures form in many cells. A causal relationship may exist between formation of the modified nuclei and change in the segregational patterns in the variants.     

MUTATIONAL MELTDOWN IN LABORATORY YEAST POPULATIONS

Abstract.— In small or repeatedly bottlenecked populations, mutations are expected to accumulate by genetic drift, causing fitness declines. In mutational meltdown models, such fitness declines further reduce population size, thus accelerating additional mutation accumulation and leading to extinction. Because the rate of mutation accumulation is determined partly by the mutation rate, the risk and rate of meltdown are predicted to increase with increasing mutation rate. We established 12 replicate populations of Saccharomyces cerevisiae from each of two isogenic strains whose genomewide mutation rates differ by approximately two orders of magnitude. Each population was transferred daily by a fixed dilution that resulted in an effective population size near 250. Fitness declines that reduce growth rates were expected to reduce the numbers of cells transferred after dilution, thus reducing population size and leading to mutational meltdown. Through 175 daily transfers and approximately 2900 generations, two extinctions occurred, both in populations with elevated mutation rates. For one of these populations there is direct evidence that extinction resulted from mutational meltdown: Extinction immediately followed a major fitness decline, and it recurred consistently in replicate populations reestablished from a sample frozen after this fitness decline, but not in populations founded from a predecline sample. Wild‐type populations showed no trend to decrease in size and, on average, they increased in fitness.     

MITOSIS IN THE YEAST LIPOMYCES LIPOFER

A study of mitosis in Lipomyces has been carried out because preliminary observations by Ganesan and Roberts, 1959 (9), had indicated that the nucleus of this yeast might be unusually favourable for morphological observations. This impression has proved correct. The chromosomes of Lipomyces are visible as separate, countable bodies for the greater part of mitosis. The pattern of mitosis differs from the common one in that in Lipomyces the proper distribution of sister chromosomes is accomplished without the help of a spindle apparatus. At the end of prophase sister chromosomes are found in pairs which align themselves parallel to one another to form a palisade or stack whose long axis coincides with the axis of the impending division. At anaphase-telophase the stack of paired chromosomes fuses into a seemingly homogeneous cord which divides by constriction.