Neutralization of thoron progeny in gases

This paper reports charge neutralization phenomena of 212Pb particles in nitrogen or oxygen atmospheres with trace amounts of other gases. Newly produced thoron or radon progeny are positively charged, stable molecular clusters that are subsequently neutralized by several mechanisms. The charged clusters have a smaller diffusion coefficient than neutral clusters of the same size due to the interaction of the charge with the surrounding gas molecules. In this study, we have found that the diffusion coefficients of 212Pb in O2, N2, NH3/O2, NH3/N2, and C6H12/N2 (IPs between 15.58 and 9.8 eV) ranged between 0.015 and 0.030 cm2 s-1. In the case of C6H12/O2, NO2/O2, NO/O2, and dimethylamine/O2 (ionization potential between 9.8 and 8.23 eV), the diffusion coefficients have increased to between 0.046 and 0.69 cm2 s-1. These results are consistent with previous results of 218Po, indicating that charged progeny are neutralized by electron transfer from a gas molecule with a lower ionization potential than lead oxide. We estimate the ionization potential of lead oxide to range between 9.8 and 10.2 eV. 212Pb was also neutralized by an electron scavenging mechanism in NO2/nitrogen.

Theory of image formation using the Talbot effect

The information inside each subcell of a two-dimensional periodic object is replicated throughout all the subcells of the unit cell at certain planes. An explicit expression describing the relative phase relationship among the replicated information is derived. From this expression, the wave amplitude at all the subcells caused by the interaction among the information coming from different subcells in the original object is obtained. A computer simulation of gray-level image synthesis using binary substructures and image differentiation is also given.

Intercomparison of activity size distributions of thoron progeny by alpha- and gamma-counting methods

It is difficult to calibrate sampling devices using radon or thoron progeny or particles measuring 1-4 nm; therefore, an interlaboratory comparison is important to verify the performance of graded diffusion batteries for the activity size distributions of the "unattached" progeny. This paper describes the results of an interlaboratory comparison of 220Rn progeny size distributions using graded diffusion batteries by alpha- and gamma-counting methods with different data inversion schemes. Graded diffusion batteries designed at the Inhalation Toxicology Research Institute and at the Environmental Measurement Laboratory were used in the study. Screens and backup filters from the Environmental Measurement Laboratory-graded diffusion batteries were counted simultaneously in alpha counters for total alpha activities, and those of the Inhalation Toxicology Research Institute-graded diffusion batteries were counted in a gamma detector for gamma activities from 212Pb. Because of the different counting methods and data analysis procedures used, this interlaboratory study of 220Rn progeny allows a more rigorous way of testing instrument performance. 212Pb particles generated in well-controlled environments of oxygen, nitrogen, or oxygen with 1 ppm of nitrogen oxide were measured. In general, good agreement in activity size distributions was obtained from these two methods. Some differences observed in individual size spectra were attributable to the data inversion programs used in each laboratory. When the data were analyzed by the same computer program, most differences disappeared.

Self-assembly and calcium-binding sites in laminin. A three-arm interaction model

Laminin, a four-arm glycoprotein, polymerizes in vitro into networks similar to those found in basement membranes. We have dissected this calcium-dependent assembly by analyzing proteolytic fragment binding using equilibrium gel filtration, ultracentrifugation, and electron microscopy. The cathepsin G fragment C1-4 (three short arms) was found to aggregate with a critical concentration similar to that for laminin. Like laminin polymerization, this assembly was inhibited by the smaller elastase short arm fragments E4 (B1 domains VI and V) and E1' (A-B2 short arm complex). Fragment E4 bound directly to E1' in a calcium-dependent manner (KD = 1.4 microM). In contrast, homologous self-interactions of short arm fragments and all interactions of long arm fragments were considerably weaker or nonexistent. While electron micrographs of E1' or E4 alone contained mostly monomers, those of E1'/E4 mixtures contained dimers and oligomers with E1' dimers connected to each other through their A and B2 arms, often with visible E4 molecules at their junctions. 45Ca2+ bound principally to fragment E1' with localization to the end of the B2 chain. These data support a model in which polymerization requires the interaction of all three ligands, one from each short arm, with calcium activating assembly by binding to the B2 short arm.

In vitro isolation and identification of human immunodeficiency virus (HIV) variants with reduced sensitivity to C-2 symmetrical inhibitors of HIV type 1 protease

Protease inhibitors are another class of compounds for treatment of human immunodeficiency virus (HIV)-caused disease. The emergence of resistance to the current anti-HIV drugs makes the determination of potential resistance to protease inhibitors imperative. Here we describe the isolation of an HIV type 1 (HIV-1) resistant to an HIV-protease inhibitor. Serial passage of HIV-1 (strain RF) in the presence of the inhibitor, [2-pyridylacetylisoleucylphenylalanyl-psi (CHOH)]2 (P9941), failed to yield a stock of virus with a resistance phenotype. However, variants of the virus with 6- to 8-fold reduced sensitivity to P9941 were selected by using a combination of plaque assay and endpoint titration. Genetic analysis and computer modeling of the variant proteases revealed a single change in the codon for amino acid 82 (Val-->Ala), which resulted in a protease with lower affinity and reduced sensitivity to this inhibitor and certain, but not all, related inhibitors.

Isolation of astaxanthin over-producing mutants of Phaffia rhodozyma and their fermentation kinetics

Phaffia rodozyma CCRC-21346, CBS-6938, and CBS-5908 were treated with mutagenic agent NTG (N-methyl-N'-nitro-N-nitrosoguanidine) several times, then they were plated onto yeast-malt agar containing beta-ionone as a selective medium. Several isolates had increased astaxanthin content compared with the parental natural isolates. NCHU-FS301, one of the NTG treated strains, produced considerably more astaxanthin (1515.63 micrograms/g yeast) than the parent CBS-6938 (565.08 micrograms/g yeast). In studying the effects of carbon sources on the red pigment formation, it was found that glucose supported the highest total astaxanthin production (7809.3 micrograms/l). Yeast extract was the best nitrogen source in supporting the highest total astaxanthin formation (8637.5 micrograms/l). Beef extract, yeast extract, and potassium nitrate added in an equal ratio as a nitrogen source supported more pigment formation (8052.6 micrograms/l) than the rest of the mixture tested. Using kinetic parameters of specific growth rate (mu) and specific astaxanthin productivity (qp) to judge the association between growth behavior and product formation, the NCHU-FS301 showed more positive growth-associated fermentation type than the parent strain. These astaxanthin-overproducing mutants could be useful for the aquacultural industry in providing a natural source of astaxanthin.

The effect of exposure pattern on the accumulation of particles and the response of the lung to inhaled particles

We hypothesized that a rapid rate of delivery of particles to the lung would overwhelm the normal clearance mechanisms of the lung and result in a higher lung burden of particles and a greater inflammatory response than a slower rate of particle delivery. F344/N rats were exposed over a 12-week period to the same weekly concentration times time product of carbon black (CB) particles, but at three different exposure rates: 3.5 mg/m3, 16 hr/day, 7 days/week; 13 mg/m3, 6 hr/day, 5 days/week; or 98 mg/m3, 4 hr/day, 1 day/week. The intermediate exposure rate was chosen to mimic an occupational work week and to give an 8-hr, time-weighted average exposure equal to the threshold limit value (TLV) for nuisance dusts of the American College of Governmental Industrial Hygienists (10 mg/m3). Pure CB has a lower TLV, 3.5 mg/m3, than nuisance dusts, but this is based on avoidance of excessive dirtiness in the workplace, not on the toxicity of CB. Lung burdens of CB were measured after 3, 6, 9, and 12 weeks of exposure and at 4, 8, 12, 16, and 24 weeks after the exposure ended. The inflammatory response was quantified by analysis of bronchoalveolar lavage fluid (BALF) after 6 and 12 weeks of exposure and at 1, 12, and 24 weeks after exposure. The histopathology of the lung was evaluated at the end of the exposure and at 24 weeks after the exposure. Acquired lung burdens were between 3 and 4 mg/lung at the end of the exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Laminin forms an independent network in basement membranes

Laminin self-assembles in vitro into a polymer by a reversible, entropy-driven and calcium-facilitated process dependent upon the participation of the short arm globular domains. We now find that this polymer is required for the structural integrity of the collagen-free basement membrane of cultured embryonal carcinoma cells (ECC) and for the supramolecular organization and anchorage of laminin in the collagen-rich basement membrane of the Engelbreth-Holm-Swarm tumor (EHS). First, low temperature and EDTA induced the dissolution of ECC basement membranes and released approximately 80% of total laminin from the EHS basement membrane. Second, laminin elastase fragments (E4 and E1') possessing the short arm globules of the B1, B2, and A chains selectively acted as competitive ligands that dissolved ECC basement membranes and displaced laminin from the EHS basement membrane into solution. The fraction of laminin released increased as a function of ligand concentration, approaching the level of the EDTA-reversible pool. The smaller (approximately 20%) residual pool of EHS laminin, in contrast, could only be effectively displaced by E1' and E4 if the collagenous network was first degraded with bacterial collagenase. The supramolecular architecture of freeze-etched and platinum/carbon replicated reconstituted laminin gel polymer, ECC, and collagenase-treated EHS basement membranes were compared and found to be similar, further supporting the biochemical data. We conclude that laminin forms a network independent of that of type IV collagen in basement membranes. Furthermore, in the EHS basement membrane four-fifths of laminin is anchored strictly through noncovalent bonds between laminin monomers while one-fifth is anchored through a combination of these bonds and laminin-collagen bridges.

Synthesis and in vitro evaluation of [Leu13]porcine motilin fragments

Several peptide fragments representing N-terminal, C-terminal, and internal sequences of [Leu13]porcine motilin ([Leu13]pMOT) were synthesized using Fmoc solid phase methodology. Peptides were assayed for motilin receptor binding activity in a rabbit antrum smooth muscle preparation and for stimulation of contractile activity in segments of rabbit duodenum. In vitro activity was directly correlated with motilin receptor binding affinity for all [Leu13]pMOT fragments examined. N-Terminal fragments of just over half the length of the native peptide are nearly equipotent as full-length motilin. These results suggest that the N-terminal segment, together with residues from the mid-portion of the molecule, constitutes the bioactive portion of pMOT. The C-terminal segment, in contrast, contributes little to receptor binding affinity or in vitro activity.

Human immunodeficiency virus type 1 and type 2 protease monomers are functionally interchangeable in the dimeric enzymes

Human immunodeficiency virus type 1 (HIV-1) and HIV-2 proteases are dimers of identical subunits. We made a construct for the expression of recombinant one-chain HIV-2 protease dimer, which, like the previously described one-chain HIV-1 protease dimer, is fully active. The constructs for the one-chain dimers of HIV-1 and HIV-2 proteases were modified to produce hybrid one-chain dimers consisting of both HIV-1 and HIV-2 protease monomers. Although the monomers share only 47.5% sequence identity, the hybrid one-chain dimers are fully active, suggesting that the folding of both HIV-1 and HIV-2 protease monomers is functionally similar.

Molecular characterization of HIV-2 (ROD) protease following PCR cloning from virus infected H9 cells

A 450 nucleotide sequence corresponding to the nucleotides 1931-2380 of the viral genome (8) was amplified by polymerase chain reaction (PCR) using template DNA prepared from HIV-2 (ROD) infected H9 cells. The sequence codes for HIV-2 protease and its N-terminal flanking peptide. An identical DNA sequence was obtained from three independent PCR amplifications, which differs from the published sequence of HIV-2 (ROD) in 7 nucleotides scattered throughout the region of the cloned DNA. The cloned DNA was expressed in E. coli cells and resulted in the synthesis of a correctly processed HIV-2 protease, which is enzymatically active. Therefore, none of the seven nucleotide changes, which resulted in two amino acid substitutions, affect the autoproteolytic or trans-cleaving activities of the HIV-2 protease.

In vitro activity of silicon carbide whiskers in comparison to other industrial fibers using four cell culture systems

Silicon carbide whiskers (SiCW) and continuous glass filaments are important components of composite materials having potentially widespread use in the automotive, aerospace, and power generation industries. We determined the in vitro activity of three well-characterized samples of silicon carbide whiskers and a continuous glass filament sample in four different cellular assays and compared this to the activities of UICC crocidolite, JM Code 100 glass microfiber, and erionite in the same assay systems. The SiCW had a diameter range of 0.32-0.75 microns and a length range of 4.5-20.1 microns. The SiCW was significantly toxic; on a mass basis, one SiCW sample was more toxic than crocidolite; however, JM Code 100 glass microfiber, which is not toxic in vivo (i.e., it does not cause fibrogenesis or carcinogenesis when inhaled), was also more toxic than crocidolite. The glass filament sample was the least cytotoxic of all the samples tested. On a fiber number basis, all three SiCW samples were more toxic than crocidolite. The results of our study showed that SiCW exhibits significant in vitro biological reactivity. Thus, despite the caution that must be exercised in extrpolating the results of in vitro studies to conclusions about in vivo health effects, SiCW should be considered toxic until further toxicological data are available.

Interferon-induced guanylate-binding proteins lack an N(T)KXD consensus motif and bind GMP in addition to GDP and GTP

The primary structures of interferon (IFN)-induced guanylate-binding proteins (GBPs) were deduced from cloned human and murine cDNAs. These proteins contained only two of the three sequence motifs typically found in GTP/GDP-binding proteins. The N(T)KXD motif, which is believed to confer guanine specificity in other nucleotide-binding proteins, was absent. Nevertheless, the IFN-induced GBPs exhibited a high degree of selectivity for binding to agarose-immobilized guanine nucleotides. An interesting feature of IFN-induced GBPs is that they strongly bound to GMP agarose in addition to GDP and GTP agaroses but failed to bind to ATP agarose and all other nucleotide agaroses tested. Both GTP and GMP, but not ATP, competed for binding of murine GBP-1 to agarose-immobilized GMP. The IFN-induced GBPs thus define a distinct novel family of proteins with GTP-binding activity. We further demonstrate that human and murine cells contain at least two genes encoding IFN-induced GBPs. The cloned murine cDNA codes for GBP-1, an IFN-induced protein previously shown to be absent from mice of Gbp-1b genotype.

Two-dimensional grating interferometric imaging of a near object by computed tomography

The Fourier coefficients of a near object can be obtained by analyzing the interference pattern in an achromatic grating interferometer. Using the projection slice theorem, the Fourier plane can be filled and the spatial irradiance distribution of a 2-D incoherent object can be reconstructed.

Higher-order analysis of four-beam cross grating interferometers

Both on- and off-axis four-beam interference patterns are analyzed using ray tracing. The cross gratinglike interference pattern is accompanied by an extra term which consists of two orthogonal two-beam interference patterns. When partially coherent light is used, the extra term generally degrades the contrast of the cross gratinglike pattern unless some special kinds of source are utilized. With gratings of high spatial frequencies, the amplitude of the extra term can become large compared with the desired term. Consequently, the localized cross gratinglike pattern is changed to be periodic in different directions.

In vivo deposition of ultrafine aerosols in the nasal airway of the rat

We studied the deposition of ultrafine aerosols, ranging in geometric diameter from 0.005 to 0.1 microns, in the nasal airway of Fischer-344/N rats, at inspiratory flow rates of 200, 300, 400, and 600 ml/min. Simultaneously, we measured the pressure drop across the rat nasal airway. The purpose was to determine whether the in vivo deposition of ultrafine aerosols in the rat nasal airway is the same as the deposition observed in rat nasal casts. At a flow rate of 400 ml/min, corresponding to the normal mean inspiratory flow rate of the rat, deposition efficiency increased from 6 to 58%, when the particle diameter decreased from 0.1 to 0.005 microns. For 0.005-microns-diameter particles, the deposition efficiency decreased from 68 to 52% when the flow rate was increased from 200 to 600 ml/min. These results agree well with those from previous experiments with nasal casts, which indicated that diffusion is the dominant mechanism for deposition of ultrafine aerosols. The pressure drop in the nasal airway of the rat increased almost linearly with flow rate, from 73 Pa at 200 ml/min to 247 Pa at 600 ml/min. These values are within the range of those obtained in previous experiments with nasal casts, although the pressure drop in casts increased as a power greater than 1 with flow rate. The results of our study support the use of nasal airway casts to estimate the in vivo deposition of ultrafine aerosols.

Stability and activity of human immunodeficiency virus protease: comparison of the natural dimer with a homologous, single-chain tethered dimer

A single-chain tethered dimer of human immunodeficiency virus protease (HIV-PR) was produced by expression of a synthetic gene in Escherichia coli. The tethered dimer, which consists of two 99-amino acid HIV-PR subunits linked together by a pentapeptide, was isolated from inclusion bodies and refolded as an active protease with enzymatic properties very similar to those of the natural dimer at pH 5.5. In addition to demonstrating that the tethered dimer is active, we have shown that the tethered dimer is more stable than the natural HIV-PR dimer at pH 7.0. This is attributed to dissociation of the natural HIV-PR dimer, for which a surprisingly high dissociation constant, 5 X 10(-8) M was measured. Furthermore, the tethered dimer offers an opportunity to produce asymmetric dimer mutants and thereby determine the effect of changes in one of the two subunits on protease activity. In one such mutant, a single active-site aspartic residue was changed to a glycine residue. This protein was inactive, consistent with a requirement for an aspartic residue from each subunit to constitute an active site of HIV-PR.

Deposition of ultrafine aerosols in rat nasal molds

To evaluate the health effects of air pollutants on the respiratory tract, it is critical to determine the regional deposition of inhaled aerosols. Information on deposition of larger particles (greater than 0.2 microns) in the nasal passages of laboratory animals is available; the deposition fraction increases with increasing particle size. However, little deposition information is available for ultrafine particles of less than 0.2 microns. Three clear, plastic molds (models) of the nasal passages of F344/N rats, prepared from metal replica casts were used in these studies. Total deposition of ultrafine aerosols in the casts was determined by using a unidirectional flow system. The pressure drops measured in the casts were a function of flow rate to the power of 1.4-1.6, indicating that flow through the nasal passages has nonlaminar components. Deposition data were obtained by using monodisperse sodium chloride aerosols with particle sizes ranging from 0.2 to 0.005 microns, at inspiratory and expiratory flow rates of 200 to 600 ml/min. Similar deposition data were obtained for two of the casts studied. Deposition efficiency was greatest for the smallest particles, and decreased with increasing particle size and flow rate. At an inspiratory flow rate of 400 ml/min, which is comparable to the mean respiratory flow of an adult male F344 rat with a respiratory minute volume of 200 ml, deposition efficiencies reached 40 and 70% for 0.01- and 0.005-microns particles, respectively. These studies demonstrated that turbulent diffusional deposition was the dominant mechanism for uptake of ultrafine particles by the nasal passages.

The immunotoxicity of three nickel compounds following 13-week inhalation exposure in the mouse

Groups of B6C3F1 mice were exposed to aerosols of nickel subsulfide (Ni3S2), nickel oxide (NiO), or nickel sulfate hexahydrate (NiSO4.6H2O) 6 hr/day, 5 days per week for 65 days to determine the immunotoxicity of these compounds. Exposure concentrations were 0.11, 0.45, and 1.8 mg Ni/m3 for Ni3S2, 0.47, 2.0, and 7.9 mg Ni/m3 for NiO; and 0.027, 0.11, and 0.45 mg Ni/m3 for NiSO4. Thymic weights were decreased only in mice exposed to 1.8 mg Ni/m3 Ni3S2. Increased numbers of lung-associated lymph nodes (LALN), but not spleen nucleated cells, were seen with all compounds. Nucleated cells in lavage samples were increased in mice exposed to the highest concentrations of NiSO4 and NiO and to 0.45 and 1.8 mg Ni/m3 Ni3S2. Increased antibody-forming cells (AFC) were seen in LALN of mice exposed to 2.0 and 7.9 mg Ni/m3 NiO and 1.8 mg Ni/m3 Ni3S2. Decreased AFC/10(6) spleen cells were observed in mice exposed to NiO, and decreased AFC/spleen were seen for mice exposed to 1.8 mg Ni/m3 Ni3S2. Only mice exposed to 1.8 mg Ni/m3 Ni3S2 had a decrease in mixed lymphocyte response. All concentrations of NiO resulted in decreases in alveolar macrophage phagocytic activity, as did 0.45 and 1.8 mg Ni/m3 Ni3S2. None of the nickel compounds affected the phagocytic activity of peritoneal macrophages. Only 1.8 mg Ni/m3 Ni3S2 caused a decrease in spleen natural killer cell activity. Results indicate that inhalation exposure of mice to nickel can result in varying effects on the immune system, depending on dose and physicochemical form of the nickel compound. These nickel-induced changes may contribute to significant immunodysfunction.

Effect of inhaled azodicarbonamide on F344/N rats and B6C3F1 mice with 2-week and 13-week inhalation exposures

Azodicarbonamide (ADA), a compound used in the baking and plastics industries, has been reported to cause pulmonary sensitization and dermatitis in people. Two-week repeated and 13-week subchronic inhalation exposures of F344/N rats and B6C3F1 mice to ADA were conducted to determine the toxicity of inhaled ADA. The mean air concentrations of ADA in the 2-week studies were 207, 102, 52, 9.4, or 2.0 mg/m3. No exposure-related mortality nor abnormal clinical signs were observed in rats or mice during or after exposure. The terminal body weights were slightly depressed in the highest exposure group. Liver weights were lower in male rats exposed to 200 mg ADA/m3. No significant lesions were noted on either gross or histologic evaluation of rats or mice. In the 13-week subchronic study, the mean air concentrations of ADA were 204, 100, or 50 mg/m3. No mortality or clinical signs related to exposure were observed. The terminal body weights of exposed rats were not significantly different from those of control rats but were significantly depressed in mice exposed to 100 or 200 mg ADA/m3. No histopathological lesions were noted in mice. Lung weights were increased and enlarged mediastinal and/or tracheobronchial lymph nodes were noted in rats exposed to 50 mg ADA/m3. No exposure-related lesions were observed microscopically in rats exposed to 100 or 200 mg ADA/m3. All rats in the 50 mg ADA/m3 exposure group only had lung lesions that consisted of perivascular cuffing with lymphocytes and a multifocal type II cell hyperplasia, suggesting a possible immune reaction to an antigen in the lung. Viral titers for rats exposed to 50 mg ADA/m3 were negative for Sendai virus and pneumonia virus of mice, which produce similar lesions. The possibility of an unknown viral antigen causing this lesion cannot be eliminated. Lung tissue from male rats was analyzed for ADA and biurea, the major metabolite of ADA. No ADA was detected. The amount of biurea in the lungs increased nonlinearly with increasing exposure concentration, suggesting that clearance was somewhat impaired with repeated exposures. However, even at the highest exposure concentration, this amount of biurea was less than 1% of the estimated total ADA deposited over the exposure period. In summary, ADA is rapidly cleared from the lungs, even when inhaled at concentrations up to 200 mg/m3. Exposure to ADA for up to 13 weeks did not appear to be toxic to rodents.

Influence of preexisting pulmonary emphysema on susceptibility of rats to inhaled diesel exhaust

The susceptibilities of normal rats and rats with preexisting pulmonary emphysema to chronically inhaled diesel exhaust were compared. Rats were exposed 7 h/day, 5 days/wk for 24 months to diesel exhaust at 3.5 mg soot/m3, or to clean air as controls. Emphysema was induced in one-half of the rats by intratracheal instillation of elastase 6 wk before exhaust exposure. Measurements included lung burdens of diesel soot, respiratory function, bronchoalveolar lavage, clearance of radiolabeled particles, pulmonary immune responses, lung collagen, excised lung weight and volume, histopathology, and mean linear intercept of terminal air spaces. Parameters indicated by analysis of variance to exhibit significant interactions between the influences of emphysema and exhaust were examined to determine if the effects were more than additive (indicating increased susceptibility). Although 14 of 63 parameters demonstrated emphysema-exhaust interactions, none indicated increased susceptibility. Less soot accumulated in lungs of emphysematous rats than in those of nonemphysematous rats, and the reduced accumulation had a sparing effect in the emphysematous rats. The results did not support the hypothesis that emphysematous lungs are more susceptible than are normal lungs to chronic exposure to high levels of diesel exhaust. The superimposition of effects of emphysema and exhaust, however, might still warrant special concern for heavy exposures of emphysematous subjects.

High-level synthesis of recombinant HIV-1 protease and the recovery of active enzyme from inclusion bodies

A complete chemical synthesis and assembly of genes for the production of human immunodeficiency virus type-I protease (HIV-PR) and its precursors are described. The T7 expression system was used to produce high levels of active HIV-PR and its precursors in Escherichia coli inclusion bodies. The gene encoding the open reading frames of HIV-PR was expressed in E. coli as a 10-kDa protein, while the genes encoding HIV-PR precursors were expressed as larger proteins, which were partially processed in E. coli to the 10-kDa form. These processing events are autoproteolytic, since a single-base mutation, changing the active-site aspartic acid to glycine, completely abolished the conversion. HIV-PR can be released with 8 M urea from washed cellular inclusion bodies, resulting in a preparation with few bacterial host proteins. After refolding, this preparation contains no nonspecific protease or peptidase activities. The recombinant HIV-PR isolated from inclusion bodies cleaves HIV-PR substrates specifically with a specific activity comparable to column-purified HIV-PR.

Heparin modulation of laminin polymerization

Previously, it has been shown that laminin will self-assemble by a two-step calcium-dependent process using end-domain interactions (Yurchenco, P. D., Tsi-library, E. C., Charonis, A. S., and Furthmayr, H. (1985) J. Biol. Chem. 260, 7636-7644). We now find that heparin, at low concentrations, modifies this polymerization by driving the equilibrium further toward aggregation, by producing a denser polymer, and by inducing aggregation in the absence of calcium. This effect on self-assembly is specific in that it is observed with heparin but not with several heparan sulfates or other glycosaminoglycans: it correlates with affinity and depends on the degree of polysaccharide sulfation. Heparin binds to laminin in a calcium-dependent manner with a single class of interaction (KD = 118 +/- 18 nM) and with a binding capacity of one heparin for two laminins. We find the long arm globule (E3) is the only laminin domain which exhibits substantial heparin binding: heparin binds E3 with an affinity (KD = 94 +/- 12 nM) and calcium dependence similar to that for intact laminin. These data strongly suggest that heparin modifies laminin assembly by binding to pairs of long arm globular domains. As a result the polymer may be stabilized at domain E3 and laminin interdomain interactions induced or modified. We further postulate that heparins may act in vivo as specific regulators of the structure and functions of basement membranes by both altering the laminin matrix and by displacing weakly binding heparan sulfates.

White-light joint-transform correlator

The spatial and temporal coherence requirements in the formation of the joint-transform hologram and in the readout process are described, and experimental results are given.