Extraction and characterisation of the intact form of bovine vitreous type IX collagen

We provide the first biochemical characterisation of intact type IX collagen extracted from bovine vitreous. It possesses a shortened alpha 1(IX) chain (M(r) 64K) compared to its cartilage counterpart (M(r) 84K). All the vitreous type IX collagen is in a proteoglycan form, its glycosaminoglycan constituent being a chondroitin/dermatan sulphate component of M(r) 15-60K attached to the alpha 2(IX) chain. This contrasts with previous findings in chick vitreous where a very long glycosaminoglycan chain of M(r) approximately 350K was demonstrated.

The presence of phospholipase A2 in bovine adrenal medulla: arguments for more than one type of phospholipase A2

Since phospholipase A2 (PLA2) is expected to play a role in the mechanism of exocytosis, the presence and subcellular localization of PLA2 in bovine adrenal medulla have been studied. The results of this study reveal that, although a large part of the PLA2 activity in chromaffin cells is due to a lysosomal PLA2, a cytoplasmic PLA2 is also present. This finding is supported by experiments in which the influence of pH, CaCl2 and NaCl on cytoplasmic PLA2 as well as the binding capacity to concanavalin A are investigated. According to these results the properties of a cytoplasmic PLA2 are clearly different from those reported by other authors for the lysosomal PLA2. For this reason, in chromaffin cells a PLA2 could be present which remains in the cytosol when the cell is in rest. Future experiments will have to prove whether this PLA2 becomes associated with the plasma membrane upon stimulation of the cell, thus mediating exocytosis.

Topographical analysis of the G virion of Aleutian mink disease parvovirus with monoclonal antibodies

The topography of the Aleutian mink disease parvovirus (ADV) G virion was analyzed with monoclonal antibodies and polyclonal antiserum. There was homology between the two major structural proteins as others have previously reported. Trypsin treatment of the virion with subsequent immunoblotting revealed that VP2 represents the main peptide on the exterior of virion and that VP1 is probably embedded within the capsid. Additional analyses of the trypsin-treated virions showed that VP2 is responsible for binding complement and that it also represents the structural part of the virion that binds to cellular receptors. A third protein, p34, was detected that might represent a third structural polypeptide because of its many unique epitopes relative to the other peptides detected.

Effects of subcultivation and culture medium on differentiation of human fetal cardiac myocytes

Previous work has suggested that subcultivated human fetal heart muscle cell cultures contain immature cardiac muscle cells capable only of limited differentiation after mitogen withdrawal. We studied several human fetal heart cultures (14-15 wk gestation) at several passage levels using immunocytochemistry, autoradiography, and Northern blot analysis. Characteristics in high-mitogen (growth) medium were compared with those after serum withdrawal. Cultured cells from one heart, expanded through 2 passages in growth medium, did not beat; however, 75% of cells did beat after subsequent culture for 24 days in low-serum (differentiation) medium containing insulin. In confluent cultures after 1 passage, there was no detectable difference in the number of cardiac myocytes present in growth medium compared with that 7 days after serum withdrawal. After 4 passages, however, serum withdrawal increased the number of cells expressing immunoreactive sarcomeric myosin heavy chain by 100-fold; expression of immunoreactive sarcomeric actin and alpha-cardiac actin mRNA also increased in the same cultures. Similar results were obtained in cultures kept in differentiation medium for 20 days before passage and expansion in growth medium. Using isopycnic centrifugation, a high-density cell fraction was isolated which contained no immunostained myocytes in growth medium but numerous myocytes after serum withdrawal. Combined immunocytochemistry/autoradiography showed that myocytes synthesize DNA in growth medium and in serum-free medium containing fibroblast growth factor, but not in serum-free medium alone. The results indicate that a) human fetal cardiac muscle cells proliferate in vitro and can maintain a phenotype characteristic of fetal myocytes after multiple subcultivations followed by serum withdrawal; b) after subcultivation in growth medium, some myocytes modulate their phenotype into one in which detectable levels of cardiac contractile proteins are expressed only after mitogen withdrawal, and c) the phenotype attained after serum withdrawal is in part dependent on passage level. Cultured human fetal myocardial cells may provide a useful experimental system for the study of human cardiac muscle cell biology.

Ageing-related changes in Mycoplasma canadense membranes

Fluidity and composition of cell membranes during progression of Mycoplasma canadense cultures grown in a serum-free medium was assessed. The fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene at 25 degrees C of intact cells and liposomes in the exponential and stationary phases of growth was compared. A decrease in fluidity and an increase in the ratio of saturated to unsaturated fatty acids was detected in cell membranes on aging. Nevertheless, membrane density remained unaltered although the molar ratio of cholesterol to phospholipids decreased. It is proposed that the increase in lipid order is primarily due to the increase in the ratio of saturated to unsaturated membrane fatty acids, being the diminished molar ratio of cholesterol to phospholipids involved in the reduced unsaturated fatty acid uptake.

The isopycnic, compartmentalized integration of Rous sarcoma virus sequences

Rous sarcoma virus (RSV) can cause tumors in hamsters, which harbor complete or partially deleted RSV sequences, in their genomes. Here we have studied the localization of RSV sequences integrated into the genome of cell lines derived from six independent hamster tumors. We have found that integration occurred in the isochores richest in guanine + cytosine, of the host genome, as it had been previously observed for bovine leukemia and hepatitis B viral sequences. The integration of RSV proviral sequences is, therefore, 'isopycnic' (i.e., it takes place in host genome sequences which compositionally match the viral sequences) and compartmentalized (i.e., it occurs in a small compositional compartment of the host genome). The hamster genome compartment hosting RSV sequences precisely corresponds to a compartment of the human genome which is the most active in both transcription and recombination. The notion of a compartmentalized, isopycnic integration of RSV proviral sequences fits, therefore, with the viral integration into transcriptionally active and recombinogenic regions of the host genome observed by other authors, but is broader, in that it includes, in addition, the requirement for a compositional match between host genome sequences and expressed viral sequences.

Hydrogenosomal succinate thiokinase in Tritrichomonas foetus and Trichomonas vaginalis

Succinate thiokinase displays a diversity of nucleotide specificity and molecular size throughout Nature. Eukaryotes and Gram-positive bacteria possess distinct 'small' (dimeric) thiokinase enzymes which are specific for adenine (ADP) or guanine (GDP) nucleotides, whereas Gram-negative bacteria contain a single 'large' (tetrameric) enzyme which utilizes both nucleotides. Succinate thiokinase activities, both ADP- and GDP-dependent, were shown to be hydrogenosomal in Tritrichomonas foetus and Trichomonas vaginalis. Surprisingly, the 'small' enzyme was found in T. foetus whereas T. vaginalis contained a 'large' enzyme.

Identification and characterization of incomplete hepatitis A virus particles

The range of hepatitis A virus (HAV) particles generated during persistent infection of different cell lines was studied. Buoyant density and sedimentation analyses of cell extracts revealed a uniform profile of particles in all cell lines analysed except for BS-C-1 cells. The virion itself usually represented less than 50% of the total mass of virus antigen. A major portion of the antigen was associated with non-infectious, empty particles, which banded at 1.305 g/ml and 1.20 g/ml CsCl, and sedimented in sucrose gradients at 76S and 59S. Empty HAV particles were similar to those of poliovirus with respect to their physical stability and had the characteristic capsid protein content (VP0, VP1 and VP3). An additional RNA-containing particle, probably the provirion, represented only a minor species characterized by a buoyant density of 1.32 g/ml in CsCl and sedimenting at 130S.

Isolation, identification, and partial cDNA cloning of genomic RNA of jaagsiekte retrovirus, the etiological agent of sheep pulmonary adenomatosis

The genome of the jaagsiekte (JS) retrovirus (JSRV), the etiological agent of sheep pulmonary adenomatosis (jaagsiekte), has been identified, isolated, and partly cloned. The JSRV genome is ca. 8.7 kb long. cDNA of the genomic RNA was synthesized and cloned. A clone, JS 46.1, was isolated and characterized. It has an insert of 2.1 kb which hybridizes to the same 8.7-kb RNA in all the JSRV-infected sheep lung washes tested but does not hybridize to maedi-visna virus, a sheep lentivirus often found coinfecting JSRV-infected lungs. Comparison of the amino acid sequence encoded by JS 46.1 with those encoded by other retroviruses revealed that JSRV has homology to the type D and B oncoviruses and to human endogenous retrovirus.

RNA processing enzymes RNase III, E and P in Escherichia coli are not ribosomal enzymes

We recently showed that RNase III can process a small stable RNA, precursor 10Sa RNA, that accumulates in an rne (RNase E) strain at non-permissive temperatures. Precursor 10Sa (p10Sa) RNA is processed to 10Sa RNA in two steps, the first step is catalyzed by RNase III in the presence of Mn2+ but not Mg2+. It was shown that RNase III cosediments with membrane preparation from wild type as well as RNase III overexpressing cells. However, the possibility of membrane preparation contamination with ribosomes could not be ruled out. Here we show that RNase III, E and P are not associated with ribosomes. E. coli cells were opened either by alumina grinding or by sonication and fractionated into cytosolic and pellet fractions. The characterization of membrane preparations was done by assaying NADH oxidase, a bona fide membrane enzyme. Ribosomes prepared by alumina grinding were found to be contaminated with small fragments of membrane which contained RNase III activity. RNase III and NADH oxidase activities were present in the ribosomal preparations which could be solubilized by reagents that dissolve the inner membrane. Isopycnic sucrose gradient centrifugation of the membrane and ribosomal preparations also confirmed that RNase III fractionated with the inner membrane. Similarly RNase P activity was found in the corresponding fractions when isopycnic centrifugation of membrane and ribosome preparations was carried out. RNase E activity was also found to be present mostly in the post-ribosomal supernatant. These findings show that RNase III, E and P are not ribosomal enzymes.

Unexpected destruction of chitosomal chitin synthetase by an endogenous protease during sucrose density gradient purification

Because of their intrinsic low buoyant density, chitosomes can be separated from crude cell homogenates (1000 g or 35,000 g supernatants) of Mucor rouxii by isopycnic sedimentation in sucrose density gradients. To accelerate and simplify the isolation of chitosomes, we centrifuged the cell-free extracts at ultrahigh speed (in a fixed-angle rotor at forces up to 311,000 g Rav) and found that the duration of centrifugation was critical. Prolonged centrifugation at ultrahigh speed caused severe distortion of the chitin synthetase profile in the gradient as the peak of chitosomal chitin synthetase nearly disappeared. We traced the problem to a soluble protease(s) that moved into the chitosome band during protracted centrifugation and destroyed the chitin synthetase activity. The interfering protease was a soluble protein with a sedimentation coefficient of 4.6 S and a pH optimum of 7–7.5, and it was sensitive to PMSF (phenylmethylsulfonyl fluoride), indicating that it was a serine protease. Unlike other proteases, it destroyed chitin synthetase but did not activate the chitin synthetase zymogen. The interfering protease could be eliminated either by adding PMSF to the cells immediately after breakage or by removing the upper part of the sucrose gradient midway through the centrifugation of the cell-free extract and then completing the sedimentation with the ‘decapitated’ gradient.

Isolation of HnRNP particles from Drosophila melanogaster embryos

HnRNP from nitrogen frozen Drosophila melanogaster embryos were isolated in the presence of EDTA and EGTA cosedimenting in sucrose and density gradients like hnRNP from vertebrates. Four "core" proteins of 23.000, 28.000, 32.000 and 45.000 Da are strongly enriched in these complexes. One could conclude that the basic structural organization of Drosophila melanogaster hnRNP is similar to that described for vertebrates.

Transient membrane association of the precursors of cathepsin C during their transfer into lysosomes

Transport of the lysosomal enzyme cathepsin C was studied in Morris hepatoma 7777 cells. Subcellular fractions obtained after isopyenic centrifugation in sucrose gradients of labelled cell homogenates were sequentially extracted by hypo-osmotic shock, Na2CO3 and Triton X-100. Polypeptides related to cathepsin C were immunoprecipitated and analysed by SDS/PAGE and fluorography. At early times after synthesis and for up to 60 min, precursor polypeptides of cathepsin C are distributed in endoplasmic reticulum and Golgi fractions, in membrane-associated form, as Triton X-100 is necessary for their extraction. At 2 h and later after synthesis, intermediate and mature forms of the enzyme can be totally extracted by hypo-osmotic shock from gradient fractions corresponding to the lysosomes of Morris hepatoma 7777 cells.

Mucins in cat airway secretions

Mucous secretions were obtained from cat tracheas that had received [3H]glucose and [35S]sulphate to radiolabel mucus glycoproteins biosynthetically. Samples were collected under resting ('basal') conditions as well as after pilocarpine stimulation and were separated into gel and sol phases by centrifugation. Macromolecules were partially purified by using gel chromatography on Sepharose CL-4B, and the species that were eluted with the void volume were then separated into two major populations with isopycnic density-gradient centrifugation in CsCl. The major component from the gel phase of pilocarpine-induced secretions had a buoyant density typical of mucins and was observed as linear and apparently flexible chains by electron microscopy. Reduction of disulphide bonds gave subunits that could be further cleaved by trypsin digestion into components of approximately the same size as the high-Mr glycopeptides obtained from other mucins after this treatment. In contrast, the dominant species in the gel phase of the 'basal' secretion had a significantly higher buoyant density than expected for mucins and was largely unaffected by reduction, as studied by gel chromatography. The macromolecules were fragmented by trypsin, suggesting that they contain a polypeptide backbone. This more dense component also predominated in the sol phase both from the 'basal' secretions and from the pilocarpine-released secretions. Digestion with DNAase, chondroitin ABC lyase or heparan sulphate lyase had no effect, which shows that this component is not DNA, a dermatan sulphate/chondroitin sulphate or a heparan sulphate proteoglycan. In contrast, endo-beta-galactosidase and keratanase caused some fragmentation, suggesting that the molecules contain some linkages of the poly-(N-acetyl-lactosamine) type, although the degradation was not as extensive as expected for keratan sulphate. Treatment with alkaline borohydride resulted in extensive fragmentation of the high-Mr glycopeptides from both components, indicating that the glycans were oligosaccharides that were probably O-linked. The monosaccharide compositions of both components were consistent with that expected for mucins. The data are in keeping with the major component from the pilocarpine-stimulated gel secretions being a mucus glycoprotein and the more dense component being a mucin-like molecule, possibly related to the keratanase-sensitive material isolated from canine trachea by Varsano, Basbaum, Forsberg, Borson, Caughey & Nadel [(1987) Exp. Lung Res. 13, 157-184].

Peplomycin-induced DNA repair synthesis in permeable mouse ascites sarcoma cells

DNA repair synthesis induced in permeable mouse ascites sarcoma cells by peplomycin, an antitumor antibiotic, was studied. Mouse ascites sarcoma (SR-C3H/He) cells were permeabilized with a low concentration of Triton X-100 in an isotonic condition. Permeable cells were treated with an appropriate concentration of peplomycin to introduce single-strand breaks in permeable cell DNA. DNA repair synthesis in peplomycin-treated permeable cells was measured by incubating the cells with four deoxynucleoside triphosphates in an appropriate buffer system. The DNA repair synthesis was enhanced by ATP and NaCl at near physiological concentrations. More than 90% of DNA synthesis in the present system depended on the peplomycin-treatment. The repair nature of the DNA synthesis was confirmed by a BrdUMP density shift technique. The repair patches were largely completed and ligated in the presence of ATP. Analyses using selective inhibitors for DNA polymerases showed that both DNA polymerase Beta and aphidicolin-sensitive DNA polymerases (DNA polymerase alpha and/or delta) were involved in the repair DNA synthesis.

Biological and physicochemical characterization of the major (1.40) and minor (1.45) component of infectious avian adeno-associated virus

Two infectious components with buoyant densities of 1.40 g/cm3 and 1.45 g/cm3, designated as major (1.40) and minor (1.45) component, were detected by banding avian adeno-associated virus (AAAV) isopycnically in CsCl. In metrizamide, however, infectious AAAV banded only as a single peak at a density of 1.32 g/cm3. Biological as well as physicochemical properties of the two AAAV components recovered from CsCl density gradient were described. Concerning the minor (1.45) component, three experimental findings may suggest that the capsid structure of this AAAV population is altered in comparison with that of the major (1.40) component: (i) the sedimentation pattern characterized by an additional peak containing slower-sedimenting noninfectious material (16 S); (ii) the specific infectivity decreased by the 3.5 fold; (iii) the ready disintegration when exposed to gently denaturing conditions.

Domains of yeast plasma membrane and ATPase-associated glycoprotein

In yeast homogenates the plasma membrane H(+)-ATPase and a major surface glycoprotein of about 115 kDa are present in two membrane fractions with peak densities in sucrose gradients of 1.17 and 1.22. Immunogold electron microscopy of frozen yeast sections indicates that the ATPase is exclusively (greater than 95%) present at the surface membrane. Therefore the two ATPase-containing fractions appear to correspond to different domains of the plasma membrane. The 115 kDa glycoprotein is tightly associated with the ATPase during solubilization and purification of the enzyme. However, in a mutant lacking the glycoprotein the activity of the plasma membrane H(+)-ATPase is similar to wild type, suggesting that this association is fortuitous. The ATPase and the glycoprotein are difficult to separate by electrophoresis and therefore binding of concanavalin A to the ATPase cannot be unambiguously demonstrated in wild-type yeast. By utilizing the mutant without glycoprotein it was shown that the ATPase band of 105 kDa binds concanavalin A.

Proteoglycans nondissociatively extracted from different zones of canine normal articular cartilage: variations in the sedimentation profile of aggregates with degree of physiological stress

Proteoglycans were extracted and purified without dissociation (a-A1 preparations) from superficial and deeper layers of high weight-bearing (HWA) and low weight-bearing (LWA) areas of dog normal articular cartilage. These proteoglycans were then characterized by velocity gradient centrifugation. In each of the 4 different topographical regions, the weight average sedimentation coefficients related strongly with total hexuronate content of the tissue. In the superficial layers, almost all aggregates had low sedimentation coefficients: the aggregates were smaller and less abundant in LWA than in HWA. The deeper layers contained an additional population of faster sedimenting aggregates which appeared smaller and less abundant in LWA than in HWA. Quantification and functional characterization of aggregates as well as in vitro aggregating studies showed that the topographical differences in size and content of aggregates were related to differences in content of hyaluronate and link protein in the a-A1 preparations. Superficial a-A1 specimens contained twice as much hyaluronate as deeper a-A1 preparations and their hyaluronate content increased with degree of physiological stress. Deeper a-A1 specimens from weight-bearing areas did not differ in their hyaluronate content but experiments assessing the saturation with link protein of these different a-A1 preparations suggested that specimens from HWA contained more active link than those from LWA. In contrast, the capacity of aggregation of a-A1D1D1 proteoglycan monomers as well as the molecular weight (Mr = 5 x 10(5) and aggregating capacity of hyluronate molecules appeared very similar in all a-A1 preparations from areas of articular cartilage. It is hypothesized that the synthesis of the three constituents necessary for aggregate formation (i.e. proteoglycan monomers as well as hyaluronate and link protein molecules) increases with degree of physiological load and that aggregation helps to maintain within cartilage the high concentration of proteoglycans that are essential for its biomechanical functions. The reported topographical variations in the distribution of proteoglycan aggregates reflect probably a maximal adaptation of the physiologic and biomechanical properties of the matrix to meet the high stress levels experienced by the articular cartilage in vivo.

Biochemical characterisation of mitochondrial and lysosomal particles in foetal and neonatal rats

1. The sedimentation coefficients of the mitochondria are larger in the foetal as compared to the adult rats. For cytochrome oxidase, the values are respectively 18.700 x 10(3) and 13,550 x 10(3) S. 2. Lysosomal sedimentation coefficients are smaller in the foetal as compared to the adults. For beta galactosidase, the values are respectively 5.090 x 10(3) and 10.430 x 10(3) S. 3. It is concluded that the mitochondria are larger and the lysosomes smaller in size in the foetus as compared to the adults. 4. The external membrane of neonatal mitochondria and the membrane of foetal and neonatal lysosomes are more resistant to osmotic swelling.

Partial characterization of a turkey enterovirus-like virus

Small round viruses, 18 to 24 nm in diameter, were detected by electron microscopy in droppings of young turkeys with enteritis. The virus was propagated in embryonated turkey eggs and tentatively identified as an enterovirus based on size, intracytoplasmic morphogenesis, buoyant density of 1.33 g/ml in CsCl, and a single-stranded RNA genome of approximately 7.5 kb. It was distinguished from avian encephalomyelitis virus by cross-immunofluorescence. These results identify an enterovirus-like virus as a possible etiologic agent of enteric disease of young turkeys. However, its role in this disease remains to be established.

DNA modification in vivo by derivatives of glucose: enhancement by glutathione depletion

When BHK or HTC cells are cultured for 20 min with [U-14C]glucose in the presence of agents that deplete reduced glutathione, DNA banded from the cells in cesium salt gradients containing guanidium HCl is radioactively labeled. This depletion-dependent labeling required live cells. It was not caused by reactive contaminants in the radioactive glucose preparations, by carbohydrate or protein comigration into the DNA band, or by metabolism of glucose into deoxyribose. Labeling levels are similar whether depletion is achieved by oxidation (with the drug diamide) or by inhibition of synthesis (with methionine sulfoximine). A temporal association between GSH repletion and the appearance of D-lactate, the putative unique product of GSH-dependent glyoxylase action on pyruvaldehyde, suggests possible involvement of 3-carbon dicarbonyls.

Calmodulin-binding proteins in granule and plasma membranes from bovine chromaffin cells

Calmodulin-binding proteins in chromaffin granule membrane and chromaffin cell plasma membranes have been investigated and compared. Chromaffin granules were purified by centrifugation over a 1.7 M sucrose layer. Plasma membranes were obtained in a highly purified form by differential and isopycnic centrifugation. Enzymatic determinations of 5'-nucleotidase, a generally accepted plasma membrane marker, showed a 40-50-fold enrichment as compared to the cell homogenate. Marker enzyme studies demonstrated only minimal contamination by other subcellular organelles. After solubilization with Triton X-100, calmodulin-binding proteins were isolated from chromaffin granule membranes and plasma membranes by affinity chromatography on a calmodulin/Sepharose 4B column. On two-dimensional polyacrylamide gelelectrophoresis a prominent protein (Mr = 65,000, pI ranging from 5.1 to 6) consisting of multiple spots, was present in the calmodulin-binding fraction from chromaffin granule membranes as well as from plasma membranes. Besides this 65 kDa protein both fractions had at least four groups of proteins in common. Also, proteins typical for either preparation were observed. In the calmodulin-binding protein preparations from chromaffin granule membranes a prominent spot with Mr = 80,000 and a pH ranging from 5.0 to 5.7 was present. This protein was enzymatically and immunologically identified as dopamine-beta-monooxygenase.

Analytic subcellular fractionation of acini from rat lacrimal gland

A recent hypothesis for the cellular mechanism of fluid secretion by lacrimal acini has been based, in part, on the results of subcellular fractionation analyses of lacrimal gland fragments which had been incubated for a brief period in vitro. An important assumption in those studies was that the ion transporters and neurotransmitter receptors measured in isolated subcellular fractions were associated with membranes derived from the acinar cells, since these comprise the bulk of the lacrimal gland mass. This study was undertaken to validate this assumption. Acinar complexes were isolated from rat exorbital lacrimal glands by digestion with collagenase, hyaluronidase, and DNase. Although terminal intralobular duct segments and myoepithelial cells were occasionally noted, the preparations appeared to be free of larger ducts, blood cells, blood vessels, and interstitial cells. Acinar cells were then disrupted, and the homogenates underwent the fractionation procedure used previously for lacrimal gland fragment preparations. This procedure involved a sequence of analyses by differential sedimentation, isopycnic centrifugation on sorbitol gradients, and partitioning in dextran-polyethyleneglycol two-phase systems. Calculated initial specific activities for sodium/potassium adenosinetriphosphatase (Na+/K(+)-ATPase), alkaline phosphatase, acid phosphatase, and succinate dehydrogenase were identical to those obtained from fragment preparations. Major membrane populations resolved by the sequential analyses, including one believed to represent endoplasmic reticulum membranes, two believed to be derived from the acinar cell basal-lateral membrane, and two believed to be derived from the Golgi complex, corresponded closely to populations resolved from lacrimal fragment preparations. In addition to validating the previous use of lacrimal gland fragment preparations in studies of acinar cell function, these results suggest that preparations of isolated lacrimal acini will be useful for future work on neurotransmitter-receptor regulation and basal-lateral plasma membrane dynamics in the lacrimal gland.