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At least 1,117 records · Page 62Linked to original sources
PubMed2000

Clinical application of the two-layer (University of Wisconsin solution/perfluorochemical plus O2) method of pancreas preservation before transplantation.

BACKGROUND: The two-layer method [University of Wisconson solution (UW)/perfluorochemical plus O2] for pancreas preservation has been demonstrated to be superior to simple UW storage alone in the canine model. For the first time, we applied the two-layer method to clinical whole-pancreas transplantation. METHODS: Pancreases were placed in the two-layer method in 10 cases and UW alone in 44 cases before transplant. The mean cold ischemic time was 16.5 hr in the two-layer group versus 18.1 hr in the UW group (P=NS). We compared the condition of graft at the time of reperfusion, and then 3 months posttransplant graft function and complications. RESULTS: At the time of reperfusion, no grafts in the two-layer group were edematous, compared with 10(23.3%) of 43 in the UW group (P=0.18). Seven (70%) of 10 grafts in the two-layer group obtained the best overall quality score, compared with 24(57.1%) of 42 in the UW group (P=0.72). Nine (90%) of 10 recipients in the two-layer group became insulin-independent during hospitalization, compared with 31(70.5%) of 44 in the UW group (P=0.26). Time to insulin independence was no different between the two groups. No pancreas grafts preserved by the two-layer method suffered acute rejection. Conclusions. The two-layer preservation method is feasible in human clinical transplantation. It was at least equivalent and may be superior to UW alone in both morphologic and functional assessment of the transplanted pancreas.

Adenosine↗
PubMed2002

Differences by quadrant of retinal nerve fiber layer thickness in healthy eyes.

PURPOSE: The purpose of this study was to determine the distribution of retinal nerve fiber layer thickness by quadrant in healthy eyes. PATIENTS AND METHODS: Forty subjects with healthy eyes were included in the study. A complete ophthalmic examination was performed, including determination of visual fields by automated perimetry. The subjects had no family history of retinal disease or glaucoma. Forty right eyes and 40 left eyes were measured. Retinal nerve fiber layer thickness was measured using simultaneous stereophotographs with stereophotogrammetry at the disc margin. For the total disc and four quadrants, absolute retinal nerve fiber layer thickness and optic disc area was determined using a magnification correction formula. RESULTS: Comparison of the quadrants showed that the retinal nerve fiber layer thicknesses of the superior, inferior, and nasal quadrants were significantly thicker than the temporal quadrant (P = 0.00006 for right and left eyes). No significant differences were observed between the superior, inferior, and nasal quadrants in the right eye. In the left eye, the superior retinal nerve fiber layer thickness was significantly greater than the inferior (P = 0.028) and nasal retinal nerve fiber layer thicknesses (P = 0.00006), while the inferior was not significantly different from the nasal. No significant difference in quadrant retinal nerve fiber layer thickness was noted between eyes. CONCLUSIONS: Measurements of retinal nerve fiber layer thickness in healthy eyes show the thinnest quadrant to be the temporal, with the other three quadrants having similar thicknesses. This pattern corresponds to the histologic measurements of retinal nerve fiber layer thickness.

Adult↗
PubMed2000

Diffusion of waves in a layer with a rough interface

Sound trapped between the rough boundaries of a statistically homogeneous layer can exhibit diffusive behavior which influences the reverberation of a pulsed signal. If the interfaces of the layer can transmit sound, then eventually sound within the layer will be lost and there will be no diffusion. Nevertheless, if the transmission to the exterior of the layer is weak, there will be a remnant of diffusion. This paper examines the description of this kind of quasidiffusive behavior for sound which impinges on the rough interface of such a layer from outside the layer. As in the case of diffuse light scattering by particles in suspension, the diffusion constant is renormalized according to the delay required to build up resonant energy in the layer. In addition, when there is a density contrast between the interior and exterior of the layer, or when there is dispersion, the diffusion constant has another correction associated with energy flux within the layer.

Journal Article↗
PubMed2006

Layered Wyner-Ziv video coding.

Following recent theoretical works on successive Wyner-Ziv coding (WZC), we propose a practical layered Wyner-Ziv video coder using the DCT, nested scalar quantization, and irregular LDPC code based Slepian-Wolf coding (or lossless source coding with side information at the decoder). Our main novelty is to use the base layer of a standard scalable video coder (e.g., MPEG-4/H.26L FGS or H.263+) as the decoder side information and perform layered WZC for quality enhancement. Similar to FGS coding, there is no performance difference between layered and monolithic WZC when the enhancement bitstream is generated in our proposed coder. Using an H.26L coded version as the base layer, experiments indicate that WZC gives slightly worse performance than FGS coding when the channel (for both the base and enhancement layers) is noiseless. However, when the channel is noisy, extensive simulations of video transmission over wireless networks conforming to the CDMA2000 1X standard show that H.26L base layer coding plus Wyner-Ziv enhancement layer coding are more robust against channel errors than H.26L FGS coding. These results demonstrate that layered Wyner-Ziv video coding is a promising new technique for video streaming over wireless networks.

Algorithms↗
PubMed2005

Dopamine D1-like receptor modulates layer- and frequency-specific short-term synaptic plasticity in rat prefrontal cortical neurons.

The mesocortical dopamine (DA) input to the prefrontal cortex (PFC) is crucial for processing short-term working memory (STWM) to guide forthcoming behavior. Short-term plasticity-like post-tetanic potentiation (PTP, < 3 min) and short-term potentiation (STP, < 10 min) may underlie STWM. Using whole-cell voltage-clamp recordings, mixed glutamatergic excitatory postsynaptic currents (EPSCs) evoked by layer III or layer V stimulation (0.5 or 0.067 Hz) were recorded from layer V pyramidal neurons. With 0.5 Hz basal stimulation of layer III, brief tetani (2 x 50 Hz) induced a homosynaptic PTP (decayed: approximately 1 min). The D1-like antagonist SCH23390 (1 microm) increased the PTP amplitude and decay time without inducing changes to the tetanic response. The tetani may evoke endogenous DA release, which activates a presynaptic D1-like receptor to inhibit glutamate release to modulate PTP. With a slower (0.067 Hz) basal stimulation, the same tetani induced STP (lasting approximately 4 min, but only at 2x intensity only) that was insignificantly suppressed by SCH23390. With stimulation of layer-V-->V inputs at 0.5 Hz, layer V tetani yielded inconsisitent responses. However, at 0.067 Hz, tetani at double the intensity resulted in an STP (lasting approximately 6 min), but a long-term depression after SCH23390 application. Endogenous DA released by tetanic stimulation can interact with a D1-like receptor to induce STP in layer V-->V synapses that receive slower (0.067 Hz) frequency inputs, but suppresses PTP at layer III-->V synapses that receive higher (0.5 Hz) frequency inputs. This D1-like modulation of layer- and frequency-specific synaptic responses in the PFC may contribute to STWM processing.

Animals↗
PubMed1997

Applications of S-layers.

The wealth of information existing on the general principle of S-layers has revealed a broad application potential. The most relevant features exploited in applied S-layer research are: (i) pores passing through S-layers show identical size and morphology and are in the range of ultrafiltration membranes; (ii) functional groups on the surface and in the pores are aligned in well-defined positions and orientations and accessible for binding functional molecules in very precise fashion; (iii) isolated S-layer subunits from many organisms are capable of recrystallizing as closed monolayers onto solid supports at the air-water interface, on lipid monolayers or onto the surface of liposomes. Particularly their repetitive physicochemical properties down to the subnanometer scale make S-layers unique structures for functionalization of surfaces and interfaces down to the ultimate resolution limit. The following review focuses on selected applications in biotechnology, diagnostics, vaccine development, biomimetic membranes, supramolecular engineering and nanotechnology. Despite progress in the characterization of S-layers and the exploitation of S-layers for the applications described in this chapter, it is clear that the field lags behind others (e.g. enzyme engineering) in applying recent advances in protein engineering. Genetic modification and targeted chemical modification would allow several possibilities including the manipulation of pore permeation properties, the introduction of switches to open and close the pores, and the covalent attachment to surfaces or other macromolecules through defined sites on the S-layer protein. The application of protein engineering to S-layers will require the development of straightforward expression systems, the development of simple assays for assembly and function that are suitable for the rapid screening of numerous mutants and the acquisition of structural information at atomic resolution. Attention should be given to these areas in the coming years.

Bacteria↗
PubMed1980

Comparative study of the smooth muscle layers of the rabbit duodenum.

1. Intracellular electrodes were used to compare the electrical activity of smooth muscle cells from the longitudinal and circular layers of the rabbit duodenum and their responses to stimulation of the intramural nerves. 2. The longitudinal muscle cells had an average membrane potential of 52 mV when measured between slow waves. Spontaneous action potentials were superimposed on every slow wave. 3. The circular muscle cells had a higher membrane potential of 64 mV although the amplitude of the slow waves was similar to that of the longitudinal muscle cells. Spontaneous action potentials were rarely observed in the circular muscle cells. 4. Lowering the temperature from 36 to 30 degrees C caused a reduction in the membrane potential of the longitudinal muscle cells but not in the circular muscle cells. However, the amplitude of the slow waves of the two layers was reduced to a similar extent. 5. Electrical stimulation produced advances of the slow wave cycles if the stimuli were applied between slow waves. The responses of the cells from the two layers were identical. 6. Under normal conditions, electrotonic coupling was observed only in cells of the muscle layer whose long axis was aligned along the direction of the applied current. 7. In the longitudinal muscle, cholinergic responses blocked by atropine were observed. Inhibitory potentials were the predominant response in the circular muscle. 8. Excitatory responses were recorded in 9% of the circular muscle cells. "Off' excitation following termination of a train of repetitive stimulation pulses was also observed. 9. The differences in membrane potentials, spontaneous spiking activities, neural responses, and the failure to demonstrate good electrotonic coupling between the muscle layers suggest that there was poor electrotonic interaction between the muscle layers. The amplitude of the slow waves of the two layers was nevertheless similar. Thus the validity of the hypothesis that slow waves were transmitted passively from the longitudinal layer into the circular layer through electrotonic coupling must be questioned.

Animals↗
PubMed2006

Efficacy and connectivity of intracolumnar pairs of layer 2/3 pyramidal cells in the barrel cortex of juvenile rats.

Synaptically coupled layer 2/3 (L2/3) pyramidal neurones located above the same layer 4 barrel ('barrel-related') were investigated using dual whole-cell voltage recordings in acute slices of rat somatosensory cortex. Recordings were followed by reconstructions of biocytin-filled neurones. The onset latency of unitary EPSPs was 1.1 +/- 0.4 ms, the 20-80% rise time was 0.7 +/- 0.2 ms, the average amplitude was 1.0 +/- 0.7 mV and the decay time constant was 15.7 +/- 4.5 ms. The coefficient of variation (c.v.) of unitary EPSP amplitudes decreased with increasing EPSP peak and was 0.33 +/- 0.18. Bursts of APs in the presynaptic pyramidal cell resulted in EPSPs that, over a wide range of frequencies (5-100 Hz), displayed amplitude depression. Anatomically the barrel-related pyramidal cells in the lower half of layer 2/3 have a long apical dendrite with a small terminal tuft, while pyramidal cells in the upper half of layer 2/3 have shorter and often more 'irregularly' shaped apical dendrites that branch profusely in layer 1. The number of putative excitatory synaptic contacts established by the axonal collaterals of a L2/3 pyramidal cell with a postsynaptic pyramidal cell in the same column varied between 2 and 4, with an average of 2.8 +/- 0.7 (n = 8 pairs). Synaptic contacts were established predominantly on the basal dendrites at a mean geometric distance of 91 +/- 47 mum from the pyramidal cell soma. L2/3-to-L2/3 connections formed a blob-like innervation domain containing 2.8 mm of the presynaptic axon collaterals with a bouton density of 0.3 boutons per mum axon. Within the supragranular layers of its home column a single L2/3 pyramidal cell established about 900 boutons suggesting that 270 pyramidal cells in layer 2/3 are innervated by an individual pyramidal cell. In turn, a single pyramidal cell received synaptic inputs from 270 other L2/3 pyramidal cells. The innervation domain of L2/3-to-L2/3 connections superimposes almost exactly with that of L4-to-L2/3 connections. This suggests that synchronous feed-forward excitation of L2/3 pyramidal cells arriving from layer 4 could be potentially amplified in layer 2/3 by feedback excitation within a column and then relayed to the neighbouring columns.

Action Potentials↗
PubMed2001

Point load wave excitation in multi-layered solids: experiments and model verification.

Studies of transient wave propagation in a single plate, a two-layer plate structure, and a two-layer-on-a-half-space structure are reported. Experimental results are used to verify the accuracy of a new model for wave propagation in layered solids. The experiments are performed using point load excitation and point detection at the surface of the layered structure. The basis of the new wave propagation model is first introduced. Then, experiments performed on a single plate are described. Results from different wave sources, plate materials, and wave sensors are compared with each other and with computed results from the model. The transient source function for a pencil-lead-break wave source is obtained. Next, the results of experiments performed on a two-layer plate structure (aluminum bonded to stainless steel) are reported. The cases of stainless steel atop aluminum and aluminum atop stainless steel are considered. The effects of the second layer on the transient displacement at the top surface are discussed. Finally, a two-layer-on-a-half-space structure consisting of a stainless steel plate as the top layer, an aluminum plate as the second layer and a thick acrylic resin block as the half-space is studied. The obtained experimental transient measurements agree with the computed results for all cases, thus verifying the accuracy of the model.

Journal Article↗
PubMed1998

A new member of the S-layer protein family: characterization of the crs gene from Campylobacter rectus.

Strains of the periodontal pathogen Campylobacter rectus express a 150- to 166-kDa protein on their cell surface. This protein forms a paracrystalline lattice, called the surface layer (S-layer), on the outer membrane of this gram-negative bacterium. To initiate a genetic analysis of the function of the S-layer in the pathogenesis of C. rectus, we have cloned and characterized its gene. The S-layer gene (crs) from C. rectus 314 encodes a cell surface protein which does not have a cleaved signal peptide at its amino terminus. Although the amino acid sequence deduced from the crs gene has 50% identity with the amino-terminal 30 amino acids of the four S-layer proteins from Campylobacter fetus, the similarity decreases to less than 16% over the rest of the protein. Thus, the crs gene from C. rectus encodes a novel S-layer protein whose precise role in pathogenesis may differ from that of S-layer proteins from other organisms. Southern and Northern blot analyses with probes from different segments of the crs gene indicate that the S-layer gene is a single-copy, monocistronic gene in C. rectus. RNA end mapping and sequence analyses were used to define the crs promoter; there is an exact match to the Escherichia coli -10 promoter consensus sequence but only a weak match to the -35 consensus element. Southern blots of DNA from another strain of C. rectus, ATCC 33238, demonstrated that the crs gene is also present in that strain but that there are numerous restriction fragment length polymorphisms in the second half of the gene. This finding suggests that the carboxy halves of the S-layer proteins from strains 314 and 33238 differ. It remains to be determined whether the diversities in sequence are reflected in functional or antigenic differences important for the pathogenesis of different C. rectus isolates.

Amino Acid Sequence↗
PubMed2000

Roles of the surface layer proteins of Campylobacter fetus subsp. fetus in ovine abortion.

The role of the surface (S)-layer proteins of Campylobacter fetus subsp. fetus has been investigated using an ovine model of abortion. Wild-type strain 23D induced abortion in up to 90% of pregnant ewes challenged subcutaneously. Isolates recovered from both dams and fetuses expressed S-layer proteins with variable molecular masses. The spontaneous S-layer-negative variant, strain 23B, neither colonized nor caused abortions in pregnant ewes. A series of isogenic sapA and recA mutants, derived from 23D, also were investigated in this model. A mutant (501 [sapA recA(+)]) caused abortion in one of five challenged animals and was recovered from the placenta of a second animal. Another mutant (502 [sapA recA]) with no S-layer protein expression caused no colonization or abortions in challenged animals but caused abortion when administered intraplacentally. Mutants 600(2) and 600(4), both recA, had fixed expression of 97- and 127-kDa S-layer proteins, respectively. Two of the six animals challenged with mutant 600(4) were colonized, but there were no abortions. As expected, all five strains recovered expressed a 127-kDa S-layer protein. In contrast, mutant 600(2) was recovered from the placentas of all five challenged animals and caused abortion in two. Unexpectedly, one of the 16 isolates expressed a 127-kDa rather than a 97-kDa S-layer protein. Thus, these studies indicate that S-layer proteins appear essential for colonization and/or translocation to the placenta but are not required to mediate fetal injury and that S-layer variation may occur in a recA strain.

Abortion, Veterinary↗
PubMed1976

Substructure and in vitro assembly of the outer, structured layer of Spirillum serpens.

Electron micrographs of disintegrating units of the outer, structured (HP) layer of Spirillum serpens and of the isolated protein obtained from the HP layer revealed V- and Y-shaped and linear profiles. Interpretation of these forms, influenced by the seemingly trimeric form of the isolated protein and by biochemical data, suggested that the protein subunits were identical and Y shaped. A model is proposed for the assembly of the Y-shaped subunits to form a hexagon composed of two triads (three Y-shaped subunits each). The isolated protein adsorbed to a template of wall fragments (basal layer) to the same degree (over 90%) in high concentrations of Na+, K+ (5 X 10(-2) M), Ca2+, Sr2+, and Mg2+ (10(-2) M). At a lower concentration (4 x 10(-5) M) of the cations there was differential adsorption of the protein. Adsorption to the template in the presence of each cation, followed by dilution, also led to differential release of the protein. The adsorption of the protein to the basal layer was correlated with reassembly of the HP layer on the template. The mechanisms seem to be: (i) an ionic strength-dependent reassembly, which results in an HP layer loosely attached to the template (this layer is easily dissociated by decreasing the ionic strength); and (ii) a cation-specific (Ca2+ or Sr2+, but not Mg2+, Na+, or K+) mechanism independent of ionic strength. In this latter case, the specific cations presumably form strong noncovalent "salt" linkages between triads and the basal layer, enabling stable hexagons and the HP layer to be formed.

Adsorption↗
PubMed1982

Expansion of the tetragonally arrayed cell wall protein layer during growth of Bacillus sphaericus.

The outermost layer of the cell wall of Bacillus sphaericus strain P-1 is a tetragonally arrayed structure (T-layer) which is assembled from a single polypeptide. No turnover of T-layer was detected during growth of cultures. In contrast, the turnover of peptidoglycan was between 20 and 25% per generation. The sites of deposition of new T-layer on the cell surface were identified by the indirect fluorescent antibody technique, which labeled old T-layer, and by the reverse technique, which labeled new T-layer. These experiments demonstrated that the major area of T-layer deposition was a band at the site of an incipient cell division. This band subsequently split and covered the new pole of each progeny cell. Little or no T-layer was inserted into existing poles. In addition, multiple bands of new T-layer, which probably accommodate cell elongation, were inserted along the lateral surface of the cell.

Bacillus↗
PubMed1994

Isolation of two physiologically induced variant strains of Bacillus stearothermophilus NRS 2004/3a and characterization of their S-layer lattices.

During growth of Bacillus stearothermophilus NRS 2004/3a in continuous culture on complex medium, the chemical properties of the S-layer glycoprotein and the characteristic oblique lattice were maintained only if glucose was used as the sole carbon source. With increased aeration, amino acids were also metabolized, accompanied by liberation of ammonium and by changes in the S-layer protein. Depending on the stage of fermentation at which oxygen limitation was relieved, two different variants, one with a more delicate oblique S-layer lattice (variant 3a/V1) and one with a square S-layer lattice (variant 3a/V2), were isolated. During the switch from the wild-type strain to a variant or from variant 3a/V2 to variant 3a/V1, monolayers of two types of S-layer lattices could be demonstrated on the surfaces of single cells. S-layer proteins from variants had different molecular sizes and a significantly lower carbohydrate content than S-layer proteins from the wild-type strain did. Although the S-layer lattices from the wild-type and variant strains showed quite different protein mass distributions in two- and three-dimensional reconstructions, neither the amino acid composition nor the pore size, as determined by permeability studies, was significantly changed. Peptide mapping and N-terminal sequencing results strongly indicated that the three S-layer proteins are encoded by different genes and are not derived from a universal precursor form.

Amino Acids↗
PubMed1994

Domain structure of the Acetogenium kivui surface layer revealed by electron crystallography and sequence analysis.

The three-dimensional structure of the Acetogenium kivui surface layer (S-layer) has been determined to a resolution of 1.7 nm by electron crystallographic techniques. Two independent reconstructions were made from layers negatively stained with uranyl acetate and Na-phosphotungstate. The S-layer has p6 symmetry with a center-to-center spacing of approximately 19 nm. Within the layer, six monomers combine to form a ring-shaped core surrounded by a fenestrated rim and six spokes that point towards the axis of threefold symmetry and provide lateral connectivity to other hexamers in the layer. The structure of the A. kivui S-layer protein is very similar to that of the Bacillus brevis middle wall protein, with which it shares an N-terminal domain of homology. This domain is found in several other extracellular proteins, including the S-layer proteins from Bacillus sphaericus and Thermus thermophilus, Omp alpha from Thermotoga maritima, an alkaline cellulase from Bacillus strain KSM-635, and xylanases from Clostridium thermocellum and Thermoanaerobacter saccharolyticum, and may serve to anchor these proteins to the peptidoglycan. To our knowledge, this is the first example of a domain conserved in several S-layer proteins.

Amino Acid Sequence↗
PubMed1995

The S-layer from Bacillus stearothermophilus DSM 2358 functions as an adhesion site for a high-molecular-weight amylase.

The S-layer lattice from Bacillus stearothermophilus DSM 2358 completely covers the cell surface and exhibits oblique symmetry. During growth of B. stearothermophilus DSM 2358 on starch medium, three amylases with molecular weights of 58,000, 98,000, and 184,000 were secreted into the culture fluid, but only the high-molecular-weight enzyme was found to be cell associated. Studies of interactions between cell wall components and amylases revealed no affinity of the high-molecular-weight amylase to isolated peptidoglycan. On the other hand, this enzyme was always found to be associated with S-layer self-assembly products or S-layer fragments released during preparation of spheroplasts by treatment of whole cells with lysozyme. The molar ratio of S-layer subunits to the bound amylase was approximately 8:1, which corresponded to one enzyme molecule per four morphological subunits. Immunoblotting experiments with polyclonal antisera against the high-molecular-weight amylase revealed a strong immunological signal in response to the enzyme but no cross-reaction with the S-layer protein or the smaller amylases. Immunogold labeling of whole cells with anti-amylase antiserum showed that the high-molecular-weight amylase is located on the outer face of the S-layer lattice. Because extraction of the amylase was possible without disintegration of the S-layer lattice into its constituent subunits, it can be excluded that the enzyme is incorporated into the crystal lattice and participates in the self-assembly process. Affinity experiments strongly suggest the presence of a specific recognition mechanism between the amylase molecules and S-layer protein domains either exposed on the outermost surface or inside the pores. In summary, results obtained in this study confirmed that the S-layer protein from B. stearothermophilus DSM 2358 functions as an adhesion site for a high-molecular-weight amylase.

Amylases↗
PubMed1997

Variation of nerve fibre layer thickness measurements with age and ethnicity by scanning laser polarimetry.

AIMS: Scanning laser polarimetry is a new technique allowing quantitative analysis of the retinal nerve fibre layer in vivo. This technique was employed to investigate the variation of the retinal nerve fibre layer thickness in a group of normal subjects of different ages and ethnic groups. METHODS: 150 normal volunteers of different ages and ethnic groups were recruited for this study. Three consecutive 15-degree polarimetric maps were acquired for each subjects. Nerve fibre layer thickness measurements were obtained at 1.5 disc diameters from the optic nerve. Four 90-degree quadrants were identified. RESULTS: The mean nerve fibre layer thickness varied from a minimum of 55.4 microns to a maximum of 105.3 microns, with a mean thickness value of 78.2 (SD 10.6) microns. Superior and inferior quadrants showed a comparatively thicker nerve fibre layer than nasal and temporal quadrants. Retinal nerve fibre layer thickness is inversely correlated with age (p < 0.001). White people showed thicker nerve fibre layers than Afro-Caribbeans (p = 0.002). CONCLUSION: The results indicate a progressive reduction of the nerve fibre layer thickness with increasing age. This may be due to a progressive loss of ganglion axons with age as suggested in postmortem studies. A racial difference in nerve fibre layer thickness is present between whites and Afro-Caribbeans.

Adolescent↗
PubMed1976

Superficial cell-wall layers on Spirillum "Ordal" and their in vitro reassembly.

The cell envelope of Sporillum sp. strain "Ordal" (possibly a variety of S. anulus) demonstrated multiple superficial wall layers which were diverse in their macromolecular arrays. Negative staining and freeze-etching techniques revealed an outer hexagonally packed layer and an inner tetragonally packed layer. However, both thin sections and freeze-etched cleavages of the wall showed that each of these regular structures rested upon a backing layer, and that there was a delicate amorphous layer overlying the outer hexagonal array. Rotary integration, optical deffraction, and reconstruction of image were used to clarify measurements of each array and to verify the validity of a diagrammatic model of the outer hexagonal system. The integrity of these layers required suitable cations (Ca2+ appeared essential) and pH (pH less than or equal to 4.6 dissociated most superficial layers). These observations aided in the development of a low-pH cationic-substitution technique, in which Na+ replaced essential Ca2+, for extraction of the layers from the cell surface. Dialysis to remove Na+ and restoration of Ca2+ initiated in vitro reassembly of the superficial layer components until regularly structured assembly products were formed.

Calcium↗