Lacunar syndromes due to brainstem infarct and haemorrhage

Nine patients with brainstem infarct and two with brainstem haemorrhage presented with pure motor stroke, pure supranuclear facial palsy, sensorimotor stroke or ataxic hemiparesis. Despite the clinical similarity with hemispheric lacunes, brainstem infarcts causing lacunar syndromes probably have a greater tendency to progress. Small brainstem haemorrhages should also be considered as a cause of lacunar syndromes and the difficulty in differentiating them from small infarcts without CT is emphasised.

Adenosine kinase deficiency in tritiated deoxyadenosine-resistant mouse S49 lymphoma cell lines

Mutant sublines were derived of S49 mouse T-lymphoma cells that were resistant to tritiated deoxyadenosine. Twenty-five isolates that were selected in 1 microCi/ml of the nucleoside were cross-resistant to 6-thioguanine, were sensitive to HAT (hypoxanthine, aminopterin, and thymidine), and contained less than 1% of hypoxanthine phosphoribosyltransferase activity in wild-type cells. One of the mutant clones, S49-dA2, was further subjected to selection in a medium containing 2 microCi/ml tritiated deoxyadenosine and 1 microgram/ml deoxycoformycin, an inhibitor of adenosine deaminase. All resistant subclones were cross-resistant to tubercidin, 6-methylmercaptopurine riboside, and arabinosyladenine. One of the subclones, S49-12, was completely devoid of adenosine kinase and was partially deficient in deoxyadenosine kinase. This subclone, however, contained wild-type levels of deoxycytidine kinase. DEAE chromatography of the wild-type cell extracts revealed two deoxyadenosine phosphorylating activities, one of which coeluted with adenosine kinase and was the enzyme missing in S49-12. The other species phosphorylated both deoxyadenosine and deoxycytidine, of which deoxycytidine was the preferred substrate.

Scanning calorimetry reveals a new phase transition in L-alpha-dipalmitoylphosphatidylcholine

We report a new phase transition in fully hydrated dispersions of dipalmitoylphosphatidylcholine (DPPC). This new transition, called the sub-subtransition, exhibits a transition enthalpy of 0.25 kcal/mol with a Tm at 6.8 degrees C. Unlike the subtransition, no extended low temperature incubation is required to observe the sub-subtransition. This new sub-subgel (SGII) phase may be a precursor to the subgel (SGI) phase, and this discovery is discussed in relation to the current knowledge regarding the polymorphic gel phases of both ester- and ether-linked lipids with identical acyl chains.

Characterization of the cell surface heterodimer VLA-4 and related peptides

A monoclonal antibody (B-5G10) was produced which specifically recognizes the Mr 150,000/130,000 VLA-4 complex on the surface of human cells. Cross-linking studies indicated that the Mr 150,000 alpha 4 subunit of VLA-4 is in noncovalent 1:1 association with the Mr 130,000 VLA beta subunit. In the absence of cross-linking, the VLA-4 alpha 4 beta subunit complex was easily dissociated, especially in Nonidet P-40 detergent, or at elevated pH (above 8.0). Studies of dissociated subunits showed that B-5G10 recognizes an epitope on the Mr 150,000 alpha 4 subunit of VLA-4, whereas the beta subunit is immunologically identical to the Mr 130,000 beta subunit common to all VLA heterodimers. VLA-4 is widely distributed on hematopoietic cells, including thymocytes, peripheral blood lymphocytes, monocytes, activated T cells, T and B lymphoblastoid cell lines, and myeloid cell lines. However, VLA-4 is only weakly expressed on most adherent cell lines tested. Immunoprecipitates of VLA-4 often contain additional proteins of Mr 80,000 and Mr 70,000. These are probably derived from the Mr 150,000 alpha 4 subunit because: 1) they are both recognized by anti-alpha 4 sera, but not anti-beta sera; 2) the sum of their sizes is equal to the size of alpha 4; 3) they are selectively coexpressed with alpha 4 and not other VLA alpha subunits; 4) the Mr 80,000 protein has an identical NH2-terminal sequence to alpha 4; 5) like alpha 4, the Mr 70,000 and 80,000 peptides can variably associate with the VLA beta subunit; and 6) trypsin appears to cleave the Mr 150,000 alpha 4 subunit into products of Mr 70,000 and 80,000.

Transient expression system to measure the efficiency of vaccinia promoter regions

A transient expression system has been developed to compare the relative efficiency of expression of various vaccinia virus DNA sequences containing transcriptional regulatory elements. A plasmid vector was constructed containing both the Escherichia coli galactokinase gene (galK) and the guanine phosphoribosyltransferase gene (gpt). To direct the expression of gpt within this vector, a vaccinia virus promoter region was isolated from the HindIII-F fragment of the genome and inserted 5' to gpt coding sequence. Four unique cloning sites in front of galK allow simple and precise fusion of various vaccinia virus DNA fragments that contain the regulatory site of interest to galK. Sequences containing promoter regions were ligated to the coding segment of the galK to create four recombinant plasmids, which were introduced into vaccinia virus-infected cells by transfection. Both galK and gpt were thus expressed under the control of vaccinia virus transcriptional units, and the enzymatic activities were measured in the same cell extract with a filter-binding assay. The major advantage of this transient expression system is that the variations in galK expression are always measured relative to the internal gpt standard. Changes in the galK/gpt ratio resulting from different vaccinia promoters of galK are thus a quantitative measurement of promoter strength.

Fibronectin receptor structures in the VLA family of heterodimers

Multiple cell surface proteins of relative molecular mass 115,000-155,000 (Mr 115K-155K) have been implicated as receptors mediating adhesion to extracellular matrix proteins. But the organization and relatedness of these peptides has remained unclear. In separate studies, the 'very late antigens' VLA-1 (Mr 210K/130K) and VLA-2 (Mr 160K/130K) were initially characterized as surface heterodimers appearing 2-4 weeks after in vitro stimulation of human T cells. Three more VLA heterodimers have since been discovered, which, like VLA-1 and VLA-2, are each composed of unique alpha-subunits in association with a common 130K beta subunit. This paper shows that the common VLA beta-subunit is equivalent to subunits found in structures with known fibronectin and laminin receptor activity, and that VLA-3 and VLA-5 are similar or identical to these previously defined receptors for adhesion molecules. Antibody blocking studies confirmed that at least some of the widely distributed VLA proteins of previously unknown function are involved in cell adhesion to fibronectin and laminin. We suggest that the VLA family of receptors may provide cells with multiple independent substrate adhesion capabilities.

The VLA protein family. Characterization of five distinct cell surface heterodimers each with a common 130,000 molecular weight beta subunit

The family of human cell surface heterodimers which includes VLA-1 and VLA-2 is now shown to include three additional heterodimers, here called VLA-3, VLA-4, and VLA-5. Each of these separate VLA structures is composed of a distinct alpha subunit (Mr 110,000-200,000 nonreduced) noncovalently associated with a common beta subunit (Mr 110,000 nonreduced). Chemical cross-linking experiments provided evidence that each VLA complex exists predominantly as a 1:1 alpha beta heterodimer. The VLA proteins are widely distributed, with one or more of the heterodimers present on nearly all cell types tested. Evidence for five distinct VLA alpha subunits was obtained from differences observed in antibody recognition, cell distribution patterns, two-dimensional gel analyses, and V8 protease cleavage patterns. On the other hand, the beta subunit present in each heterodimer was immunochemically and electrophoretically indistinguishable, and yielded identical V8 cleavage fragments. Immunoblotting experiments revealed that besides the Mr 110,000 beta normally seen, another beta protein was present that is smaller in size (Mr 90,000 nonreduced), altered or deficient in glycosylation, and not available for cell surface radiolabeling.

Kinetics of allophycocyanin's trimer-monomer equilibrium

Kinetic studies of the dissociation of allophycocyanin trimers to monomers have been performed by using stopped-flow techniques. The dissociation was monitored by two techniques: by light scattering to observe the molecular weight changes directly and by 650-nm absorbance to observe the linkage of quaternary structure to spectra. The light-scattering experiments showed a simple exponential decay of trimers to monomers with a dissociation constant of 0.23 s-1. The absorption changes were complex, with two processes occurring. The faster absorption change appeared to be almost simultaneous with the molecular weight change (about 0.27 s-1) and was perhaps totally coordinated with it. The slower absorption change (0.071 s-1) was possibly a result of a conformational change in the chromophore arising during the conversion from newly dissociated monomers to equilibrium monomers.

Use of the monoclonal antibody 12F1 to characterize the differentiation antigen VLA-2

A monoclonal antibody, 12F1, has been produced that specifically immunoprecipitates the human cell surface structure VLA-2 from platelets and long-term activated T cells, as well as from fibroblast and neuroblastoma cell lines. Cross-linking studies indicate that the VLA-2 structure exists on the cell surface as a 165,000 Mr heavy chain (alpha 2) in noncovalent 1:1 association with a 130,000 Mr light chain (beta). The monoclonal antibody A-1A5, which reacts with the beta subunit common to all VLA structures, was able to completely preclear VLA-2, indicating that all of the alpha 2 subunit was associated with VLA beta-chain. The specificity of 12F1 for VLA-2 allowed independent immunoprecipitation and flow cytometry analysis of this alpha 2 beta structure separate from any other VLA structures that may have been present such as VLA-1 or free beta-subunit. Subunit dissociation studies were used to demonstrate that 12F1 recognizes an epitope on the alpha 2 chain on VLA-2, which is consistent with the 12F1 specificity for VLA-2 alone among the VLA proteins. Analysis of activated T cells indicated that VLA-2, like VLA-1, is another "very late" appearing T cell activation antigen that arises concurrently with VLA-1 starting at day 7 and increasing through 2 wk. VLA-2 was found on many of the same cells as VLA-1 (inactivated T cells, T cell leukemia cells, fibroblasts, SK-N-SH neuroblastoma cells), but VLA-1 and VLA-2 can be expressed independently, because VLA-2 was also present on VLA-1-negative cells such as HSB and platelets, and VLA-1 was present on VLA-2-negative C8215 cells.

Use of the monoclonal antibody 12F1 to characterize the differentiation antigen VLA-2

A monoclonal antibody, 12F1, has been produced that specifically immunoprecipitates the human cell surface structure VLA-2 from platelets and long-term activated T cells, as well as from fibroblast and neuroblastoma cell lines. Cross-linking studies indicate that the VLA-2 structure exists on the cell surface as a 165,000 Mr heavy chain (alpha 2) in noncovalent 1:1 association with a 130,000 Mr light chain (beta). The monoclonal antibody A-1A5, which reacts with the beta subunit common to all VLA structures, was able to completely preclear VLA-2, indicating that all of the alpha 2 subunit was associated with VLA beta-chain. The specificity of 12F1 for VLA-2 allowed independent immunoprecipitation and flow cytometry analysis of this alpha 2 beta structure separate from any other VLA structures that may have been present such as VLA-1 or free beta-subunit. Subunit dissociation studies were used to demonstrate that 12F1 recognizes an epitope on the alpha 2 chain on VLA-2, which is consistent with the 12F1 specificity for VLA-2 alone among the VLA proteins. Analysis of activated T cells indicated that VLA-2, like VLA-1, is another "very late" appearing T cell activation antigen that arises concurrently with VLA-1 starting at day 7 and increasing through 2 wk. VLA-2 was found on many of the same cells as VLA-1 (inactivated T cells, T cell leukemia cells, fibroblasts, SK-N-SH neuroblastoma cells), but VLA-1 and VLA-2 can be expressed independently, because VLA-2 was also present on VLA-1-negative cells such as HSB and platelets, and VLA-1 was present on VLA-2-negative C8215 cells.

Detection of prey by captive Ningaui ridei and Sminthopsis griseoventer (Marsupialia: Dasyuridae)

The role of olfaction, vision and hearing in prey detection was investigated in Sminthopsis griseoventer and Ningaui ridei. Prey were presented so that they could be detected by one or a combination of these senses. When prey was presented so that only one sense could be used, prey were detected only by olfaction. When prey were presented so that two or all senses could be used, prey detection was fastest when all three senses were used and faster when hearing was used in combination with olfaction than when vision was used in combination with olfaction. It is suggested that hearing and vision may direct prey investigation by olfaction, and so speed location of prey.

Comparison of the diets of the feathertail glider, Acrobates pygmaeus, and the eastern pygmy-possum, Cercartetus nanus (Marsupialia: Burramyidae) in sympatry

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Polymorphic phase behavior of platelet-activating factor

Vibrational Raman and 31P NMR spectroscopic experiments have been performed as a function of temperature on aqueous dispersions of 1-0-octadecyl-2-acetoyl-sn-glycero-3-phosphocholine, a chemically synthesized platelet-activating factor. In the temperature range of -7 to 30 degrees C, the C(18)/PAF-H2O system is shown, upon heating, to undergo two thermal phase transitions centered at 9.2 degrees and 18.4 degrees C. The low temperature transition, attributed to the interdigitated lamellar gel (II)----gel (I) phase transition, is characterized by the breakdown of large lamellar organizations into small, but aggregated, bilayer vesicles. The high-temperature transition corresponds to the interdigitated lamellar gel (I)----micellar transition. The molecular ordering and packing structure of C(18)/PAF in the two lamellar phases and phase transition regions are described. It appears that the interdigitated lamellar gel (I) phase is unique for C(18)/PAF dispersions when compared with the behavior of other chemically closely related phospholipids in excess water.

Vaccinia virus vectors utilizing the beta-galactosidase assay for rapid selection of recombinant viruses and measurement of gene expression

Plasmids were constructed fusing vaccinia transcriptional regulatory sequences (promoters) to the lacZ gene of Escherichia coli. These recombinant plasmids were used to compare relative promoter strengths in transient expression assays and to construct recombinant vaccinia viruses producing beta-galactosidase (beta Gal). Viruses synthesizing beta Gal were determined by utilizing the chromogenic substrate, 5-bromo-4-chloro-3-indoyl-beta-D-galactoside to form blue plaques. A recombinant virus producing beta Gal was then used to select a second recombinant virus. This was accomplished via in vivo recombination replacing the lacZ gene with a sequence coding for the gp85 protein of Friend murine leukemia virus. The recombinant virus was selected by its inability to form blue plaques under appropriate conditions.

Two types of hydrocarbon chain interdigitation in sphingomyelin bilayers

Vibrational Raman spectroscopic experiments have been performed as a function of temperature on aqueous dispersions of synthetic DL-erythro-N-lignoceroylsphingosylphosphocholine [C(24):SPM], a racemic mixture of two highly asymmetric hydrocarbon chain length sphingomyelins. Raman spectral peak-height intensity ratios of vibrational transitions in the C-H stretching-mode region show that the C(24):SPM-H2O system undergoes two thermal phase transitions centered at 48.5 and 54.5 degrees C. Vibrational data for fully hydrated C(24):SPM are compared to those of highly asymmetric phosphatidylcholine dispersions. The Raman data are consistent with the plausible model that the lower temperature transition can be ascribed to the conversion of a mixed interdigitated gel state (gel II) to a partially interdigitated gel state (gel I) and that the higher temperature transition corresponds to a gel I----liquid-crystalline phase transition. The observation of a mixed interdigitated gel state (gel II) at temperatures below 48.5 degrees C implies that biological membranes may have lipid domains in which some of the lipid hydrocarbon chains penetrate completely across the entire hydrocarbon width of the lipid bilayer.

Acyl chain interdigitation in saturated mixed-chain phosphatidylcholine bilayer dispersions

The molecular packing of various fully hydrated mixed-chain phosphatidylcholines was studied by X-ray diffraction and electron microscopy. All of the mixed-chain phosphatidylcholines under study were shown to adopt a lamellar or bilayer form in aqueous media. The bilayer thickness of these mixed-chain phosphatidylcholines was determined from the lamellar repeat distance in the small-anglé X-ray diffraction region by controlled swelling experiments. At T greater than Tm, the bilayer thickness of C(18):C(12)PC and C(18):C-(10)PC is found to be comparable to that of C(14):C(14)PC. In contrast, the bilayer thickness of these highly asymmetric phosphatidylcholines is considerably less than that of the symmetric C(14):C(14)PC at temperatures below Tm. Moreover, the wide-angle X-ray diffraction patterns taken at T less than Tm consist of at least two sharp reflections at 4.2 and 4.6 A. These X-ray diffraction data suggest that these highly asymmetric mixed-chain phospholipids, in excess water, form mixed interdigitated bilayers in the gel state and that the acyl chain packing in the gel-state bilayer is not hexagonal. The freeze-fracture planes of these mixed-chain phosphatidylcholines are discontinuous at T less than Tm, supporting the conclusion drawn from X-ray diffraction data that these highly asymmetric phosphatidylcholines form interdigitated bilayers at temperatures below Tm. The molecular packing of fully hydrated C(18):C(14)PCs in bilayers is distinctively different from that of C(18):C(10)PCs or C(18):C(10)PCs.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of liposomal size on the calorimetric behavior of mixed-chain phosphatidylcholine bilayer dispersions

The effect of liposomal size on the endothermic transition profiles of the saturated mixed-chain phosphatidylcholines 1-stearoyl-2-myristoyl-sn-glycero-3-phosphocholine and 1-stearoyl-2-caproyl-sn-glycero-3-phosphocholine has been investigated. Liposomal bilayer dispersions of progressively smaller average diameter were prepared by extrusion of coarse multilamellar preparations of these lipids through polycarbonate membrane filters of decreasing pore size from 3-to 0.2-micrometers diameter. These samples were then investigated by high-sensitivity differential scanning calorimetry and negative-strain electron microscopy. It was found that coarse dispersions of the above lipids are composed of liposomes whose average diameter is considerably smaller than that typically associated with multilamellar liposomes of synthetic phosphatidylcholines. This fact, coupled with an analysis of the size dependence of the transition cooperativity, leads to the conclusion that the small size of the liposomes limits the transition cooperativity in coarse dispersions of these mixed-chain phosphatidylcholines. Thus, the broad and highly asymmetric transition profiles that have been observed in previous studies of these phosphatidylcholines are postulated to arise largely from this size dependence, rather than from characteristic packing properties of the phospholipid acyl chains as has been previously suggested.

Senile dementia and hydrocephalus due to carotid dolichoectasia

A 65-year-old hypertensive man presented with progressive dementia, and bilateral lower limb weakness. Computerised tomography revealed carotid arterial dolichoectasia and hydrocephalus. This uncommon entity may constitute another form of surgically treatable dementia in the elderly.

Partial characterization of six chlorophyll a-protein complexes isolated from a blue-green alga by a nondetergent method

The chlorophyll a-protein complexes of a blue-green alga, Phormidium luridum, are resolved in the absence of detergent, by the combination of a Sepharose 4B column and sucrose density gradient centrifugation, into six chlorophyll a-containing zones. These six complexes are termed here as F15, F25, F35, F40, F60, and F65, according to their appearance in the sucrose density gradient after centrifugation. The absorption spectra of these six isolated complexes are reported, as well as the fluorescence emission spectra at room temperature and liquid-nitrogen temperature. The F60 complex was enriched in Photosystem I, while the F35 and F40 complexes contained both Photosystem I and II. The F60 complex is the predominant band and accounts for about 49% of the total chlorophyll a of the cells. The extinction coefficient of this complex is determined to be 68.7 mM-1 cm-1 at 680 nm in 50 mM tris(hydroxymethyl)amino methane buffer at pH 8.0. In addition, the effect of the detergent, sodium dodecyl sulfate, on these spectra are also reported for comparison. The chemically induced difference spectra of F35, F40, and F60 complexes also indicate the presence of the reaction center, P700, of Photosystem I. These three complexes have been shown to contain P700 in a ratio of approximately one reaction center molecule per 100 light-harvesting chlorophyll molecules. The simple exposure of the F60 fraction to sodium dodecyl sulfate results in an "apparent" enhancement of the P700 to chlorophyll ratio to one P700 per 51 light harvesting chlorophyll. Room temperature electron spin resonance measurements of photooxidized F60 are consistent with the presence of P700 and with the chlorophyll/P700 ratio observed by chemical assay. The amino acid compositions of F60 and F65 complexes are studied. Gel electrophoresis patterns of these six isolated complexes are presented and are significantly different from those reported for detergent-treated chlorophyll-protein complexes.

An ultracentrifuge study of C-phycocyanin aggregation

The molecular weight of C-phycocyanin has been determined as a function of protein concentration in a sodium acetate buffer solution of pH 4.8 at 21.2 degrees C by the Yphantis method. The higher aggregate, the dodecamer (19 S), is first removed by dissociation simply by dialysis against pH 3.9 acetate buffer solution. The molecular weight data are best interpreted by the simultaneous presence of monomers, trimers, and hexamers. Assuming a monomer K13 in equilibrium trimer K36 in equilibrium hexamer equilibrium system, the equilibrium constants have been calculated, and the values are K13 = 1.4 x 10(12) (L/mol)2 and K36 = 6.1 x 10(5) L/mol. The corresponding free energies for each step have been calculated to be -16.3 kcal/mol (delta G degrees 13) and -7.76 kcal/mol (delta G degrees 36). With these values of K13 and K36, the weight-average molecular weight as a function of concentration is calculated. Satisfactory agreement is obtained between the calculated curve and the experimental data. Sedimentation velocity studies performed with a band-forming centerpiece, on the same protein solutions used for the sedimentation equilibrium studies, confirm the presence of three species: monomers, trimers, and hexamers.

Calorimetric investigations of saturated mixed-chain phosphatidylcholine bilayer dispersions

A series of saturated mixed-chain phosphatidylcholines were prepared whose sn-2 acyl chains are two, four, six, and eight carbon atoms shorter than the sn-1 acyl chain. The calorimetric behavior of multilamellar bilayers of these phosphatidylcholines in excess water is investigated. The phosphatidylcholines display cooperative phase transitions which are dependent upon both the difference in chain length and the position of the acyl chains on the glycerol backbone of the phospholipid. A model is proposed which suggests that the thermotropic behavior of the mixed-chain phosphatidylcholines results from progressively greater interdigitation of the acyl chains of the phospholipid across the bilayer center, in the gel state, as the chain-length difference is increased beyond a minimum value. The disruptive effect of the terminal methyl groups of the fatty acyl chains upon the bilayer packing stability is also stressed. Dispersions of some of the mixed-chain phosphatidylcholines display transition endotherms which appear to be composites of two or more individual transition peaks. The dependence of this behavior on the thermal history of the dispersions is investigated. It is proposed that these peaks arise from the ability of the phosphatidylcholines' acyl chains to pack in more than one interdigitated conformation in the gel state.

Modification and identification of glutamate residues at the arginine-recognition site in the catalytic subunit of adenosine 3' :5'-cyclic monophosphate-dependent protein kinase of rabbit skeletal muscle

It has been proposed that the active centre of cyclic AMP-dependent protein kinase contains an arginine-recognition site, which is considered to be essential for the function of the catalytic subunit of the kinase [Matsuo, Huang & Huang (1978) Biochem. J.173, 441-447]. The catalytic subunit can be inactivated by 3-(3-dimethylaminopropyl)-1-ethylcarbodi-imide and glycine ethyl ester at pH6.5. The enzyme can be protected from inactivation by preincubation with histone, a protein substrate of the enzyme. On the other hand, ATP, which also serves as a protein kinase substrate, does not afford protection. Polyarginine, a competitive inhibitor of protein kinase, which is known from kinetic studies to interact specifically with the arginine-recognition site, partially protects the catalytic subunit from inactivation by 3-(3-dimethylaminopropyl)-1-ethylcarbodi-imide. These results lead to the conclusion that the site of modification by carbodi-imide/glycine ethyl ester is most likely located at the arginine-recognition site of the active centre. A value of 1.7+/-0.2 (mean+/-s.d.) mol of carboxy groups per mol of catalytic subunit has been obtained for the number of essential carboxy groups for the function of protein kinase; a complete chemical modification of these essential carboxy groups results in total loss of catalytic activity. Finally, we have identified the essential carboxy group in the catalytic subunit of cyclic AMP-dependent protein kinase as being derived from glutamate residues. This is achieved by a three-step procedure involving an extensive proteolytic digestion of the [1-(14)C]glycine ethyl ester-modified enzyme and two successive high-voltage electrophoreses of the hydrolysate. It is concluded that 1.7mol of glutamyl carboxy groups per mol of catalytic subunit may be considered a component of the arginine-recognition site in the active centre of cyclic AMP-dependent protein kinase.

Kinetic studies on the dissociation of adenosine cyclic 3',5'-monophosphate from the regulatory subunit of protein kinase from rabbit skeletal muscle

The exchange rate of unlabeled adenosine 3',5'-monophosphate (cAMP) with labeled [3H]cAMP in the dimeric regulatory subunit-cAMP complex of cAMP-dependent protein kinase, type I, purified from rabbit skeletal muscle is described by using the equilibrium isotope exchange technique. Results indicate that the rate of exchange carried out in the absence of the catalytic subunit (C) is rather slow with a half-life of approximately 870 s. This slow exchange rate is not affected by the presence of MgATP (50 microM). However, when both MgATP (50 microM) and C (1-13 NM) are present, the rate of isotope exchange is observed to increase markedly. Furthermore, less than stoichiometric amounts of C are required for the increase in the rate of cAMP exchange, indicating that the effect of C on the rate enhancement is a catalytic process. These results indicate that in the presence of MgATP, a ternary complex between C and regulatory subunit-cAMP complex must be formed, and a dynamic equilibrium between the eternary complex and its dissociable species must be reached within seconds. On the basis of our kinetic data, it is proposed that the formation of this ternary complex intermediate allows the rapid activation or the inactivation of cAMP-dependent protein kinase following changes in the cellular cAMP levels.

Design of an artificial skin. II. Control of chemical composition

Detailed methodology is described for the reproducible preparation of collagen--glycosaminoglycan (GAG) membranes with known chemical composition. These membranes have been used to cover satisfactorily large experimental full-thickness skin wounds in guinea pigs over the past few years. Such membranes have effectively protected these wounds from infection and fluid loss for over 25 days without rejection and without requiring change or other invasive manipulation. When appropriately designed for the purpose, the membranes have also strongly retarded wound contraction and have become replaced by newly synthesized, stable connective tissue. In our work, purified, fully native collagen from two mammalian sources is precipitated from acid dispersion by addition of chondroitin 6-sulfate. The relative amount of GAG in the coprecipitate varies with the amount of GAG added and with the pH. Since coprecipitated GAG is generally eluted from collagen fibers by physiological fluids, control of the chemical composition of membranes is arrived at by crosslinking the collagen--GAG ionic complex with glutaraldehyde, or, alternately, by use of high-temperature vacuum dehydration. Appropriate use of the crosslinking treatment allows separate study of changes in membrane composition due to elution of GAG by extracellular fluid in animal studies from changes in composition due to enzymatic degradation of the grafted or implanted membrane in these studies. Exhaustive in vitro elution studies extending up to 20 days showed that these crosslinking treatments insolubilize in an apparently permanent manner a fraction of the ionically complexed GAG, although it could not be directly confirmed that glutaraldehyde treatment covalently crosslinks GAG to collagen. By contrast, the available evidence suggests strongly that high-temperature vacuum dehydration leads to formation of chemical bonds between collagen and GAG. Procedures are described for control of insolubilized and "free" GAG in these membranes as well as for control of the molecular weight between crosslinks (Mc). The insolubilized GAG can be controlled in the range 0.5--10 wt. % while "free" GAG can be independently controlled up to at least 25 wt. %; Mc can be controlled in the range 2500--40,000. Studies by infrared spectroscopy have shown that treatment of collagen--GAG membranes by glutaraldehyde or under high-temperature vacuum does not alter the configuration of the collagen triple helix in the membranes. Neither do these treatments modify the native banding pattern of collagen as viewed by electron microscopy. Collagen--GAG membranes appear to be useful as chemically well-characterized, solid macromolecular probes of biomaterial--tissue interactions.

A method for the enzymatic synthesis and purification of [alpha-32P] nucleoside triphosphates

A simplified method is described for the enzymatic synthesis and purification of [alpha-32P]ribo- and deoxyribonucleoside triphosphates. The products are obtained at greater than 97% radiochemical purity with yields of 50--70% (relative to 32Pi) by a two-step elution from DEAE-Sephadex. All reactions are done in one vessel as there is no need for intermediate product purifications. This method is therefore suitable for the synthesis of these radioactive compounds on a relatively large scale. The sequential steps of the method involve first the synthesis of [gamma-32P]ATP and the subsequent phosphorylation of nucleoside 3' monophosphate with T4 polynucleotide kinase to yield nucleoside 3', [5'-32P]diphosphate. Hexokinase is used after the T4 reaction to remove any remaining [gamma-32P]ATP. Nucleoside 3',[5'-32P]diphosphate is treated with nuclease P-1 to produce the nucleoside [5'-32P]monophosphate which is phosphorylated to the [alpha-32P]nucleoside triphosphate with pyruvate kinase and nucleoside monophosphate kinase. Adenosine triphosphate used as the phosphate donor for [alpha-32P]deoxynucleoside triphosphate syntheses is readily removed in a second purification step involving affinity chromatography on boronate-polyacrylamide. [alpha-32P]Ribonucleoside triphosphates can be similarly purified when deoxyadenosine triphosphate is used as the phosphate donor.

Geometric packing constraints in egg phosphatidylcholine vesicles

This investigation presents a quantitative analysis of the asymmetric transmembrane lipid packing geometry in egg phosphatidylcholine vesicles. The analysis uses hydrodynamic and nuclear magnetic resonance data obtained for homogeneous egg phosphatidylcholine vesicles and demonstrates that the average area per lipid head group and effective length of the lipid are greater on the outer monolayer than on the inner monolayer of the egg phosphatidylcholine vesicle. Results also indicate that the bilayer of the egg phosphatidylcholine vesicles has an asymmetrical interface through its center.

[Short-term hemodialyses using large surface dialysers]

Twice a wekk the dialysis was carried out for four hours, since a lack of personnel and institutions excluded a therapy repeated three times a week. The patients should optimally be treated for three hours three times a week. Patients dialysed by this means show favourable values of blood pressure under a minimum antihypertensive medication. They are less anaemic and in most cases more active than those patients who are dialysed twice a week. The use of the short time dialysis with capillary kidneys of a large surface increased the number of the patients treated and improved the functional capacity of the chronic dialysis programme.

Phospholipid head-group conformations; intermolecular interactions and cholesterol effects

The predominant orientation of the phosphorylcholine polar head group in phosphatidylcholine and sphingomyelin bilayers and cholesterol perturbations of that orientation have been identified by exploiting the 31P (1H) nuclear Overhauser effect (NOE) in the 31P NMR spectra of phospholipid bilayers. In pure egg phosphatidylcholine bilayers, a NOE of 40% is observed. The magnitude of the NOE has been measured as a function of continuous-wave proton-decoupler frequency in order to identify the proton source of the NOE. In pure egg phosphatidylcholine bilayers, the maximum NOE occurs at the N-methyl proton resonance position of the choline moiety. In a modified phosphatidylcholine in which all the N-methyl protons were replaced by deuterium, the NOE arose from methylene protons next to the phosphate. In mixed systems of phosphatidylcholine and phosphatidylethanolamine, and phosphatidylcholine and diphosphatidylglycerol, both phospholipid resonances attained maximum NOE at the position of the N-methyl proton resonance of phosphatidylcholine. An analogous result was obtained with pure sphingomyelin. These results are explained by orienting the phosphorylcholine portion of the molecule parallel to the surface of the bilayer so that the positively charged N-methyl moiety is located close to the negatively charged phosphate on a neighboring phospholipid in an intermolecular interaction. Addition of cholesterol is shown to disrupt the intermolecular interaction in phosphatidylcholine bilayers.

Configurations of fatty acyl chains in egg phosphatidylcholine-cholesterol mixed bilayers

Based on the structural properties of cholesterol and egg phosphatidylcholine, and on the assumption that the van der Waals' type attactive interaction between the steroid nucleus and the fatty acyl chains provides a stabilizing force for the cholesterol-egg phosphatidylcholine complex, some specific orientation and configurations of the fatty acyl chains around the steroid nucleus in the interacting system are proposed in terms of an optimal packing. The proposed model suggests thathe saturated chains are largely facing the flattened (alpha) surface of the steroid nucleus of cholesterol, while the unsaturated chains can interact with both the alpha and beta surfaces of the steroid nucleus. It is also suggested that the angular methyl groups on the beta surface of the steroid nucleus lock the unsaturated fatty acyl chain in a relatively immobile configuration. Experimental evidence which provides support for the proposed stereochemical model is presented.