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PubMed1963

The uptake and development of vaccinia virus in strain L cells followed with labeled viral deoxyribonucleic acid.

Vaccinia virus which had its DNA labeled with thymidine-H(3) was purified and used as inoculum for L cells growing in suspension. Samples taken over an 8-hour period after infection were studied by light and electron microscopic autoradiography. Within 20 minutes of its being taken up at the cell membrane in phagocytic vesicles, the outer coat of vaccinia becomes disrupted and the virus core containing the labeled DNA passes into the cytoplasmic matrix. Within 1 hour after inoculation the labeled material passes out of the cores into zones of viroplasm, where cores or remnants of cores are gathered and the label becomes more concentrated by 3 hours after inoculation. Most of the label is conserved in the viroplasm areas during the remainder of the experiment. However, 6 hours after inoculation a very small proportion of progeny virus in the cytoplasm, morphologically distinct from the cores of the inoculum, has associated with it labeled material, perhaps derived from the DNA of the inoculum.

Autoradiography↗
PubMedDate not supplied

Micromorphometric evaluation of changes in symmetry of sarcoplasmic reticulum membranes induced by vanadate.

Electron micrographs of light sarcoplasmic vesicles fixed with glutaraldehyde and osmium tetroxide followed by contrasting with uranyl acetate and lead citrate have been evaluated by registering their membrane profiles with a microdensitometer. The asymmetric arrangement of the two layers of the vesicular membrane could be ascertained by demonstrating a ratio of 1.5 for the thickness of the outer versus the inner membrane layer which is in general agreement with the proposed protein structure of the calcium transport enzyme. Treatment of the vesicles with low concentrations of vanadate (0.1 mM) results in a significant lowering of the symmetry ratio by 20% by reducing mainly the thickness of the outer membrane leaflet. Removal of the membrane lipids by treating the vesicles with phospholipase A2 and bovine serum albumin diminishes the membrane surface by 50% resulting in a significant increase of both the membrane thickness and the asymmetry ratio by 30 and 12% respectively. The vanadate induced reduction of membrane asymmetry is accentuated after delipidation indicating that the membrane lipids are not essential for the asymmetric appearance of the native membrane. The stability of the spherical form of the vesicles to delipidation implies that the transport molecules are conically shaped allowing strong mutual interactions. At a measured height of the molecule of 80 A in the membrane, the vanadate induced change in symmetry would be brought about by compensatory changes of less than 3 A of the outer (35 A) and the inner (25 A) diameter of the cone.

Animals↗
PubMed1986

Sulfhydryl groups are essential for organic anion exchange in canine renal brush-border membranes.

The effect of several sulfhydryl-modifying reagents (HgCl2, p-chloromercuribenzenesulfonic acid (PCMBS), N-ethylmaleimide) on the renal organic anion exchanger was studied. The transport of p-amino[3H]hippurate, a prototypic organic anion, was examined employing brush-border membrane vesicles isolated from the outer cortex of canine kidneys. HgCl2, PCMBS and N-ethylmaleimide inactivated p-aminohippurate transport with IC50 values of 38, 78 and 190 microM. The rate of p-aminohippurate inactivation by N-ethylmaleimide followed apparent pseudo-first-order reaction kinetics. A replot of the data gave a linear relationship between the apparent rate constants and the N-ethylmaleimide concentration with a slope of 0.8. The data are consistent with a simple bimolecular reaction mechanism and imply that one molecule of N-ethylmaleimide inactivates one essential sulfhydryl group per active transport unit. Substrate (1 mM p-aminohippurate) affected the rate of the N-ethylmaleimide (1.3 mM) inactivation: the t1/2 values for inactivation in the presence and absence of p-aminohippurate were 7.4 and 3.7 min, respectively. The results demonstrate that there are essential sulfhydryl groups for organic anion transport in the brush-border membrane. Moreover, the ability of substrate to alter sulfhydryl reactivity suggests that the latter may play a dynamic role in the transport process.

4-Chloromercuribenzenesulfonate↗
PubMed1978

Molecular structure of membrane vesicles from Escherichia coli.

The molecular architecture of membrane vesicles prepared from Escherichia coli ML 308-225 has been studied by using crossed immunoelectrophoresis, and a reference pattern of 52 discrete immunoprecipitates has been established. Progressive immunoadsorption experiments conducted with untreated control vesicles and with physically disrupted vesicles demonstrate that the membrane-associated immunogens fall into two categories: (i) those immunogens typified by ATPase (ATP phosphohydrolase, EC 3.6.1.3) and NADH dehydrogenase [NADH: (acceptor) oxidoreductase, EC 1.6.99.3] whose expression is minimal unless the vesicles are disrupted; and (ii) immunogens such as Braun's lipoprotein that are expressed to similar extents in untreated and in disrupted vesicles. A mathematical relationship between the peak area subtended by an immunoprecipitate in the crossed immuno-electrophoresis system and the quantity of vesicles used in the adsorption process has been derived. This relationship allows quantitation of the degree to which specific membrane immunogens partition between exposed and unexposed surfaces of the vesicle membrane. The results demonstrate conclusively that >95% of the membrane in the vesicle preparations is in the form of sealed sacculi with the same polarity as the intact cell. Moreover, the findings provide a strong indication that dislocation of immunogens from the inner to the outer surface of the membrane during vesicle preparation does not occur to an extent exceeding 11%.

Adenosine Triphosphatases↗
PubMed1991

Sulfhydryl groups are essential for organic cation exchange in rabbit renal basolateral membrane vesicles.

The effect of N-ethylmaleimide (NEM), an irreversible sulfhydryl modifying reagent, on the transport of organic cations in the renal basolateral membrane was examined. The studies were conducted examining the exchange of [3H]tetraethylammonium (TEA) for unlabeled TEA in basolateral membrane vesicles isolated from the outer cortex of rabbit kidneys. NEM inactivated TEA transport in a dose-dependent fashion with an IC50 value of 260 microM. The rate of TEA transport inactivation followed apparent pseudo-first-order reaction kinetics. A replot of the data gave a linear relationship between the apparent rate constants and the NEM concentration with a slope of 4.0. The data imply that inactivation involves the binding of at least four molecules of NEM per active transport unit. This is most consistent with the presence of four sulfhydryl groups at this site. The substrate TEA displayed a dose-dependent enhancement of NEM inactivation, with 50% enhancement occurring at 365 microM TEA. Another organic cation, N1-methylnicotinamide, known to share a common transport mechanism with the TEA/TEA exchanger is also capable of increasing the reactivity of sulfhydryl groups to NEM. These results demonstrate that there are essential sulfhydryl groups for organic cation transport in the basolateral membrane. In addition, the capability of organic cations to alter the susceptibility to sulfhydryl modification suggests that these groups may have a dynamic role in the transport process.

Animals↗
PubMed1999

Roles of Trp31 in high membrane binding and proinflammatory activity of human group V phospholipase A2.

Group V phospholipase A2 is a recently discovered secretory phospholipase A2 (PLA2) that has been shown to be involved in eicosanoid formation in inflammatory cells, such as macrophages and mast cells. We have demonstrated that human group V PLA2 (hsPLA2-V) can bind phosphatidylcholine (PC) membranes and hydrolyze PC substrates much more efficiently than human group IIa PLA2, which makes it better suited for acting on the outer plasma membrane (Han, S.-K., Yoon, E. T., and Cho, W. (1998) Biochem. J. 331, 353-357). In this study, we demonstrate that exogenous hsPLA2-V has much greater activity than does group IIa PLA2 to release fatty acids from various mammalian cells and to elicit leukotriene B4 formation from human neutrophils. To understand the molecular basis of these activities, we mutated two surface tryptophans of hsPLA2-V to alanine (W31A and W79A) and measured the effects of these mutations on the kinetic activity toward various substrates, on the binding affinity for vesicles and phospholipid-coated beads, on the penetration into phospholipid monolayers, and on the activity to release fatty acids and elicit eicosanoid formation from various mammalian cells. These studies show that the relatively high ability of hsPLA2-V to induce cellular eicosanoid formation derives from its high affinity for PC membranes and that Trp31 on its putative interfacial binding surface plays an important role in its binding to PC vesicles and to the outer plasma membrane.

Cell Membrane↗
PubMed1987

Protein translocation into Escherichia coli membrane vesicles is inhibited by functional synthetic signal peptides.

A synthetic peptide corresponding to the signal sequence of wild type Escherichia coli lambda-receptor protein (LamB) inhibits in vitro translocation of precursors of both alkaline phosphatase and outer membrane protein A into E. coli membrane vesicles (half-maximal inhibition at 1-2 microM). By contrast, the inhibitory effect was nearly absent in a synthetic peptide corresponding to the signal sequence from a mutant strain that harbors a deletion mutation in the LamB signal region and displays an export-defective phenotype for this protein in vivo. Two peptides derived from pseudorevertant strains that arose from the deletion mutant and exported LamB in vivo were found to inhibit in vitro translocation with effectiveness that correlated with their in vivo export ability. Controls indicated that these synthetic signal peptides did not disrupt the E. coli membrane vesicles. These results can be interpreted to indicate that the presequences of exported proteins interact specifically with a receptor either in the E. coli inner membrane or in the cytoplasmic fraction. However, biophysical data for the family of signal peptides studied here reveal that they will spontaneously insert into a lipid membrane at concentrations comparable to those that cause inhibition. Hence, an indirect effect mediated by the lipid bilayer of the membrane must be considered.

Alkaline Phosphatase↗
PubMed1987

Molecular organization of photochemical reaction complex in chromatophore membrane from Rhodospirillum rubrum as detected by immunochemical and proteolytic analyses.

The molecular organization of photochemical reaction (PR) complex in chromatophores from Rhodospirillum rubrum was studied by a combination of proteolytic analysis with proteinase K followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunochemical analysis with rabbit polyclonal antibodies against its five subunits (H, M, L, alpha, and beta). The preparations used for comparison were reaction center complex (RC) (composed of H, M, and L), PR complex, and chromatophores (closed membranous vesicles of polar lipid bilayer having PR complex buried in the membrane). 1. RC was bound with anti-H, anti-M, and anti-L antibodies, whereas PR complex and chromatophores were bound with anti-H and anti-beta antibodies, but not with the other antibodies. 2. With PR complex, H (Mr 31,000 (31K)) was rapidly degraded into two peptides with Mr of 16K and 14.5K (abbreviated as 16K and 14.5K, respectively), M (27K) into 25.5K, and beta (11K) into 10K. Significantly later, the 25.5K of M was degraded into 24K, L (23K) into 19K, and alpha (12K) into 11K. With chromatophores, H and beta were degraded in a manner similar to that with PR complex, whereas M, L, and alpha were not degraded at all. With RC, H, M, and L were rapidly degraded. 3. With RC, the activity for photooxidation of P870 (photochemical activity) was hardly affected till H, M, and L had been degraded into less than 10K, 24K, and 19K, respectively. With PR complex, the absorbance spectrum due to the bacteriochlorophylls of light-harvesting complex-1 composed of alpha and beta (LH1-Bchl) changed in parallel to the degradation of alpha or 10K (a part of beta). 4. Together with the previous results (Ueda et al. (1985) J. Biochem. 98, 1487-1498), the present findings suggest that: 1) RC is directly surrounded by 12 alpha and further by 12 beta; 2) H and beta are mostly and partially exposed, respectively, on the outer surface of the membranous vesicle; 3) a small part of M is exposed on the inner surface of the membranous vesicle.

Bacterial Chromatophores↗
PubMed1994

Ultracytochemical localization of alkaline phosphatase in swine gonadotropic cells.

In swine gonadotropic (SGT) cells, the alkaline phosphatase (APase) activity was ultracytochemically demonstrated on the outer surface of the plasma membrane and in some vesicles in the cytoplasm. The plasma membrane-associated APase activity was sporadically detected on the outer surface and was intense at the site adjacent to the next SGT cells or follicular cells. APase-positive vesicles occurred around the Golgi apparatus and in the periphery of SGT cells. Some of the vesicles positive for APase activity attached to the plasma membrane. These results suggest that APase is synthesized in SGT cells and moves to the plasma membrane.

Alkaline Phosphatase↗
PubMed1991

Diltiazem at high concentration increases the ionic permeability of biological membranes.

The effects of diltiazem, a drug which inhibits the calcium channels in cardiac muscle as well as the light-sensitive channels in photoreceptor cells, were studied on ionic fluxes in both membrane and intact cell preparations. Diltiazem nonselectively increased the ionic permeability to both anions and cations in photoreceptor rod outer segment and synaptic membrane vesicles as well as in intact erythrocytes. Under our conditions, the estimated threshold for the diltiazem effect varied between 12.5 and 200 microM. In each case the concentration dependence exhibited the sigmoidal shape characteristic of positive cooperativity. The effect of diltiazem on ionic fluxes from phospholipid vesicles were strongly influenced by phospholipid composition and membrane charge. By contrast, diltiazem inhibited the efflux of 86Rb from photoreceptor cells of intact aspartate-isolated retina, an effect opposite to that of diltiazem on ionic permeabilities in photoreceptor membrane vesicle preparations. These data raise serious doubts on the specificity of diltiazem as a calcium channel blocker or as a cGMP channel blocker when used at concentrations higher than 10 microM.

Animals↗
PubMed1996

Mucosal vaccination against schistosomiasis using liposome-associated Sm 28 kDa glutathione S-transferase.

A variety of experimental models have shown that immunization using the glutathione S-transferase from Schistosoma mansoni (Sm28GST) can induce protective immunity against this parasite. This immunity has been related to the production of Th2 type antibodies against the antigen in both mice and humans. The work presented in this paper describes the development of a mucosal immunization protocol using liposomes which is designed to promote production of specific antibodies of isotypes related to a Th2 immune response. The liposomes were multilamellar and composed of various synthetic phospholipid mixtures. The liposome vector was used to convey the Sm28GST antigen to gut associated lymphoid tissue. The association of the Sm28GST antigen with liposomes containing different lipid mixtures was initially studied. The degree of interaction of the antigen was found to increase with the hydrocarbon chain length of the lipids used. It was demonstrated that the protein was present on both the inner and the outer membranes of the liposome vesicles. It was also shown that the major epitopes of Sm28GST were accessible to specific antibodies, confirming a conservation of its main antigenic features. Additionally, enzymatic activity of the protein/liposome complex was also demonstrated, indicating a conservation of the tertiary structure of the protein. An optimal Sm28GST/ liposome complex was established and administered orally to mice. This treatment resulted in both a mucosal and systemic immune response to the antigen Sm28GST. This was demonstrated by the detection of specific IgA in gut washes and specific IgG1, IgG2b in sera. Immunization by Sm28GST/liposome complex followed by challenge with parasite showed that Sm28GST given orally in these conditions bore protective activity. This last result opens the possibility of mucosal vaccination against schistosomiasis.

Administration, Oral↗
PubMed1986

Preparation and characterization of submitochondrial fractions from adrenal cells.

A method for preparing submitochondrial fractions from adrenocortical cells was developed by adapting a procedure that has been successful with yeast mitochondria. The method is based upon osmotic swelling, sonication and centrifugation in sucrose. The preparation yields highly purified fractions of outer membrane, intermembrane space, inner membrane and a less purified fraction of matrix. Recoveries are good so that 10(7) cells yield approximately 170 micrograms of inner membrane protein and 12 micrograms of outer membrane protein. Electron microscopy shows that the outer membrane fraction consists of vesicles (0.2-0.6 micron diameter) while inner membrane appears as densely packed sheets of membranous material. Two-dimensional polyacrylamide gels (isoelectric focusing followed by electrophoresis) of all the fractions give highly reproducible patterns of protein spots with Coomassie staining. Steroidogenic proteins were found only in inner membrane fractions which were shown to contain cytochrome P-450 C27 side-chain cleavage and P-450 11 beta-hydroxylase together with adrenodoxin and adrenodoxin reductase. Inner membrane catalyzes side-chain cleavage of cholesterol (conversions to pregnenolone) and 11 beta-hydroxylation (DOC----corticosterone) when substrate and NADPH are added. The preparation yields highly purified submitochondrial fractions from Y-1 mouse adrenal tumor cells and from porcine and bovine adrenocortical mitochondria. The method has the virtue of yielding highly purified intermembrane fluid which is not true of other methods for fractionation of adrenal mitochondria. The procedure also yields cleaner preparations of the two membranes than two other published methods currently used to prepare submitochondrial fractions from adrenocortical cells.

Adrenal Glands↗
PubMed1999

Immunocytochemical evidence of vesicular localization of the orphan transporter RXT1 in the rat spinal cord.

Rxt1, a member of the Na+/Cl- orphan transporter family, exhibits numerous features suggesting a role as plasma membrane transporter. Despite numerous attempts, its substrate has not yet been identified, although immunocytochemical studies have shown that Rxt1 distribution generally matches that of glutamate or GABA. In order to further characterize Rxt1, its detailed immunocytochemical distribution in the rat spinal cord and dorsal root ganglia was studied at both light microscope and ultrastructural levels. The widespread distribution of Rxt1 in spinal cord and ganglia cannot be correlated with any known classical or peptidergic transmitter. Rxt1 is expressed in a subpopulation of glutamatergic primary afferent fibers, in large and medium-sized ganglion cells, while small glutamate cells exhibit generally no Rxt1-like immunoreactivity. In the spinal cord, Rxt1-immunoreactive cell body distribution is quite ubiquitous since Rxt1 is expressed in all laminae in various neuronal types like interneurons, some projection neurons and motoneurons. Some of these neurons are cholinergic. At the electron microscope level, the peroxidase labeling was never localized to the plasma membrane, but rather associated with different organelles including the outer membrane of small synaptic vesicles and large granular vesicles. This localization resembles that of vesicular transporters detected with the same method and suggests that Rxt1, in contrast to other Na+/Cl- transporters, is expressed on vesicles. This was confirmed using a pre-embedding silver-intensified colloidal gold method. Indeed, most gold particles appeared to be localized into the axoplasm on synaptic vesicle accumulations; only few gold particles were observed close to the plasma membrane. These results suggest that Rxt1, despite its molecular characteristics predicting a plasma membrane localization, might be a vesicular transporter.

Animals↗
PubMed1999

Adrenomedullin is upregulated in the heart and aorta during the early and late stages of sepsis.

Although circulating levels of adrenomedullin (ADM), a newly reported vasodilatory peptide with 52 amino acid residues in the human and 50 amino acid residues in the rat, are elevated during the early and late stages of sepsis, ADM levels in cardiovascular tissues and its precise localization remain to be determined. To study this, rats were subjected to sepsis by cecal ligation and puncture (CLP), followed by administration of 3 ml/100 g b.wt. normal saline to these and sham-operated animals. The heart and thoracic aorta were harvested at 5 h (i.e. the early stage of sepsis) and 20 h (late sepsis) after CLP. Tissue levels of ADM were determined by radioimmunoassay. The localization of ADM in the left ventricle and thoracic aorta was examined by using immunohistochemistry and electron microscopy techniques. The results indicated that ADM levels in the heart and thoracic aorta increased significantly at 5 h after CLP and remained elevated at 20 h after the onset of sepsis. Immunohistochemistry findings showed that ADM immunoreaction products were localized in the cytoplasm of the cardiac myocytes and aortic endothelial cells. Using electron microscopy, ADM immunoreaction products were found in the cytoplasmic matrixes. The immunostainings were also associated with the outer membranes of mitochondria and vesicles of the myocytes as well as vascular endothelial cells. It appears that the cardiovascular tissues, among other organ systems, contribute to the increased levels of plasma ADM under those conditions. Since ADM is localized in different cell populations in the heart and the large blood vessel (i.e. myocytes versus vascular endothelial cells), this peptide may play a differential role in regulating cardiac and vascular functions during sepsis as an autocrine and/or paracrine mediator.

Adrenomedullin↗
PubMed1993

Purified Escherichia coli preprotein translocase catalyzes multiple cycles of precursor protein translocation.

Escherichia coli preprotein translocase, composed of the peripheral membrane protein SecA bound at the integral membrane domain SecY/E, has been isolated and functionally reconstituted [Brundage, L., Hendrick, J. P., Schiebel, E., Driessen, A. J. M., & Wickner, W. (1990) Cell 62, 649-657]. It is not known whether this purified enzyme supports multiple turnover cycles and how its kinetics compare with translocase in inverted membrane vesicles. We now report a quantitative comparison of the translocation of the outer membrane protein A precursor (proOmpA) by purified preprotein translocase and by inner membrane vesicles. ProOmpA cross-linked to bovine pancreatic trypsin inhibitor was used for quantitative titration of the functional translocation sites. The rate of proOmpA translocation per active site in this purified system is 25% of that observed in inverted membrane vesicles. Each functional site can catalyze multiple cycles of precursor translocation. These results indicate that the purified preprotein translocase properly reconstitutes translocation.

Adenosine Triphosphatases↗
PubMed1975

Interaction between spin-labeled acyl-coenzyme A and the mitochondrial adenosine diphosphate carrier.

Spin-labeled long-chain (m,n)acyl-CoA's (general formula: CH3(CH2)mCR(CH2)nCOSCoA, where R is an oxazolidine ring containing a nitroxide) inhibit anion transports through the inner mitochondrial membrane at low concentrations as ordinary long-chain acyl-CoA's do. The inhibition constant relative to the inhibition of the ADP transport in heart mitochondria by spin-labeled palmityl-CoA and stearyl-CoA is of the order of 10-7 M, a value which is similar to that found for natural long-chain acyl-CoA's. A short-chain spin-labeled acyl-CoA (C5) showed no inhibitory effect in the range of concentrations tested (up to 30 muM). (2) (10,3)Acyl-CoA added to heart mitochondria at low concentrations exhibits spectra corresponding to an immobilized probe. The corresponding free fatty acid shows a higher freedom of motion between 0 and 30 degrees. The same differences in spectra of spin-labeled acyl-CoA and spin-labeled free fatty acid were found in inner membrane vesicles from rat liver mitochondria, but not in outer membrane preparations. (3) The selective interaction of spin-labeled acyl-CoA with the ADP carrier is indicated by the release of this interaction by specific ligands of the ADP carrier, such as ADP or ATP, carboxyatractyloside, adn bongkrekic acid. ADP (or ATP) and carboxyatractyloside rendered the spin-labeled (10,3)acyl-CoA nearly as mobile as the (10,3) free fatty acid. No effect was obtained with AMP, GDP, or UDP which are not transported by the ADP carrier. Bongkrekic acid, another specific inhibitor of the ADP carrier, was inactive when added alone; however, it was effective when added together with amounts of ADP which are ineffective per se. (4) The electron spin resonance (esr) spectrum observed at low concentrations of (10,3)acyl-CoA arises from (10,3)acyl-CoA bound to the ADP carrier. At higher concentrations the (10,3)-acy-CoA is more suggesting that the bulk of the label is also present in the lipid phase of the membrane. Spin-labeled acylCoA's incorporated into a sonicated dispersion of lipids extracted from heart mitochondria exhibited similar mobile spectra. (5) When the oxazolidine ring is moved down the hydrocarbon chain of the acyl-CoA, the binding features tended to disappear. Whereas nitroxide-protein interactions could be easily measured with the (10,3)acyl-CoA and the (7,6)acyl-CoA, much less or even no significant interactions could be detected with the (5,10)acyl-CoA or the (1,14)acyl-CoA. (6) The above results suggest that spin-labeled long-chain acylCoA added to mitochondria binds by its polar moiety to the ADP carrier. The acyl chain interacts with the ADP carrier protein over a length of 10-15 A. The remaining portion of the acyl chain experiences a fluid lipid environment.

Adenosine Diphosphate↗
PubMed1977

Proton spin-lattice relaxation of retinal rod outer segment membranes and liposomes of extracted phospholipids.

A large fraction of the phospholipid protons of bovine retinal rod outer segment (ROS) disc membrane vesicles yield well-resolved nuclear magnetic resonance lines near physiological temperature. The spin-lattice (T1) relaxation rates of the resolved sharp resonance of ROS disc membranes appear biphasic above 10 degrees C. The rate of the more rapidly relaxing component of each resonance matches closely the relaxation rate of the corresponding resonances of liposomes of purified ROS phospholipids. The slowly relaxing component of each disc membrane resonance is most likely due to phospholipids whose motion is affected by rhodopsin. The primary difference in the relaxation behavior of phospholipids in the ROS membrane vesicles and ROS liposomes appears to be in T1, rather than T2, since the corresponding sharp resonances of both preparations have similar linewidths. These observations suggest that the interaction of rhodopsin with the more fluid membrane phospholipids predominantly affects relatively high frequency segmental motions, which determine T1, while having minimal effects on the lower frequency segmental motions, which influence T2. This conclusion can be rationalized by assuming that a substantial fraction of the interacting phospholipids are relatively fluid with respect to less frequent, larger amplitude segmental motions, but that the more frequent segmental motions (such as beta-coupled trans-gauche isomerizations) are significantly restricted by interaction with protein.

Animals↗
PubMed1961

Microtubulation of the inner membrane of the nuclear envelope.

In the course of a light and electron microscopy study of spermatogenesis in the European crayfish, Astacus fluviatilis, spermatocytes of abnormal appearance were observed in two instances in individuals that had passed the mating period. The electron microscope showed that the inner membrane of the nuclear envelope of these cells was erupting into a mass of microtubules, 15 to 18 mmicro in diameter and 0.5 micro or more in length, while the outer membrane transformed into cytoplasmic vesicles. Stages in the formation of these novel processes were followed. The plasma membrane of the affected cells was seen in some cases to erupt into similar although shorter microtubules. It is concluded that the phenomenon is part of a degenerative process in which the spermatocytes are being absorbed by sustentacular cells. It is suggested that the observations provide further evidence for a fundamental functional as well as a morphological similarity between the membranes bounding the nucleus and the plasma membrane.

Cell Membrane↗