THE SIZE OF PORES IN COLLODION MEMBRANES

By the application of Poiseuille''s law to the rate of flow of water through collodion membranes, it is calculated that the membranes used had pore radii of the order of 0.3 to 2 x 10^–6 cm. On the same basis the number of pores per sq. cm. appears to vary from 270 x 10¹⁰ to 7 x 10¹⁰, decreasing with increase in pore size. Reasons are given for preferring these figures for the radii to figures, 100 times as large, which were calculated by others. Microscopic examination of the membranes, with dark-field illumination, indicates that they are made up of solid granules or filaments of collodion much less than 1 x 10^–4 cm. in thickness.     

THE SIZE OF THE CELLULOSE MICROFIBRIL

Recently the lateral width of the cellulose microfibril has been estimated as 30 A rather than about 150 to 200 A, by extrapolation of data from model shadowing experiments. The difference was attributed to a layer of metal deposited during shadowing. However, direct photographs of the same microfibrils parallel and perpendicular to the direction of shadowing, of unshadowed portions of microfibrils compared with shadowed portions of the same microfibrils, of silver-stained unshadowed microfibrils, and of unshadowed, unstained segments of microfibrils give no evidence of a layer of metal of this thickness in material shadowed under normal conditions. Furthermore, the evidence for microfibril strands of about 35 A in width from negative-staining experiments is subject to a bias from the form of the filaments and from variable positive adsorption of phosphotungstic acid by cellulose. Consequently, the conclusion that the true lateral width of native cellulose microfibrils is about one-fifth of the presently accepted value is not yet justified by unequivocal direct experimental evidence.     

ISOLATION AND CHARACTERIZATION OF MYELIN-RELATED MEMBRANES

Abstract— Myelin related membrane fractions from rat brain and spinal cord were isolated from material normally discarded during standard myelin isolation procedures. A fraction which floated on 0.32 M-sucrose (F) and the material released after subjecting the myelin fraction to osmotic shock at two stages in the purification (W₁ and W₂) were characterized. These fractions were subjected to subfractionation on three step discontinuous sucrose gradients. Morphologically, the heavier subfrac-tions of W₁ and W₂ were shown to consist mainly of single membranes and vesicles. Sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis showed that, relative to myelin, proteolipid and basic protein were reduced in all subfractions, while the high molecular weight proteins were increased. The specific activity of 2′,3′-cyclic nucleotide 3′-phosphohydrolase (CNP) was up to 2-fold higher than that of myelin in the heavier subfractions of W₁ and W₂. The major myelin-associated glycoprotein was also increased in these subfractions as determined by periodic acid-Schiff staining. Differential centrifugation of the initial tissue homogenate to remove microsomes prior to myelin isolation gave rise to W₁ and W₂ subfractions with a CNP specific activity 3–4 times that of myelin. The high molecular weight proteins and glycoproteins were enriched in these microsome-depleted subfractions, but were qualitatively similar to those of myelin. Some of the membranes in these fractions may be derived from the continuum between the plasma membrane of the oligodendrocyte and compact myelin. Fraction F consisted of small membrane fragments and many vesicles, and was particularly deficient in proteolipid. The specific activity of CNP in fraction F was about the same as myelin, while the major myelin associated glycoprotein could not be detected. Fraction F from normal CNS tissue appears to be similar to the floating fractions previously isolated in larger amounts from pathological brain undergoing edematous demyelination.     

ZONAL CENTRIFUGATION OF NEURONAL PERIKARYA AND ISOLATION OF NEURONAL MEMBRANES RICH IN ACETYLCHOLINESTERASE

Abstract— A method is presented that allows the isolation of neuronal perikarya of high purity and in good yield from rat brain. To this procedure is coupled a second isolation step which affords neuronal membranes in preparative quantities. The arrangement of the two isolation steps in tandem ensures that the final preparation has a high degree of purity with respect to both its neuronal origin and its membrane content. The membranes so obtained do not constitute plasma membranes but rather represent intracellular structures that are predominantly derived from endoplasmic reticulum and contain mitochondrial elements as well. During the process of membrane purification AChE is enriched four-fold while cholinesterase is concurrently eliminated. The present method supplements the procedure reported by M organ , W olfe , M andel and G ombos (1971) for the isolation of synaptosomal plasma membranes. It may also open access to a useful source of brain AChE.     

AQUEOUS POLYMER TWO-PHASE SYSTEMS AND THEIR USE IN FRAGMENTATION AND SEPARATION OF BIOLOGICAL MEMBRANES FOR THE PURPOSE OF MAPPING THE MEMBRANE STRUCTURE

When solutions of two different polymers are mixed, phase separation often occurs even at low concentrations of polymers. One polymer usually collects in one phase and the other polymer in the other phase. When water is used as solvent, two aqueous, immiscible, phases are obtained. The same holds for aqueous mixtures of a salt and a polymer. Such aqueous two-phase systems (ATPS) are very useful for separation of high-molecular-weight biomolecules such as proteins and nucleic acids and also for cells, cell organelles, and membrane vesicles. The phase systems can be made highly selective and they are also mild toward biomolecules and cell particles. In this review we describe how ATPS can be used for fragmentation and separation analyses of biological membranes and how this can be used for mapping of the photosynthetic membrane, the thylakoid, of green leaves.     

INCREASE IN SIZE AND CELL NUMBER OF LATERAL ROOT PRIMORDIA IN THE PRIMARY OF INTACT PLANTS AND IN EXCISED ROOTS OF PISUM SATIVUM AND VICIA FABA

Increase in cell number, and in anlage volume and length have been investigated during the development of lateral root primordia in roots of intact plants of Pisum sativum and Vicia faba and in excised roots of both species cultured in White's medium supplemented with 2% sucrose. With the exception of primordia in excised roots of Vicia, the general equation which best described increase in each aspect of primoridium growth measured against time was that for exponential growth. When the times necessary for cell number and primordium volume and length to double were determined at intervals over the period of development studied, however, they were found to vary. Similarly, estimates of the size of the proliferative fraction of cells at different times during anlage development indicated that this index of meristematic activity also fluctuated over the developmental period investigated, i.e., increase in cell number and in primordium volume and length do not occur in a truly exponential fashion as the primordia increase in size and cell number. One difference between anlage development in the roots of intact plants and in those grown in culture was that whereas the former primordia completed their development and emerged as lateral roots over the period of the investigation, the latter did not. Moreover, cell doubling time and anlage volume and length doubling times were longer, and the proliferation fraction of cells lower, over the whole period of, and at intervals during, primordium development in the excised roots compared with the results obtained for the roots of the corresponding intact plants.     

ISOLATION AND CHARACTERIZATION OF LUMINAL MEMBRANES FROM URINARY BLADDER

A method is reported for the isolation of a highly purified fraction of urinary bladder membranes containing hexagonal plaques. The method uses zonal centrifugation as the final step of fractionation. The purified fraction was characterized by its electron microscopic morphology, by its enzymatic profile, by quantitative and qualitative analysis of lipids and by the protein pattern obtained by electrophoresis in polyacrylamide sodium dodecyl sulfate gels. The fraction contains 65% lipids and 35% proteins. The major protein component has a molecular weight of 27,000 daltons. Phospholipids are more than the 54% of the total lipid weight. Phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol are the major phospholipids with 50%, 30%, and 7% of the total lipid phosphorus, respectively. The glycolipid fraction is 10% of the total lipid weight and is formed by only two components, both sulfatides. Total cholesterol makes up 36% of the total neutral lipid fraction of which cholesterol esters constitute 6%. Glycoproteins are also found to be present in the fraction.     

THE USE OF MICROBIAL MEMBRANES TO ACHIEVE ANAEROBIOSIS

Several years ago, it was observed that sterile microbial membrane preparations stimulated recovery of certain radiation-injured bacteria. Later it was noted that these same preparations reduce dissolved oxygen to water in a variety of environments, including bacteriological media. This reduction of oxygen is an enzymatic process and is influenced by parameters such as temperature, pH, and the availability of specific oxidizable substrates. Oxygenreducing membrane preparations can be made from several different bacterial species. When added to liquid or solid bacteriological media, membrane preparations rapidly produce and maintain anaerobic conditions favorable for the growth of a wide variety of oxygen-sensitive microorganisms. When used with a specifically designed disposable dish, membrane preparations allow the development of colonies of many anaerobic microorganisms on the surface of agar without the use of anaerobic hoods or other devices. In addition to providing conditions suitable for the growth of anaerobes, membrane preparations stimulate recovery of heat and cold injured bacteria of several different genera including facultative organisms. These results are reminiscent of the early observations regarding the recovery of radiation-injured bacteria. In addition to their usefulness in microbiology, oxygen-reducing membrane preparations have the potential for protecting a wide variety of oxygen-sensitive organic compounds.     

THE USE OF MULTIPLE REGRESSION ANALYSIS FOR ESTIMATING THE ACTION PATTERN OF CELLULASE FRACTIONS IN HYDROLYSIS OF CELLULOSE

A comprehensive regression model was developed for estimating theaction pattern of three cellulase fractions (β-1,4-glucan cellobiohydrolase,endo-glucanase and cellobiase)in hydrolysis of cellulose.The effect of stru-cture feature of cellulose on hydrolysis can also be evaluated by using thismodel.The results suggested that this technique was suitable for estimatingthe action pattern of cellulase fractions in cellulose hydrolysis,especiallyin quantitative eluciation of the effect of each fraction,alone or in combin-ation of which.     

酶抑制动力学模型判断中的统计分析

文章用数理统计的方法导出了酶抑制动力学研究中双倒数作图法的统计模型,克服了作图法中主观因素的干扰,建立了判断竞争抑制,非竞争抑制,反竞争抑制,线性混合抑制的统计分析方法。     

CHITIN AND CELLULOSE IN THE CELL WALLS OF RHIZIDIOMYCES SP

Fuller , Melvin S. (Brown U. Providence, R. I.), and Isaac Barshad . Chitin and cellulose in the cell walls of Rhizidiomyces sp. Amer. Jour. Bot. 47(2): 105-109. Illus. 1960.–Chemically isolated cell wall preparations of the aquatic Phycomycete, Rhizidiomyces sp., were analyzed by means of X-rays. The resulting diffraction patterns had maxima corresponding with known values for chitin and mercerized cellulose. The findings in this study are discussed with respect to Von Wettstein's hypothesis that the aquatic Phycomycetes can be separated into groups on the basis of whether their cell walls contain chitin or cellulose.