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PubMed1989

Ethics and animals.

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Animal Care Committees↗
PubMed1992

Degeneration of osteoblasts involved in intramembranous ossification of fetal rat calvaria.

Ossification of calvariae from day-21 rat fetuses was reinvestigated by electron microscopy using different fixation techniques (glutaraldehyde/OsO4, tannic acid, ruthenium red, K-pyroantimonate). An osteoid layer with scattered mineral deposits was found at the mineralization front. Directly beyond this layer, a sheet of one to two layers of necrotic and degenerating osteoblasts was present. Above this sheet, normal and healthy cells were seen, formed by six to eight layers of flattened cells, embedded in a collagenous matrix. The osteoblasts on the less mineralizing opposite side of the calcified calvariae and the osteocytes embedded in the calcified calvariae appeared healthy. Closer inspection of the necrotic zone revealed apatite crystals in vesicles which most probably originated from mitochondria of the degenerated cells. Large K-pyroantimonate deposits were found throughout the osteoid and the necrotic zone, whereas only small granules were scattered in the cytoplasm and at the plasma membrane of the healthy cells directly adjacent to the necrotic zone. A concept of intramembranous mineralization is outlined, according to which osteoblasts store enormous amounts of calcium, which are liberated by physiological cell death in the vicinity of the mineralizing front.

Animals↗
PubMed1997

Purification of the cardiac sarcoplasmic reticulum membrane protein phospholamban from recombinant Escherichia coli.

Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification.

Animals↗
PubMed2003

Dentin extracellular matrix (ECM) proteins: comparison to bone ECM and contribution to dynamics of dentinogenesis.

Dentinogenesis involves the initial odontoblastic synthesis of a collagen-rich extracellular matrix (ECM) and predentin that is converted to dentin when the collagen fibrils become mineralized. Since the width of predentin is rather uniform, we postulate that extracellular events regulate dentinogenesis. Similarly, osteogenesis involves an initial unmineralized osteoid that is mineralized and converted to bone. To gain insights into these two processes, we compared ECM proteins in bone with those in dentin, focusing upon the sialic acid (SA)-rich proteins. We observed qualitative similarities between the SA-rich proteins, but distinct differences in the amounts of osteopontin (OPN) and dentin sialoprotein (DSP). OPN, a predominant protein in bone, was found in much smaller amounts in dentin. Conversely, DSP was abundant in dentin ECM, but found sparingly in bone. Molecular cloning experiments indicate that coding sequences for DSP and dentin phosphoprotein (DPP) are found on the same mRNA. We believe that the initial form of the precursor protein DSPP is inactive in influencing the mineralization process and that it must be activated by cleavage of peptide bonds in conserved regions. Thus, unknown proteinases would act on DSPP, possibly at the mineralization front, and liberate active DPP, which plays an initiation and regulatory role in the formation of apatite crystals. This post-translational processing reaction would represent an important control point in dentinogenesis. Recently, we identified uncleaved DSPP in dentin extracts, which should allow us to test portions of our hypothesis.

Amino Acid Sequence↗
PubMedDate not supplied

Esters of cephalosporins. Part I. Permeability of cefuroxime liberated from its 1-acetoxyethyl ester through biological membranes; influence of the form and size of the ester particles.

Concentrations of cefuroxime [II] in blood of rats were measured 30 and 60 min. after administration of amorphous form possessing various particles size (ranging from 0.09 to 0.4 nm) and crystal form of 1-acethoxyethyl ester of cefuroxime [I]. In vitro the concentrations of [II] were measured 15 and 45 min. after application of [I]. HPLC method was used for cefuroxime estimation. Close correlation between the particles size of the amorphous [I] and the concentrations of [II] in vivo as well as in vitro was found, the particles with lover size possessed higher bioavailability. The cefuroxime front the crystal form of ester is poorly absorbed and the concentrations of [II] after its application were similar to those observed after of the bigest particles of amorphous form both in vivo and in vitro.

Animals↗
PubMedDate not supplied

Generation of beta-globin by sequence-specific proteolysis of a hybrid protein produced in Escherichia coli.

High-level expression of many eukaryotic genes has proved difficult to achieve even when a strong promoter and the ribosome binding sequence from highly expressed Escherichia coli genes have been placed in front of the coding sequences. To overcome this problem, many eukaryotic proteins have been efficiently produced as hybrids after fusion of their genes with a coding sequence of E. coli genes. However, such hybrid proteins are not suitable for functional studies or clinical use unless the authentic protein sequence can be released by specific cleavage. Here, we have inserted the sequence Ile-Glu-Gly-Arg between the 31 amino-terminal residues of lambda cII protein and Val 1 of human beta-globin, and produced this hybrid in high yield in E. coli. We then cleaved the hybrid specifically at the single arginine, using blood coagulation factor Xa and thus liberated the authentic beta-globin chain. As factor Xa is specific for the tetrapeptide Ile-Glu-Gly-Arg, which is rare in protein sequences, our expression/cleavage system is applicable to the efficient production of many eukaryotic proteins.

Amino Acid Sequence↗
PubMed2006

Pericellular proteases in angiogenesis and vasculogenesis.

Pericellular proteases play an important role in angiogenesis and vasculogenesis. They comprise (membrane-type) matrix metalloproteinases [(MT-)MMPs], serine proteases, cysteine cathepsins, and membrane-bound aminopeptidases. Specific inhibitors regulate them. Major roles in initiating angiogenesis have been attributed to MT1-matrix metalloproteinase (MMP), MMP-2, and MMP-9. Whereas MT-MMPs are membrane-bound by nature, MMP-2 and MMP-9 can localize to the membrane by binding to alphavbeta3-integrin and CD44, respectively. Proteases switch on neovascularization by activation, liberation, and modification of angiogenic growth factors and degradation of the endothelial and interstitial matrix. They also modify the properties of angiogenic growth factors and cytokines. Neovascularization requires cell migration, which depends on the assembly of protease-protein complexes at the migrating cell front. MT1-MMP and urokinase (u-PA) form multiprotein complexes in the lamellipodia and focal adhesions of migrating cells, facilitating proteolysis and sufficient support for endothelial cell migration and survival. Excessive proteolysis causes loss of endothelial cell-matrix interaction and impairs angiogenesis. MMP-9 and cathepsin L stimulate the recruitment and action of blood- or bone-marrow-derived accessory cells that enhance angiogenesis. Proteases also generate fragments of extracellular matrix and hemostasis factors that have anti-angiogenic properties. Understanding the complexity of protease activities in angiogenesis contributes to recognizing new targets for stimulation or inhibition of neovascularization in disease.

ADAM Proteins↗
PubMed1991

Study of mammalian selenocysteyl-tRNA synthesis with [75Se]HSe.

The mechanisms of the synthesis of mammalian selenocysteyl-(Scy)-tRNA were studied using [75SE]H2Se. H2Se was prepared from [75Se]selenite, glutathione, NADPH and glutathione reductase, and was purified by chromatography. It was confirmed that this H2Se was a Se donor in the reaction of the synthesis of Scy-tRNA. [75Se]Scy, liberated from aminoacyl-tRNA, was analyzed by TLC on silica gel an subsequent autoradiography. The activity of Scy-tRNA synthesis was found in the supernatant at 105,000 x g of the murine liver extract, but not in the precipitate. The supernatant was chromatographed on DEAE-cellulose, and the activity was eluted at a concentration of 0.17 M KCl. This position is at the front shoulder of the peak of seryl-tRNA synthetase which was eluted at 0.20 M KCl. Major serine tRNA(IGA) is not a substrate on which to synthesize Scy-tRNA, but natural opal suppressor serine tRNA is. On a chromatographic pattern of a Scy-tRNA preparation on Sephacryl S-200, the radioactivity of 75Se was eluted at the tRNA peak. This showed that Scy bound to tRNA. The active protein fraction from DEAE-cellulose did not contain tRNA kinase, therefore Scy-tRNA must be directly synthesized from seryl-tRNA, not through phosphoseryl-tRNA. This mechanism is similar to that seen in Escherichia coli [1991, J. Biol. Chem. 266, 6324].

Animals↗
PubMed1997

[Electrophysiologic studies of local ion transport changes in the tracheal wall in vitro].

It is generally accepted that stimulation of sensory receptors of airways provokes cough reflex and liberates neuropeptides which influence the smooth muscle tonus, mucosal blood flow and secretion of mucus. The study tests the hypothesis that mechanical stimulation of airway wall changes also epithelial ion transport and in this way influences physiological performance of the organ. The global evaluation of ion transport was accomplished by measurements of transepithelial electrical potential difference and resistance of the front part of a wall of isolated rabbit trachea which was mounted in an Ussing apparatus (Fig. 1, Tab. 1). In response to a gentle rinsing of tracheal mucosal surface by isoosmotic bathing fluid it reacted with transient increases of both potential difference and current (Fig. 2, Tab. 2). Gentle touching of the mucosal surface also elicited changes and a stepwise return to the baseline value of potential difference. Application of the stimuli from the antilumenal side usually but not invariably failed to produce any changes in potential difference or current. Measurements of mechanosensitive changes of electrical potential difference in secretory or reabsorptive states of tracheal wall (modelled by inhibition of sodium or chloride transepithelial transport) revealed that according to functional status of epithelium sodium or chloride ions transport changes are responsible for the reactions (Fig. 4). We put forward the hypothesis that mechanosensitive changes of ion transport of airways in vivo could be responsible for adequate changes in the status of respiratory tract epithelial fluid lining during the cough reflex (Fig. 5).

Amiloride↗