植物离体茎段嫁接

植物体茎段嫁接系统是在无菌条件下将茎切段嫁接后放入培养基中、使接穗和砧木分别与含不同成分的培养基接触,再署光下培养的一个模拟植物正常生理过程、环境条件可控的实验系统,离体茎段嫁接体的发育与整体类拟,包括接穗与砧木粘连、愈伤组织产生、次生甩间连丝形成和维管束分化等几个步骤,发育进程受植物激素如生长素和细胞分裂素调节。该系统的建立为阐明嫁接体发机理及嫁接亲和性机制提供了重要的依据。     

Probing the Interaction Forces of Prostate Cancer Cells with Collagen I and Bone Marrow Derived Stem Cells on the Single Cell Level

Adhesion of metastasizing prostate carcinoma cells was quantified for two carcinoma model cell lines LNCaP (lymph node-specific) and PC3 (bone marrow-specific). By time-lapse microscopy and force spectroscopy we found PC3 cells to preferentially adhere to bone marrow-derived mesenchymal stem cells (SCP1 cell line). Using atomic force microscopy (AFM) based force spectroscopy, the mechanical pattern of the adhesion to SCP1 cells was characterized for both prostate cancer cell lines and compared to a substrate consisting of pure collagen type I. PC3 cells dissipated more energy (27.6 aJ) during the forced de-adhesion AFM experiments and showed significantly more adhesive and stronger bonds compared to LNCaP cells (20.1 aJ). The characteristic signatures of the detachment force traces revealed that, in contrast to the LNCaP cells, PC3 cells seem to utilize their filopodia in addition to establish adhesive bonds. Taken together, our study clearly demonstrates that PC3 cells have a superior adhesive affinity to bone marrow mesenchymal stem cells, compared to LNCaP. Semi-quantitative PCR on both prostate carcinoma cell lines revealed the expression of two Col-I binding integrin receptors, α1β1 and α2β1 in PC3 cells, suggesting their possible involvement in the specific interaction to the substrates. Further understanding of the exact mechanisms behind this phenomenon might lead to optimized therapeutic applications targeting the metastatic behavior of certain prostate cancer cells towards bone tissue.     

Adhesive forces in embryonic stem cell cultures

Most cell culture systems grow and spread as contact-inhibited monolayers on flat culture dishes, but the embryonic stem cell (ESC) is one of the cell phenotypes that prefer to self-organize as tightly packed three-dimensional (3D) colonies. ESC also readily form 3D cell aggregates, called embryoid bodies (EB) that partially mimic the spatial and temporal processes of the developing embryo. Here, the rationale for ESC aggregation, rather than “spreading” on gelatin-coated or mouse embryonic fibroblast (MEF)-coated dishes, is examined through the quantification of the expression levels of adhesion molecules on ESC and the calculation of the adhesive forces on ESC. Modeling each ESC as a dodecahedron, the adhesive force for each ESC-ESC binding was found to be 9.1 × 10⁵ pN, whereas, the adhesive force for ESC-MEF binding was found to be an order of magnitude smaller at 7.9 × 10⁴ pN. We also show that E-cadherin is the dominating molecule in the ESC-ESC adhesion and blocking E-cadherin leads to a significant reduction in colony formation. Here, we mathematically describe the preference for ESC to self-assemble into ESC-ESC aggregates and 3D colonies, rather than to bind and spread on gelatin or MEF-coated dishes, and have shown that these interactions are predominantly due to E-cadherin expression on ESC.Key words: embryonic stem cells, stem cell morphology, E-cadherin, beta-1 integrin, cell adhesive forces, quantitative flow cytometry     

Histopathological and biochemical aspects of grafted and non-grafted cucumber infected with stem rot caused by Fusarium spp.

Cucumber grafting has been used in Egypt recently to induce soil diseases tolerance. The impact of various grafting techniques on the vulnerability of grafted cucumber seedlings to Fusarium which stimulates the stem rot was investigated. Consequently, the anatomical and physiological studies were carried out on the diseased and healthy grafted cucumber seedlings, comparing with the non-grafted ones. Fusarium equiseti (MW216971.1) caused a severe stem rot of the grafted seedling through affecting the connection area of the different grafting methods, leading to complete seedling death. The hole insertion grafting method significantly exhibited the highest diseases incidence (100%), and mean disease severity index (5) when inoculated with F. equiseti. The pathogen remarkably affected the graft union area causing tissue discoloration and decay. The levels of antioxidant enzymes and total phenols were significantly enhanced in the diseased grafted and self-rooted cucumber. However, the diseased grafted cucumber recorded significantly the highest values of the antioxidant enzymes activities and total phenolic content when compared with the self-rooted ones. The results of SDS-PAGE profile revealed variations in the leaves protein profile of the grafted and self- rooted seedlings in response to Fusarium infection. Taken together, grafting cucumber onto a resistant rootstock using the splice technique can alleviate the stem rot severity caused by Fusarium spp. by enhancing the histological, physiological and molecular defense response of the grafted seedling.     

Guidance of Mesenchymal Stem Cells on Fibronectin Structured Hydrogel Films

Designing of implant surfaces using a suitable ligand for cell adhesion to stimulate specific biological responses of stem cells will boost the application of regenerative implants. For example, materials that facilitate rapid and guided migration of stem cells would promote tissue regeneration. When seeded on fibronectin (FN) that was homogeneously immmobilized to NCO-sP(EO-stat-PO), which otherwise prevents protein binding and cell adhesion, human mesenchymal stem cells (MSC) revealed a faster migration, increased spreading and a more rapid organization of different cellular components for cell adhesion on fibronectin than on a glass surface. To further explore, how a structural organization of FN controls the behavior of MSC, adhesive lines of FN with varying width between 10 µm and 80 µm and spacings between 5 µm and 20 µm that did not allow cell adhesion were generated. In dependance on both line width and gaps, cells formed adjacent cell contacts, were individually organized in lines, or bridged the lines. With decreasing sizes of FN lines, speed and directionality of cell migration increased, which correlated with organization of the actin cytoskeleton, size and shape of the nuclei as well as of focal adhesions. Together, defined FN lines and gaps enabled a fine tuning of the structural organization of cellular components and migration. Microstructured adhesive substrates can mimic the extracellular matrix in vivo and stimulate cellular mechanisms which play a role in tissue regeneration.     

Developmental and genotypic differences in the response of pea stem segments to auxin

The objective of this investigation was to examine the response to exogenous auxin (indole-3-acetic acid; IAA)of stem segments at two developmental stages. The standard auxin response of excised stem segments and intact plants consists of an initial growth response and a prolonged growth response. We found that this biphasic response does not occur in internodes at very early stages. Stem segments of light grown pea of various genotypes were cut when the fourth internode was at 6–13% of full expansion (early-expansion) or at 18–25% of full expansion (mid-expansion). Length measurements of excised segments were made after 48 hours of incubation on buffer with or without auxin. An angular position transducer linked to a computerized data collection system provided high-resolution measurement of growth of stacks of segments incubated in buffer over 20 hours. Early-expansion segments of all genotypes deviated from the standard auxin response, while mid-expansion segments responded in a manner consistent with previous reports. Early-expansion segments of tall, light-grown plants were unique in showing an auxin-induced inhibition of growth. The auxin-induced inhibition correlated with high endogenous auxin content, as determined by HPLC and GC/MS, across genotypes and between early-expansion and mid-expansion segments of tall plants. Measurement of ethylene evolved from stem segments in response to auxin, and treatment of segments with the ethylene action inhibitor, norbornadiene, showed the inhibition to be mediated in part by heightened ethylene sensitivity. Growth of early-expansion segments of dwarf and severe dwarf plants was stimulated by exogenous auxin, but the growth rate increase was delayed compared to that in mid-expansion segments. This is the first time that such a growth response, termed the delayed growth response has been emonstrated. It is concluded that developmental stage and endogenous hormone content affect tissue response to exogenous auxin.     

Nanoscale Imaging Reveals a Tetraspanin-CD9 Coordinated Elevation of Endothelial ICAM-1 Clusters

Endothelial barriers have a central role in inflammation as they allow or deny the passage of leukocytes from the vasculature into the tissue. To bind leukocytes, endothelial cells form adhesive clusters containing tetraspanins and ICAM-1, so-called endothelial adhesive platforms (EAPs). Upon leukocyte binding, EAPs evolve into docking structures that emanate from the endothelial surface while engulfing the leukocyte. Here, we show that TNF-α is sufficient to induce apical protrusions in the absence of leukocytes. Using advanced quantitation of atomic force microscopy (AFM) recordings, we found these structures to protrude by 160 ± 80 nm above endothelial surface level. Confocal immunofluorescence microscopy proved them positive for ICAM-1, JAM-A, tetraspanin CD9 and f-actin. Microvilli formation was inhibited in the absence of CD9. Our findings indicate that stimulation with TNF-α induces nanoscale changes in endothelial surface architecture and that—via a tetraspanin CD9 depending mechanism—the EAPs rise above the surface to facilitate leukocyte capture.     

Uncoiling mechanics of Escherichia coli type I fimbriae are optimized for catch bonds

We determined whether the molecular structures through which force is applied to receptor–ligand pairs are tuned to optimize cell adhesion under flow. The adhesive tethers of our model system, Escherichia coli, are type I fimbriae, which are anchored to the outer membrane of most E. coli strains. They consist of a fimbrial rod (0.3–1.5 μm in length) built from a helically coiled structural subunit, FimA, and an adhesive subunit, FimH, incorporated at the fimbrial tip. Previously reported data suggest that FimH binds to mannosylated ligands on the surfaces of host cells via catch bonds that are enhanced by the shear-originated tensile force. To understand whether the mechanical properties of the fimbrial rod regulate the stability of the FimH–mannose bond, we pulled the fimbriae via a mannosylated tip of an atomic force microscope. Individual fimbriae rapidly elongate for up to 10 μm at forces above 60 pN and rapidly contract again at forces below 25 pN. At intermediate forces, fimbriae change length more slowly, and discrete 5.0 ± 0.3–nm changes in length can be observed, consistent with uncoiling and coiling of the helical quaternary structure of one FimA subunit at a time. The force range at which fimbriae are relatively stable in length is the same as the optimal force range at which FimH–mannose bonds are longest lived. Higher or lower forces, which cause shorter bond lifetimes, cause rapid length changes in the fimbria that help maintain force at the optimal range for sustaining the FimH–mannose interaction. The modulation of force and the rate at which it is transmitted from the bacterial cell to the adhesive catch bond present a novel physiological role for the fimbrial rod in bacterial host cell adhesion. This suggests that the mechanical properties of the fimbrial shaft have codeveloped to optimize the stability of the terminal adhesive under flow.     

Geckos as Springs: Mechanics Explain Across-Species Scaling of Adhesion

One of the central controversies regarding the evolution of adhesion concerns how adhesive force scales as animals change in size, either among or within species. A widely held view is that as animals become larger, the primary mechanism that enables them to climb is increasing pad area. However, prior studies show that much of the variation in maximum adhesive force remains unexplained, even when area is accounted for. We tested the hypothesis that maximum adhesive force among pad-bearing gecko species is not solely dictated by toepad area, but also depends on the ratio of toepad area to gecko adhesive system compliance in the loading direction, where compliance (C) is the change in extension (Δ) relative to a change in force (F) while loading a gecko’s adhesive system (C = dΔ/dF). Geckos are well-known for their ability to climb on a range of vertical and overhanging surfaces, and range in mass from several grams to over 300 grams, yet little is understood of the factors that enable adhesion to scale with body size. We examined the maximum adhesive force of six gecko species that vary in body size (~2–100 g). We also examined changes between juveniles and adults within a single species (Phelsuma grandis). We found that maximum adhesive force and toepad area increased with increasing gecko size, and that as gecko species become larger, their adhesive systems become significantly less compliant. Additionally, our hypothesis was supported, as the best predictor of maximum adhesive force was not toepad area or compliance alone, but the ratio of toepad area to compliance. We verified this result using a synthetic “model gecko” system comprised of synthetic adhesive pads attached to a glass substrate and a synthetic tendon (mechanical spring) of finite stiffness. Our data indicate that increases in toepad area as geckos become larger cannot fully account for increased adhesive abilities, and decreased compliance must be included to explain the scaling of adhesion in animals with dry adhesion systems.     

Auxin Stimulation of Cambial Activity in Pinus silvestris II. Dependence upon Basipetal Transport

Natural auxin content has been determined in the cambial region of large Pinus silvestris L. trees at various dates during the year. The tissue was collected from the stem of intact or ring-barked trees and from stumps remaining after the trees were cut down at breast height in early summer or late autumn. No seasonal decrease of concentration of the extractable auxin in the cambial region could be detected. Decapitation or ring-barking produced severe reduction in auxin content and arrested cambial division. In the next season the auxin level and the cambial activity remained completely depressed. It is concluded that without tissue continuity in the region external to xylem and without basipetal supply of substances, no mechanism operated by roots or remaining stem tissue near the tree base can ensure a high level of auxin in the cambial region or activate and maintain the cambial division. The activity of extracted pine auxin was found not to be identical with the stimulatory potential of authentic IAA determined by standard bioassays. The possibility of interaction with other extracted substances is discussed.     

Protrusion Fluctuations Direct Cell Motion

Many physiological phenomena involve directional cell migration. It is usually attributed to chemical gradients in vivo. Recently, other cues have been shown to guide cells in vitro, including stiffness/adhesion gradients or micropatterned adhesive motifs. However, the cellular mechanism leading to these biased migrations remains unknown, and, often, even the direction of motion is unpredictable. In this study, we show the key role of fluctuating protrusions on ratchet-like structures in driving NIH3T3 cell migration. We identified the concept of efficient protrusion and an associated direction index. Our analysis of the protrusion statistics facilitated the quantitative prediction of cell trajectories in all investigated conditions. We varied the external cues by changing the adhesive patterns. We also modified the internal cues using drug treatments, which modified the protrusion activity. Stochasticity affects the short- and long-term steps. We developed a theoretical model showing that an asymmetry in the protrusion fluctuations is sufficient for predicting all measures associated with the long-term motion, which can be described as a biased persistent random walk.     

Auxin redistribution and shifts in PIN gene expression during Arabidopsis grafting

Auxin is important in the development of plant vascular tissues. Reconnection of vascular bundles between scion and stock is a primary aim of grafting, and polar auxin transport greatly affects the formation of a continuous vascular model. The role of auxin in the process of graft-union development was studied by grafting the seedlings of Arabidopsis thaliana (L.) Heynh. DR5:GUS marker plants, which exert the auxinspecific responses. Auxin induced the DR5:GUS expression in the vascular bundles around graft surface and stimulated the formation of multiple vascular bundle reconnections on the third day after grafting (DAG). DR5:GUS expression was delayed for one day in both scion and stock and dramatically declined by the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). Vascular bundle reconnection was observed only on the 4th DAG. These results suggest that auxin stimulates the reconnection of the vascular bundles, whereas NPA inhibits it. We studied the role of PIN proteins in graft development by grafting seedlings of PIN:GUS plants. PIN had different expression patterns in the graft process. Expression levels of PIN genes were analyzed by real-time PCR. All PIN genes had the higher expression level at the third DAG. We conclude that auxin stimulates the development of graft unions, and the patterns of expressions of PIN family genes can affect the development of graft-union by controlling the auxin flow.     

N-cadherin expression level as a critical indicator of invasion in non-epithelial tumors

Cancer cell dissemination away from the primary tumor and their ability to form metastases remain the major causes of death from cancer. Understanding the molecular mechanisms triggering this event could lead to the design of new cancer treatments. The establishment and the maintenance of tissue architecture depend on the coordination of cell behavior within this tissue. Cell-cell interactions must form adhesive structures between neighboring cells while remaining highly dynamic to allow and control tissue renewal or remodeling. Among intercellular junctions, cadherin-based adherens junctions mediate strong physical interactions and transmit information from the cell microenvironment to the cytoplasm. Disruption of these cell-cell contacts perturbs the polarity of epithelial tissues leading to their disorganization and ultimately to aggressive carcinomas. In non-epithelial tissues, the role of cadherins in the development of cancer is still debated. We recently found that downregulation of N-cadherin in malignant glioma—the most frequent primary brain tumor—results in cell polarization defects leading to abnormal motile behavior with increased cell speed and decreased persistence in directionality. Re-expression of N-cadherin in glioma cells restores cell polarity and limits glioma cell migration, providing a potential therapeutic tool for diffuse glioma.     

Passively stuck: death does not affect gecko adhesion strength

Many geckos use adhesive toe pads on the bottom of their digits to attach to surfaces with remarkable strength. Although gecko adhesion has been studied for hundreds of years, gaps exist in our understanding at the whole-animal level. It remains unclear whether the strength and maintenance of adhesion are determined by the animal or are passively intrinsic to the system. Here we show, for the first time, that strong adhesion is produced passively at the whole-animal level. Experiments on both live and recently euthanized tokay geckos (Gekko gecko) revealed that death does not affect the dynamic adhesive force or motion of a gecko foot when pulled along a vertical surface. Using a novel device that applied repeatable and steady-increasing pulling forces to the foot in shear, we found that the adhesive force was similarly high and variable when the animal was alive (mean ± s.d. = 5.4 ± 1.7 N) and within 30 min after death (5.4 ± 2.1 N). However, kinematic analyses showed that live geckos are able to control the degree of toe pad engagement and can rapidly stop strong adhesion by hyperextending the toes. This study offers the first assessment of whole-animal adhesive force under extremely controlled conditions. Our findings reveal that dead geckos maintain the ability to adhere with the same force as living animals, disproving that strong adhesion requires active control.     

Selectin- and integrin-mediated T-lymphocyte rolling and arrest on TNF-alpha-activated endothelium: augmentation by erythrocytes.

The adhesive and hemodynamic forces that lead to lymphocyte rolling and arrest on activated endothelium and the biophysical role of various adhesion molecules and blood elements in this process are poorly understood. By quantifying their behaviour both in vivo and in vitro, we show here that erythrocytes facilitate selectin- and integrin-mediated rolling and binding of T-lymphocytes on tumor necrosis factor alpha-activated endothelium. The relative contribution of selectins and integrins to this process can be distinguished by using a simple mathematical expression of lymphocyte capture within the range of physiological shear stress. The need for selectin participation in lymphocyte capture increases with shear stress (> 1 dyn/cm2), and both beta 1 and beta 2 integrins act in synergy to produce adhesive drag on captured cells. These findings are potentially useful in developing strategies for intervening with T-cells in a variety of normal and pathological responses as well as for the delivery of genetically modified T-cells to their targets in vivo.     

肝细胞生长因子对人羊水干细胞迁移和黏附能力的影响

目的分离培养及鉴定羊水干细胞（hAFSC）,并研究肝细胞生长因子（HGF）对羊水干细胞迁移、黏附能力的影响。方法使用细胞贴壁法分离培养羊水干细胞,细胞免疫荧光及westernblot鉴定羊水干细胞,Transwell小室分析HGF对羊水干细胞迁移的作用。明胶贴壁法分析HGF对羊水干细胞黏附能力的作用。两组之间数据的比较采用独立样本t检验。结果分离的羊水干细胞均表达特异性标记物Oct-4、c-kit、SSEA-4、CD105。HGF在体外对hAFSC的迁移有趋化作用,对照组和HGF组每个视野的迁移细胞数分别为38±2.5和80±3.2。对黏附能力有促进作用,对照组和HGF组每个视野的黏附细胞数分别为19±1.5和50±2.7,差异均有统计学意义（P〈0.01）。结论 HGF可趋化羊水干细胞的迁移,增强羊水干细胞的黏附能力。     

What drives interspecies graft union success? Exploring the role of phylogenetic relatedness and stem anatomy

The underlying mechanisms that determine whether two species can form a successful graft union (graft compatibility) remain obscure. Two prominent hypotheses are (1) the more closely related species are, the higher the graft success and (2) the vascular anatomy at the graft junction influences graft success. In this paper these two hypotheses are examined in a systematic way using graft combinations selected from a range of (a) phylogenetically close and more distant legume species, (b) species displaying different germination patterns and (c) scions and rootstocks possessing contrasting stem tissues and vascular patterns. Relatedness of species was not a good predictor of graft compatibility, as vascular reconnection can occur between distantly related species and can fail to occur in some more closely related species. Similarly, neither the stem tissues present at the graft junction nor the vascular anatomy correlated with the success of vascular reconnection. Relatedness and stem anatomy therefore do not appear to be the determining factors in successful vascular reconnection after grafting in legumes. These results are discussed in conjunction with other hypotheses such as the role of auxin.     

Modulation of spreading, proliferation, and differentiation of human mesenchymal stem cells on gelatin-immobilized poly(L-lactide-co--caprolactone) substrates

Controlled adhesion and continuous growth of human mesenchymal stem cells (hMSCs) are essential for scaffold-based delivery of hMSCs in tissue engineering applications. The main goal of this study is to develop biofunctionalized synthetic substrates to actively control adhesion, spreading, and proliferation of hMSCs. gamma-Ray irradiation was employed to graft acrylic acid (AAc) to biodegeradable poly(L-lactide-co--caprolactone) (PLCL) films. Gelatin, a natural polymer, was then immobilized on the AAc grafted PLCL film (AAc-PLCL) to induce biomimetic interactions with the cells. The graft yield of AAc increased as the irradiation dose and AAc concentration increased, and the presence of gelatin (gelatin-AAc-PLCL) following immobilization was confirmed using ESCA. To investigate cell responses, hMSCs isolated from a human mandible were cultured on the various substrates and their adhesion, spreading, and proliferation were examined. After three days of culture, the DNA concentration from the cells cultured on gelatin-AAc-PLCL film was 2.9-fold greater than that on the PLCL film. Immunofluorescent staining of hMSCs cultured on the gelatin-AAc-PLCL films demonstrated homogeneous localization of F-Actin and vinculin in their cytoplasm, while mature adhesive structure was not observed from the cells cultured on other substrates. Furthermore, the ratio of projected area of adherent single cells on gelatin-AAc-PLCL films was significantly larger (116.80 +/- 12.78%) than that on the PLCL films (30.11 +/- 5.07%). Our results suggest that gelatin-immobilized PLCL substrates may be potentially used in tissue engineering, particularly as a stem cell delivery carrier for the regeneration of target tissue.     

The role of cellulase in hormonal regulation of shoot morphogenesis in tobacco callus

A polyclonal antibody raised against cellulase (EC 3.2.1.4.) from callus ofNicotiana tabacum L. cv. Petit Havana SR1 reduced cellulase activity and induced shoot formation in tobacco callus in the presence of callus maintaining concentrations of auxin and cytokinin. Shoot induction as well as reduction of the cellulase activity was also obtained by withdrawing auxin from the callus medium. The effect of the two hormones on cellulase activity in the tobacco tissue was examined by varying the concentration of one of the hormones -naphthylacetic acid (NAA) or benzylaminopurine (BAP) at a time while the other was kept at a level sufficient for either callus growth or shoot induction. While NAA stimulated the enzyme activity increasingly with concentration in the range 5 × 10^–7 M to 5 × 10^–5 M at both levels of BAP, BAP only stimulated the cellulase activity at an optimum concentration of 5 × 10^–6 M when NAA was present at a level sufficient to induce callus growth. The results point to a pivotal role of the downward regulation of cellulase in the initiation of shoot induction. A series of events leading to oriented cell divisions as a result of the lowered cellulase level during the initial phase of the morphogenetic process is discussed.Abbreviations Ab Purified cellulase antibody - BAP benzylaminopurine - MS Murashige and Skoog medium - NAA -naphthylacetic acid - PS Purified preimmune serum We thank Mr. Poul Fabech for constructing the automatic viscosimetric equipment and Mr. Hans Hjorth for making the computer programme. This work was supported by The Danish Veterinary and Agricultural Research Council.     

Extraction and partial characterization of cellulases from expanding pea epicotyls

Etiolated pea (Pisum sativum) epicotyls synthesize a buffer-soluble cellulase (cellulase A) and a salt-soluble cellulase (cellulase B) (EC 3.2.1.4) after treatment with high (0.5%) auxin levels. Only cellulase A increased in activity after treatment with low (0.005%) auxin. Cellulase A was released into the supernatant after homogenization of tissue in dilute buffer (buffer-soluble), had a pH optimum at 5.5, was relatively thermostable, and its activity was inhibited by NaCl. Cellulase B was released by 1 m NaCl (salt-soluble) from excised tissue segments or from the insoluble residue remaining after removal of the buffer-soluble form. It had a pH optimum at 7.0, was thermolabile, and required salt for maximum activity. When subjected to polyacrylamide gel electrophoresis, the cellulase fraction released by NaCl from excised segments showed two bands of cellulase activity compared to several for the buffer-soluble fraction. Electrophoretic analysis of the buffer and salt-soluble fractions for marker enzymes indicated the presence of malate dehydrogenase activity in all fractions and glutamate dehydrogenase activity in the buffer-soluble fraction only.