The interaction of prostaglandins with serum low-density lipoproteins

The interaction of human serum low-density lipoproteins (LDL) with various types of prostaglandins (PG) was studied using equilibrium dialysis, steady-state fluorescence polarization spectroscopy and photolabeling methods. Low concentrations (10(-13)-10(-9) M) of PGE1 and PGF2 alpha were shown to induce specific rearrangements of the lipids on the LDL surface, whereas the closely related PGE2 and PGF1 alpha had no effect. With fluorescent labeled LDL, the PGE1-induced changes of the steady-state fluorescence polarization (P) were shown to be time- and concentration-dependent, saturable and reversible. However, equilibrium dialysis revealed a very low binding capacity of LDL for PGE1 (approx. 1 prostaglandin molecule per 600 LDL particles). Approximately the same PGE1 concentration was sufficient to cause maximal changes of P, to enhance the binding to apolipoprotein B of a photoreactive sphingomyelin analogue inserted into the LDL surface and to alter the thermal phase behavior of the LDL surface lipids. It is proposed that the LDL surface rearrangement caused by prostaglandins is due to the interaction of prostaglandins with apolipoprotein B, resulting in formation of short-lived complexes. The mechanism of this interaction is discussed in terms of the non-equilibrium ligand-receptor interaction model proposed earlier to explain the interaction of prostaglandins with high-density lipoproteins (Bergelson, L.D. et al. (1987) Biochim. Biophys. Acta 921, 182-190). It is suggested that direct prostaglandin-lipoprotein interactions may play a role in the homeostasis of cholesterol.     

Alternative cyclization in GFP-like proteins family. The formation and structure of the chromophore of a purple chromoprotein from Anemonia sulcata

Anemonia sulcata purple protein (asFP595) belongs to a family of green fluorescent protein (GFP)-like proteins from the Anthozoa species. Similar to GFP, asFP595 apparently forms its chromophore by modifying amino acids within its polypeptide chain. Until now, the GFP-like proteins from Anthozoa were thought to contain chromophores with the same imidazolidinone core as GFP. Mass spectral analysis of a chromophore-containing tryptic pentapeptide from asFP595 demonstrates that chromophore formation in asFP595 is stoichiometrically the same as that in GFP: one H(2)O and two H(+) are released while a Schiff base and dehydrotyrosine are formed. However, structural studies of this asFP595 chromopeptide show that in contrast to GFP, the other peptide bond nitrogen and carbonyl carbon are required for chromophore cyclization, a reaction that yields the six-membered heterocycle 2-(4-hydroxybenzylidene)-6-hydroxy-2,5-dihydropyrazine. Spectrophotometric titration reveals three pH-dependent forms of the asFP595 chromopeptide: yellow (absorption maximum = 430 nm) at pH 3.0; red (absorption maximum = 535 nm) at pH 8.0; and colorless (absorption maximum = 380 nm) at pH 14.0. The pK(a) values for these spectral transitions (6.8 and 10.9) are consistent with the ionization of the phenolic group of dehydrotyrosine and deprotonation of the amidinium cation in the chromophore heterocycle, respectively. The amidinium group in asFP595 accounts for the unique absorption spectrum of the protein, which is substantially red-shifted relative to that of GFP. When the asFP595 chromophore cyclizes, the Cys-Met bond adjacent to the chromophore hydrolyzes, splitting the chromoprotein into 8- and 20-kDa fragments. High performance liquid chromatography analysis of a tryptic digest of denatured asFP595 shows that a pentapeptide with the cleaved Cys-Met bond is the only fragment associated with the red-shifted absorbance. These results imply that fragmentation of asFP595 is a critical step in protein maturation.     

Isolation and characterization of fragments of ATP-dependent protease Lon from Escherichia coli obtained by limited proteolysis

Conditions of limited proteolysis of the protease Lon from Escherichia coli that provided the formation of fragments approximately corresponding to the enzyme domains were found for studying the domain functioning. A method of isolation of the domains was developed, and their functional characteristics were compared. The isolated proteolytic domain (LonP fragment) of the enzyme was shown to exhibit both peptidase and proteolytic activities; however, it cleaved large protein substrates at a significantly lower rate than the full-size protease Lon. On the other hand, the LonAP fragment, containing both the ATPase and the proteolytic domains, retained almost all of the enzymatic properties of the full-size protein. Both LonP and LonAP predominantly form dimers unlike the native protease Lon functioning as a tetramer. These results suggest that the N-terminal domain of protease Lon plays a considerable role in the process of the enzyme oligomerization.     

Different influences of genomic imprinting on the development of parthenogenetic cell clones in C57BL/6 and CBA mice

Clonal analysis of parthenogenetic chimeric mouse embryos C57B1/6(PG)<-->BALB/c has shown that parthenogenetic cell clones C57BL/6 are present in the brain, liver, and kidneys of 14- and 18-day-old embryos. The content of the parthenogenetic component (PG) in these organs on day 18 was lower than on day 14, and, in some 18-day-old embryos, parthenogenetic cell clones were absent from the liver and/or kidneys. These data suggest that, during the embryogenesis of parthenogenetic chimeras, parthenogenetic cell clones of mostly endodermal and mesodermal origins were actively eliminated. Therefore, in such parthenogenetic adult chimeras, parthenogenetic clones of mostly ectodermal origins were preserved. In parthenogenetic chimeras CBA(PG)<-->BALB/c, parthenogenetic cell clones were actively eliminated at early embryonic stages, and, as a result, they were absent at the post-implantation stages. Hence, during development of parthenogenetic cell clones, the effects of genomic imprinting are expressed unequally in C57BL/6 and CBA mice.     

Proteins and saponins in the lipid preparation obtained by extraction of soybean flour

A complex lipid preparation was obtained by extraction of soybean flour with organic solvents. This preparation was shown to include not only phospholipids (major components), but also up to 30% saponins. These compounds were identified by TLC, HPLC, and 1H-NMR spectroscopy. Minor components of the lipid extract were represented by polypeptides associated with phospholipids via electrostatic or hydrophobic forces.     

Ploidy levels and the number of nuclei in cardiomyocytes of the lamprey and fish

It is well known that polyploidization of cardiomyocytes (CMC) is an essential component of heart growth in the warm-blooded vertebrates. Using the Feulgen cytophotometry of alkali-dissociated cells, we determined the ploidy in CMC of the lower vertebrates: lamprey Lampetra fluviatilis (Cyclostomata), skate Bathyraja maculata (Chondrostei), sterlet Acipenser ruthenus, and Russian sturgeon Acipenser güldenst?dti (Ganoids), as well as paradise fish Macropodus opercularis, Amur sleeper Perccottus glehni, and Atlantic salmon Salmo solar (Teleostei). The data obtained have demonstrated a wide variety in CMC ploidy of both cyclostomata and fishes. About 85% of the lamprey CMC contain 2 or more (up to 17) nuclei per cell; with 90 and 10% of the nuclei being, respectively, diploid and tetraploid. Hearts of the skate and sturgeons contain mononucleated diploid CMC. In the perch-like fishes, mononucleated diploid and mononucleated tetraploid CMC make, respectively, 95 and 5%. The salmon heart contains near 50% of mononucleated diploid CMC, 13% of mononucleated tetra- and octaploid CMC, the rest CMC being multinucleated (up to 6 nuclei per cell). In all the examined species, the increased nuclear ploidy is accompanied with a significant increase in the nuclear volume. The number of nucleoli per nucleus does not correlate with the nuclear ploidy level. Evolutionary aspects of CMC polyploidy in chordates are discussed.     

Undifferentiated cells in the snail myocardium are capable of DNA synthesis and myodifferentiation

Cellular mechanisms of heart-muscle growth in the snail Achatina fulica have been studied using cytophotometry and electron microscopic autoradiography. Cytophotometric DNA measurements showed that the snail cardiomyocytes are mononucleated cells with diploid nuclei. Ultrastructural analysis of the snail myocardium revealed that, in addition to mature myocytes, it contains small roundish undifferentiated cells (UCs) and poorly differentiated muscle cells. EM autoradiography detected silver grains over the nuclei of UCs 2 h after injection of tritiated thymidine ([(3)H]Tdr), while the nuclei of both mature and poorly differentiated myocytes remained unlabeled. In EM autographs of the myocardial tissue fixed 14 days after [(3)H]Tdr administration, labeled myonuclei were evident, which may suggest some myodifferentiation of prelabeled UCs. Many labeled UCs persist for 14 days after a single [(3)H]Tdr injection, suggesting that not all UCs undergo myodifferentiation after passing through the cell cycle, and that those that do not can enter the next cycle. UCs in the snail myocardium presumably provide not only reserve but also stem cells for myocytes. Thus, the heart muscle of the adult snail consists of mononucleated diploid myocytes with blocked proliferative activity and a renewable population of precursor myogenic cells. The results obtained suggest that the growth of this muscle involves a myoblastic mechanism of myogenesis; this mechanism differs from that of vertebrate cardiac muscle growth, which is non-myoblastic-that is, based on proliferation or polyploidization of cardiomyocytes. Evolutionary aspects of cellular mechanisms of the heart-muscle growth are discussed.     

Hsp70 in the atrial neuroendocrine units of the snail, Achatina fulica

Heat shock proteins (Hsps) are evolutionary conserved peptides well known as molecular chaperones and stress proteins. Elevated levels of extracellular Hsps in blood plasma have been observed during the stress responses and some diseases. Information on the cellular sources of extracellular Hsps and mechanisms regulating their release is still scanty. Here we showed the presence and localization of Hsp70 in the neuroendocrine system in the atrium of the snail, Achatina fulica. The occurrence of the peptide in snail atrium lysate was detected by Western blot analysis. Immunoperoxidase and immunogold staining demonstrated that Hsp70-immunoreactivity is mainly confined to the peculiar atrial neuroendocrine units which are formed by nerve fibers tightly contacted with large granular cells. Immunolabelling intensity differed in morphologically distinct types of secretory granules in the granular cells. The pictures of exocytosis of Hsp70-immunolabeled granules from the granular cells were observed. In nerve bundles, axon profiles with Hsp70-immunoreactive and those with non-immunoreactive neurosecretory granules were found. In addition, Hsp70-like material was also revealed in the granules of glia-interstitial cells that accompanied nerve fibers. Our findings provide an immuno-morphological basis for a role of Hsp70 in the functioning of the neuroendocrine system in the snail heart, and show that the atrial granular cells are a probable source of extracellular Hsp70 in the snail hemolymph.